The following description is from Flora of China Editorial Committee (2016)
M. jalapa is reported as being a weed in apple orchards (CONABIO, 2016). Its allelopathic effects can inhibit the germination and growth of wheat and cabbage (Xu et al., 2008).
Cells of E. amylovora are Gram negative rods, 0.3 x 1-3 µm in size, occur singly, in pairs and sometimes in short chains, and are motile by two to seven peritrichous flagella per cell (see Paulin, 2000, for review).
E. amylovora forms colonies of characteristic colour and colony formation on most culture media (Bereswill et al., 1998). Colonies are domed, circular, mucoid on sucrose nutrient agar (Billing et al., 1961);red to orange on MS medium (Miller and Schroth, 1972);white, circular, mucoid on KB medium (Paulin and Samson, 1973);smooth large, pulvinate, light blue opalescent with craters on CCT medium (Ishimaru and Klos, 1984);and yellow, highly mucoid or less mucoid on MM2Cu media (Bereswill et al., 1998).
Water-soaked flowers, spurs, or shoot tips accompanied by ooze production, followed quickly by necrosis, are early symptoms of fire blight. These symptoms can be detected in an orchard or nursery by experienced observers, but may be overlooked by the inexperienced.
A suitable period for inspection is 3-5 weeks after the blossom period. Look for necrotic leaves and branches, withered blossoms, crooked shoot tips, and ooze. Ooze is more likely to be present in the morning when air humidity is high and host water potential is positive;later in the day when the air is dry, ooze may be shiny and glassy.
Cankers may form on branches and trunks at the junction between infected and healthy bark tissues;therefore, inspections may be needed every 5-7 days throughout the summer or until no new infections are observed.
In autumn, mummified fruits and leaves hanging on dead branches is an indication of fire blight. In winter, the debris helps in locating cankers since the darker bark associated with old infection can blend in with the dormant healthy bark, particularly on older trees.
Fire blight's basic symptom is necrosis or death of tissues. Droplets of ooze on infected tissues are also an important symptom;they are the visible indication of the presence of fire blight bacteria. Except for minor differences, the symptoms of fire blight are basically the same on all host plants.
Infected blossoms initially become water-soaked and of a darker green as the bacteria invade new tissues. Within 5-30 plus days (commonly 5-10 days), the spurs begin to collapse, turning brown to black. Initial symptoms are often coincident with the accumulation of about 57 degree days, base 12.7°C, from the infection date (Steiner, 2000).
Infected shoots turn brown to black from the tip;shoots often bend near the tip to form a so-called 'shepherd-crook' shape. Shoots invaded from their base exhibit necrosis of basal leaves and the stem. Leaves and fruits may be invaded through petioles or stems or infected through wounds, resulting in discoloration followed by collapse of the leaves and fruit. During wet, humid weather, infected leaves and particularly the fruit often exude a milky, sticky liquid, or ooze containing bacteria.
From infected flowers and shoots, the bacteria may invade progressively larger branches, the trunk and even the rootstock. Infected bark on branches, scaffold limbs, trunk and rootstock turns darker than normal. When the outer bark is peeled away, the inner tissues are water-soaked often with reddish streaks when first invaded;later the tissues are dark brown to black. As disease progression slows, lesions become sunken and sometimes cracked at the margins, forming a canker.
Trees with rootstock blight may exhibit liquid bleeding from the crown at or just below the graft union in early summer. Water-soaked, reddish and necrotic tissues are visible when the outer bark is removed. Trees with infected rootstocks often exhibit yellow to red foliage about a month before normal autumn coloration. Rootstocks such as M.26, M.9 and relatives of M.9 often show these symptoms without evidence of infection in the trunk of the scion. Infection of M.7 and a few other rootstocks occurs following infection of suckers arising from the rootstocks;the infected suckers exhibit typical shoot blight symptoms. Many trees with rootstock blight will die in the first year after infection;the remaining rootstock-infected trees often die within 2-3 years.
Any plant tissues invaded by the bacteria can show ooze production on their surface. This exudate is a specific symptom of fire blight. Depending on weather conditions and on the time of the day, ooze may or may not be produced. It is most frequently observed early in the morning when the host water potential is positive. It may appear in different ways: droplets, threads or film on the plant's surface.
The long distance spread of fire blight is a rare event which in most cases seems to be the result of plants or plant tissues being moved across the oceans. Short distance spread is the result of the characteristics of the pathogen, especially its ability to produce an exudate (bacteria embedded in exopolysaccharides) which is easily transported by wind, rain, insects or birds. This is very efficient;once the pathogen has moved into a new territory it almost always colonizes and becomes established. This is accompanied by economic losses in regions where apple, pear or loquat are grown commercially;it might prevent the survival of local cultivars and could disrupt international trade. To date fire blight has colonized most of North America, Western Europe and most of the countries around the Mediterranean Sea as well as New Zealand. Outbreaks of fire blight are irregular and difficult to control.
E. amylovora is a pathogen of plants in the family Rosaceae;most of the natural hosts are in the subfamily Maloideae (formerly Pomoideae), a few belong in the subfamilies Rosoideae and Amygdaloideae (Momol and Aldwinckle, 2000). Genera in the subfamily Spiraeoideae have been reported as hosts on the basis of artificial inoculation (van der Zwet and Keil, 1979).
Strains of E. amylovora isolated from one host are pathogenic on most other hosts. This was the case for strains isolated from natural infections on Prunus salicina in the USA (Mohan and Thomson, 1996) and on Prunus domestica and Rosa rugosa in southern Germany (Vanneste et al., 2002a). Rubus strains (see Taxonomy and Nomenclature) are host specific;they are pathogenic on brambles but not on apple and pear (Starr et al., 1951;Braun and Hildebrand, 2005). Also, a few Maloideae strains exhibit differential virulence on apple;for example, strain Ea273 was not pathogenic across the same range of apple cultivars and rootstocks as common strain E4001A (Norelli et al., 1984, 1986).
Within each group of susceptible host plants, species or cultivars may be found with a high level of resistance;such plants may show no, or limited, symptoms under natural conditions or even following artificial inoculation (Forsline and Aldwinckle, 2002;Luby et al., 2002). Lists of resistant cultivars are published for important crops (van der Zwet and Keil, 1979;Zeller, 1989;Thomas and Jones, 1992;Berger and Zeller, 1994;van der Zwet and Bell, 1995;Bellenot-Kapusta et al., 2002).
Wild Pyrus (P. amygdaliformis, P. syriaca) in southern Europe and in the Mediterranean area, Crataegus (C. oxyacantha [ C. laevigata ], C. monogyna) in northern and central Europe, and ornamentals (Pyracantha, Cotoneaster, Sorbus) throughout Europe are important sources of inoculum for apple and pear orchards.
X. fastidiosa is a fastidious Gram-negative, xylem-limited bacterium, rod-shaped with rippled cell walls. It is strictly aerobic (microaerophilic), non-flagellate, does not form spores and measures 0.1-0.5 x 1-5 µm. The peach strain was given by Nyland et al. (1973) as 0.35 x 2.3 µm. See also Bradbury (1991). Thread-like strands (fimbriae) attached to the polar ends of bacterial cells can be observed in electron microscopy (Mircetich et al., 1976) and scanning electron microscopy (Feil et al., 2003b). These probably function in bacterial attachment and 'twitching' movement (Meng et al., 2005).
Symptoms are not reliable for detection of infected plants in transit.
X. fastidiosa can be detected microscopically (light or electron) in vessels in cross-sections of petioles (French et al., 1977) or by examining xylem sap squeezed from symptomatic stems or petioles or flushed from stems or petioles onto microscope slides (De Lima et al., 1998). Flushing of xylem sap from shoots with a pressure chamber allows the testing of larger sample sizes and avoids inhibitors for PCR (Bextine and Miller, 2004). Methods such as grafting to susceptible indicator plants or vector tests (Hutchins et al., 1953) are still available, and may have their place in certification schemes in which woody indicators are routinely used. X. fastidiosa can also be isolated onto suitable selective media (Davis et al., 1978, 1983;Raju et al., 1982;Wells et al., 1983). The identity of cultured bacteria can be confirmed by SDS-PAGE (Bazzi et al., 1994). Serological methods are less sensitive (10- to 100-fold) than culture but are the easiest means of detecting and identifying the bacterium, by ELISA or use of fluorescent antibodies (French et al., 1978;Walter, 1987;Hopkins and Adlerz, 1988;Sherald and Lei, 1991). Strains differ in quantitative reaction to antisera and in ease and efficiency of culture. DNA hybridization probes and PCR primers specific to X. fastidiosa have been developed (Firrao and Bazzi, 1994;Minsavage et al., 1994). X. fastidiosa can also be detected in its insect vectors (Yonce and Chang, 1987). The characterization and identification of strains chiefly employs molecular genetic methods (e.g., Chen et al., 1992;Hendson et al., 2001;Coletta-Filho et al., 2003), and can be expected to remain indefinitely in a state of change.
Different diagnostic methods used or developed for the detection and identification of X. fastidiosa are detailed in Janse (2009). Recent advances in detection include on-site molecular detection using real-time loop-mediated isothermal amplification (Yaseen et al., 2015).
The most characteristic symptom of primary infection is leaf scorch. An early sign is sudden drying of part of a green leaf, which then turns brown while adjacent tissues turn yellow or red. The desiccation spreads and the whole leaf may shrivel and drop, leaving only the petiole attached. Diseased stems often mature irregularly, with patches of brown and green tissue. In later years, infected plants develop late and produce stunted chlorotic shoots. Chronically infected plants may have small, distorted leaves with interveinal chlorosis and shoots with shortened internodes. Highly susceptible cultivars rarely survive more than 2-3 years, despite any signs of recovery early in the second growing season. Young vines succumb more quickly than do older vines. More tolerant cultivars may survive chronic infection for more than 5 years (Hewitt et al., 1942;Goodwin and Purcell, 1992).
Young shoots are stunted and bear greener, denser foliage (due to shorter internodes) than healthy trees. Lateral branches grow horizontally or droop, so that the tree seems uniform, compact and rounded. Leaves and flowers appear early, and leaves remain on the tree longer than on healthy trees. Affected trees yield increasingly fewer and smaller fruits until, after 3-5 years, they become economically worthless (Hutchins, 1933).
Trees can start showing the symptoms of variegated chlorosis from nursery size up to more than 10 years of age. Younger trees (1-3 years) become systemically colonized by X. fastidiosa much faster than do older trees. Trees more than 8-10 years old are not usually totally affected, but rather have symptoms on the extremities of branches. Affected trees show foliar chlorosis resembling zinc deficiency with interveinal chlorosis. The chlorosis appears on young leaves as they mature and may also occur on older leaves. Newly affected trees show sectoring of symptoms, whereas trees which have been affected for a period of time show the variegated chlorosis throughout the canopy. As the leaves mature, small, light-brown, slightly raised gummy lesions (becoming dark-brown or even necrotic) appear on the underside, directly opposite the yellow chlorotic areas on the upper side.
Fruit size is greatly reduced;it may take 550 affected fruits to fill a field box, compared with 250 normal fruits. The sugar content of affected fruit is higher than in non-affected fruit, and the fruit has a hard rind, causing damage to juicing machines. Blossom and fruit set occur at the same time on healthy and affected trees, but normal fruit thinning does not occur on affected trees and the fruits remain small but open earlier. Since more fruits remain, total production is not greatly reduced. On affected trees of cv. Pera and other orange cultivars, fruits often occur in clusters of 4-10, resembling grape clusters. Affected trees show stunting and slow growth rate;twigs and branches die back and the canopy thins, but affected trees do not die (Chang et al., 1993a,b;Lee et al., 1991, 1993).
Control has been achieved by removing inoculum in established orange groves and using sanitary measures to prevent infection of nurseries and new groves. All symptomatic branches from trees older than 3 years are cut off up to 1 m below the most basal symptoms. Symptomatic trees less than 4 years old are removed. To prevent the infection of nursery trees, nurseries are located away from citrus plantings, sharpshooters are controlled prophylactically by insecticides, and buds are taken from trees tested free of X. fastidiosa and grown vectors in screen houses or glass houses to exclude vectors. The effectiveness of these measures (Rodas, 1994) indicates that most spread of variegated chlorosis is from tree to tree within citrus orchards (Laranjeira, 1997).
On olives, quick decline syndrome is characterised by the development of leaf scorch symptoms and desiccation of small twigs and branches. Symptoms generally initiate in the upper part of the canopy on one or two branches, and then extend to the remainder of the crown. Severely affected plants are often pruned heavily, favouring spindly new growth which also succumbs to scorch symptoms. The tree may send out suckers from the base of the plant which subsequently die back, until the root system dies entirely (Martelli, 2016a). Grafting experiments have demonstrated that it takes at least 7 months for leaf scorch symptoms to appear on the grafted plant part (European Food Safety Authority, 2015).
Symptoms are found on all known varieties of olive. Older varieties, such as Ogliarola Salentina, Cellina di Nardò and common varieties Frantoio and Coratina, appear susceptible. It is suggested that the variety Leccino seems less susceptible, although records are based on field observations and are yet to be experimentally confirmed. Apparent variation in olive varietal susceptibility may be the result of differences in disease vector pressures in the areas where the disease is present (European Food Safety Authority, 2015).
Vector feeding causes no visible damage. Xylem feeders are prodigious feeders, consuming hundreds of times their body volumes per day in xylem sap. Most non-xylem-feeding leafhoppers produce a sugary or particulate excrement, but that of xylem feeders is watery, drying to a fine whitish powder (brochosomes) where abundant (Rakitov, 2004). The excrement of froghopper nymphs takes the form of persistent bubbles or 'froth;that surrounds the body of the insect, presumably to provide protection from natural enemies.
No grapevine (Vitis spp.) species are known to be immune to Pierce’s disease strains of X. fastidiosa, but American species used as rootstocks (V. aestivalis, V. berlandieri, V. candicans, V. rupestris) and hybrids derived from them are tolerant and some may be resistant, as is V. rotundifolia (Goheen and Hopkins, 1988). Almonds and lucerne can be hosts of the grapevine strains, but the diseases caused by X. fastidiosa in these three crop species are independent within California, USA, suggesting as yet unidentified biological differences (Purcell, 1980b). A very high percentage (75% of those tested) of crop, wild plant and weed species can carry Pierce’s disease strains of the bacterium without symptoms (e.g. wild grasses, sedges, lilies, various bushes and trees) (Raju et al., 1983;Hopkins and Adlerz, 1988;Hill and Purcell, 1995b). It is likely that in most symptomless host species, X. fastidiosa multiplies to lower populations and moves systemically less often than in pathological hosts. For example, blackberry (Rubus spp.) can be a systemic host, but the bacterium multiplies in mugwort (Artemisia douglasiana) without systemic movement (Hill and Purcell, 1995b). Hosts can be classified as propagative or non-propagative, systemic or non-systemic, and symptomatic or non-symptomatic (Purcell and Saunders, 1999b). Propagative, systemic hosts are the best hosts for efficient vector acquisition of bacteria, but vectors can acquire the bacterium from non-systemic hosts. Acquisition efficiency is proportional to the populations of live bacterial cells within plant tissues (Hill and Purcell, 1997).
Peach (Prunus persica) strains of X. fastidiosa cause peach phony disease (Wells et al., 1983), which also attacks Prunus salicina (causing leaf scald). All cultivars, forms and hybrids of peach are attacked, whether on their own roots or other rootstocks. Plums (Prunus domestica), almonds (P. dulcis), apricots (P. armeniaca) and the wild P. angustifolia were reported susceptible to phony disease before the association with X. fastidiosa was established. This reported range partly overlaps that of the grapevine-infecting strains. Various perennial weeds of orchards, such as Sorghum halepense, may act as reservoirs for the peach-infecting strain (Yonce, 1983;Yonce and Chang, 1987), but the plant host range of Prunus strains from the south-eastern USA has not been investigated extensively. Pierce's disease strains also cause almond leaf scorch disease (Davis et al., 1980), but the almond strains infect grape in low populations and without causing disease (Almeida and Purcell, 2003).
X. fastidiosa in the wide sense also causes leaf scorch in Acer rubrum (Sherald et al., 1987), Morus rubra (Kostka et al., 1986), Platanus occidentalis (Sherald, 1993a,b) (wilt and leaf scorch), Quercus rubra (Chang and Walker, 1988), Ulmus americana and Vinca minor (stunt). Strains from Ulmus and from P. occidentalis are not reciprocally infectious (Sherald, 1993a). The bacteria involved are not known to be transmissible to grapevine. Diseases of numerous woody ornamental plants in southern California, USA, including olive, date palm and rosemary, have been associated with X. fastidiosa but a causal relationship is still unproven (Wong and Cooksey, 2004). Until their relationships and pest significance have been clarified, they can all be regarded as potentially dangerous for Europe and the Mediterranean region.
X. fastidiosa causes citrus variegated chlorosis in Brazil (Lee et al., 1991;Chang et al., 1993;Hartung et al., 1994) and Argentina (Brlanksy et al., 1993). The disease affects mostly sweet oranges (Citrus sinensis);it has been observed especially on cultivars Pera, Hamlin, Natal and Valencia. It occurs on trees propagated on all commonly used rootstocks in Brazil: C. limonia, C. reshni and C. volkameriana. The disease has not been observed on C. latifolia or mandarins (C. reticulata), even when the trees were planted in severely affected orange groves (Li et al., 2000). The effectiveness of removing diseased citrus trees to prevent further spread of variegated chlorosis in citrus (Rodas, 1994) strongly suggests that most spread of this disease is from tree to tree within the crop. Control measures require the production of disease-free nursery trees in protected environments.
Citrus blight in Florida, USA, has been associated with X. fastidiosa (Adlerz et al., 1989;Hopkins et al., 1996);however the preponderance of evidence suggests that it is not the cause of blight (Derrick and Timmer, 2000).
Plum leaf scald is an important crop-limiting disease caused by X. fastidiosa from Brazil through Argentina. The South American plum leaf scald strains appear to differ from those in North America, as there are no reports of phony disease of peach in South America. The plum leaf scald strains in Brazil may have wide plant host ranges (Leite et al., 1997). A leaf scorching disease of coffee (De Lima et al., 1998) is caused by strains of X. fastidiosa that appear to be closely related to the citrus variegated chlorosis strains (Rosato et al., 1998), but its ability to cause disease in citrus (Li et al., 2001) is controversial.
In Europe and the Mediterranean region, grapevine and citrus are clearly the most significant potential crop hosts, although peach and plum are also important. Strains that cause leaf scorch diseases in oak, elm, sycamore (plane) (Hearon et al., 1980), mulberry (Kostka et al., 1986) and other tree species are also potentially damaging. Many other hosts could carry the bacterium, without necessarily being significantly affected.
X. fastidiosa has been implicated as the causal agent of olive quick decline syndrome in Europe. In 2013, X. fastidiosa subsp. pauca was associated with quick decline syndrome on olive, almond and oleander in Europe (southern Italy, Apulia region) (European Food Safety Authority, 2015). Symptomatic olive trees were often affected by multiple pests, including X. fastidiosa, several fungal species, and Zeuzera pyrina (leopard moth) (Nigro et al., 2013). Recent experimental evidence (Saponari et al., 2016) has confirmed X. fastidiosa as the causal agent of olive quick decline syndrome in Italy (European Food Safety Authority, 2016). In the USA a study evaluating olive as a host for X. fastidiosa concluded that subsp. multiplex was present but was not the cause of the leaf scorch and dieback symptoms observed on olive trees in California (Krugner et al., 2014). However, X. fastidiosa subsp. pauca has been implicated as a causal agent of olive plant dieback and leaf desiccation in Argentina (Haelterman et al., 2015). More recently, leaf scorch symptoms on olive trees in Brazil have been associated with X. fastidiosa subsp. pauca (Coletta-Filho et al., 2016).
The host range of X. fastidiosa based on the available peer-reviewed literature is presented in European Food Safety Authority (2015).
According to the European Food Safety Authority (2016), the current list of host plant species for X. fastidiosa consists of 359 plant species (including hybrids) from 204 genera and 75 different botanical families.
An erect, branched (occasionally unbranched) annual herb, green, more or less coated with white mealy pubescence. Cotyledons petiole, lanceolate-linear, mealy, bluish-grey with a reddish tinge beneath, 6–12 mm long and 1.5–4 mm broad (Korsmo et al., 1981). Roots stout and tapering at the end. Many branches may emerge from main tap root system. Epidermal cells are more or less polygonal in shape. Fewer, smaller stomata on upper compared to lower leaf surface (Srivastava, 1967). Stems erect, branched towards apex, 0.2–2 m tall, glabrous, furrowed, often with red or light-green streaks, branching varies from slight to extensive. Leaves alternate, simple ovate to rhomboid-oval, uppermost leaves mostly lanceolate, sometimes linear and sessile, glabrous, usually white with a mealy-covering, particularly on young leaves, all leaves densely covered with small, utriculate hairs. Inflorescence in irregular spikes clustered in panicles at the ends of the branches. Flower perfect, small, sessile, green;calyx of 5 sepals that are more or less keeled and nearly covering the mature fruit;petals 1;stamens 5, pistil 1, with 2 or 3 styles, ovary single-celled, attached at right angles to the flower axis. Fruits is an achene (seed covered by the thin papery pericarp). Seed nearly circular in outline, oval in cross section, sides convex, glossy, black, mean size 1.5 mm x 1.4 mm in diameter, weight 1.2 mg.
C. album seems to grow most vigorously in temperate and subtemperate regions, but it is also a potentially serious weed in almost all winter-sown crops of the tropics and subtropics. It is a common weed in about 40 crops in 47 countries, being most frequent in sugarbeet, potatoes, maize and cereals. It is one of the principal weeds of Canada and Europe, and in India, Mexico, New Zealand, Pakistan and South Africa is ranked amongst the six most serious weeds. In temperate climates, it is a problem in almost all summer- and winter-sown crops.
C. album seems to grow most vigorously in temperate and subtemperate regions, however it is also a potentially serious weed in almost all winter-sown crops of the tropics and subtropics. It is a common weed in about 40 crops in 47 countries, being most frequent in sugarbeet, potatoes, corn and cereals. It is one of the principal weeds of Canada and Europe, and in India, Mexico, New Zealand, Pakistan and South Africa is ranked amongst the six most serious weeds (Holm et al., 1977). In temperate climates, it is a problem in almost all summer- and winter-sown crops.
In subtropical regions it is most common in wheat, chickpea, barley, winter vegetables, horticultural gardens, maize, sunflower and soybean. In addition, it is an important weed of tea and upland rice in Japan, citrus orchards and vineyards in Spain, cotton, soyabean and strawberries in the former Soviet Union, cotton, pastures and peanuts in the USA, rice in Mexico and tobacco in Canada (Holm et al., 1977). In Europe and America, it is a problem weed in maize, soybean, wheat, barley, potato and all vegetable crops.
E. crus-galli is an annual grass, culms 30-200 cm, spreading, decumbent or stiffly erect;nodes usually glabrous or the lower nodes puberulent. Sheaths glabrous;ligules absent, ligule region sometimes pubescent;blades to 65 cm long, 5-30 mm wide, usually glabrous, occasionally sparsely hirsute. Panicles 5-25 cm, with few-many papillose-based hairs at or below the nodes of the primary axes, hairs sometimes longer than the spikelets;primary branches 1.5-10 cm, erect to spreading, longer branches with short, inconspicuous secondary branches, axes scabrous, sometimes also sparsely hispid, hairs to 5 mm, papillose-based. Spikelets 2.5-4 mm long, 1.1-2.3 mm wide, disarticulating at maturity. Upper glumes about as long as the spikelets;lower florets sterile;lower lemmas unawned to awned, sometimes varying within a branch, awns to 50 mm;lower paleas subequal to the lemmas;upper lemmas broadly ovate to elliptical, coriaceous portion rounded distally, passing abruptly into an early-withering, acuminate, membranous tip that is further demarcated from the coriaceous portion by a line of minute hairs (use 25× magnification);anthers 0.5-1 mm. Caryopses 1.3-2.2 mm long, 1-1.8 mm wide, ovoid or oblong, brownish (Michael, 2003).
E. crus-galli is a grass species included in the Global Compendium of Weeds (Randall, 2012) and which is considered one of the world’s worst weeds. This species has the capability to reduce crop yields and cause forage crops to fail by removing up to 80% of the available soil nitrogen. E. crus-galli is considered the world’s worst weed in rice paddies and has been also listed as a weed in at least other 36 crops throughout tropical and temperate regions of the world (Holm et al., 1991). The high levels of nitrates it accumulates can poison livestock. It also acts as a host for several mosaic virus diseases. E. crus-galli is also considered an environmental weed that has become invasive in natural grasslands, coastal forests and disturbed sites in Asia, Africa, Australia, Europe and America (FAO, 2014;USDA-ARS, 2014).
E. crus-galli can be a very serious weed in rice, maize, soya bean, lucerne, vegetables, root crops, orchards and vineyards. It has been reported to be a serious weed of 36 crops (Holm et al., 1991), particularly rice, where its similar habit and appearance make it difficult to distinguish when young.
P. hysterophorus is an erect, much-branched with vigorous growth habit, aromatic, annual (or a short-lived perennial), herbaceous plant with a deep taproot. The species reproduces by seed. In its neotropical range it grows to 30-90 cm in height (Lorenzi, 1982, Kissmann and Groth, 1992), but up to 1.5 m, or even 2.5 m, in exotic situations (Haseler, 1976, Navie et al., 1996). Shortly after germination the young plant forms a basal rosette of pale green, pubescent, strongly dissected, deeply lobed leaves, 8-20 cm in length and 4-8 cm in width. The rosette stage may persist for considerable periods during unfavourable conditions (such as water or cold stress). As the stem elongates, smaller, narrower and less dissected leaves are produced alternately on the pubescent, rigid, angular, longitudinally-grooved stem, which becomes woody with age. Both leaves and stems are covered with short, soft trichomes, of which four types have been recognized and are considered to be of taxonomic importance within the genus (Kohli and Rani, 1994).;Flower heads are both terminal and axillary, pedunculate and slightly hairy, being composed of many florets formed into small white capitula, 3-5 mm in diameter. Each head consists of five fertile ray florets (sometimes six, seven or eight) and about 40 male disc florets. The first capitulum forms in the terminal leaf axil, with subsequent capitula occurring progressively down the stem on lateral branches arising from the axils of the lower leaves. Thousands of inflorescences, forming in branched clusters, may be produced at the apex of the plant during the season. Seeds (achenes) are black, flattened, about 2 mm long, each with two thin, straw-coloured, spathulate appendages (sterile florets) at the apex which act as air sacs and aid dispersal.
P. hysterophorus is known to reduce the yield of various crops and to compete with pasture species in various countries. However, the yield loss and specific effects on the crops have not been quantified in all countries (Rubaba et al., 2017).;In Australia, the main impact of P. hysterophorus has been in the pastoral region of Queensland, where it replaces forage plants, thereby reducing the carrying capacity for grazing animals (Haseler, 1976, Chippendale and Panetta, 1994). Serious encroachment and replacement of pasture grasses has also been reported in India (Jayachandra, 1971) and in Ethiopia (Tamado, 2001, Taye, 2002). The weed is also able to invade natural ecosystems, and has caused total habitat changes in native Australian grasslands and open woodlands (McFadyen, 1992).;In India, the yield losses are reported as up to 40% in several crops and a 90% reduction of forage production (Gnanavel, 2013). P. hysterophorus is now being reported from India as a serious problem in cotton, groundnuts, potatoes and sorghum, as well as in more traditional crops such as okra (Abelmoschus esculentus), brinjal (Solanum melongena), chickpea and sesame (Kohli and Rani, 1994), and is also proving to be problematic in a range of orchard crops, including vineyards, olives, cashew, coconut, guava, mango and papaya (Tripathi et al., 1991, Mahadevappa, 1997, Gnanavel, 2013).;Similar infestations of sugarcane and sunflower plantations have recently been noted in Australia (Parsons and Cuthbertson, 1992, Navie et al., 1996), whilst in Brazil and Kenya, the principal crop affected is coffee (Njoroge, 1989, Kissmann and Groth, 1992). In Ethiopia, parthenium weed was observed to grow in maize, sorghum, cotton, finger millet (Eleusine coracana), haricot bean (Phaseolus vulgaris), tef (Eragrostis tef), vegetables (potato, tomato, onion, carrot) and fruit orchards (citrus, mango, papaya and banana) (Taye, 2002). In Pakistan, the weed has been reported from number of crops, including wheat, rice, sugarcane, sorghum, maize, squash, gourd and water melon (Shabbir 2006, Shabbir et al. 2011, Anwar et al. 2012).;In Mexico, the species is reported as a weed in cotton, rice, sugarcane, Citrus spp, beans, safflower, sunflower, lentils, corn, mango, okra, bananas, tomato, grapes, alfalfa, chili peppers, luffa, marigolds and other vegetables and fruit orchards. It is also a weed in nurseries. In Argentina is reported as a weed of tobacco fields (CONABIO, 2018).;Gnanavel (2013) also reports the following detrimental effects of P. hysterophorus on crops: it inhibits nitrogen fixing bacteria in legumes, the vast quantity of pollen it produces (ca. 624 million/plants) inhibits fruit setting, it is an alternative host for viruses that cause diseases in crop plants, and it is an alternative host for mealy bugs.
A. hispidus is sometimes considered to be perennial, as in Bhutan where it is described as ‘usually perennial’ (Noltie, 2000), but it is more commonly described as annual. It is a sprawling plant, rooting at the nodes with flowering stems up to 30 cm high;nodes hairy. Leaves are relatively short and broad, narrowly obovate up to 5 cm long and 15 mm wide, auricled at the base and acutely tipped, variably glabrous or hairy on the margins. Ligule 0.5-3 mm. Inflorescence a set of up to 10 or more racemes, up to 5 cm long, pale green or purple, variously glabrous to shortly hairy. Sessile spikelet up to 7 mm long;lower glume lanceolate, convex, 6-9-nerved with scabrid veins. Upper glume slightly longer with awn up to 11 mm long in typical forms but may be much shorter and hardly exserted. Pedicelled spikelet occasionally present at the tip of the raceme, but usually absent with pedicel a stump up to 2 mm long. Anthers 2, about 1 mm long.
A. hispidus is a sprawling grass, native to East and Southern Asia, and Africa. It has been widely introduced across North and Central America and the Caribbean, and was first recorded in the USA in the 1870s. In West Virginia and in Maryland, USA, A. hispidus is seen as a potential competitor to the endangered species Ptilimnium nodosum;Over the past decade, this aggressive grass has become widespread in many parts of the state (W. Virginia). As an annual it can compete directly…. for occupation of ephemeral habitat;without control, A. hispidus could overrun and locally extirpate P. nodosum. ’ (US Fish and Wildlife Service, 1990;1998). It is listed as an invasive weed in a number of other states of USA, such as Kentucky (Louisville Water Company, 2013). Although widespread as a weed elsewhere, it has not otherwise been described as invasive, while in Australia it is itself treated as a threatened species (Australia, 2013).
A. hispidus occurs in tea fields, orchards, grasslands and gardens, but no serious damage has been recorded. It is a weed of direct-seeded, dry-sown rice in Korea (Ku et al., 1993).
C. crepidioides is an erect, sparingly branched aromatic annual herb, 40-100 cm tall. Stem rather stout, soft, ribbed, apically with short, thick hairs, lower down glabrescent;branches densely pubescent. Leaves helically arranged, elliptic, oblong or obovate-elliptic, acute or acuminate, pinnately lobed or pinnatifid, irregularly serrate, very thinly pubescent or glabrous, 8-18 x 2-5.5 cm;base tapered and often long-decurrent into the petiole;uppermost leaves smaller, sessile. Heads in terminal, rather small corymbs, homogamous, many-flowered, cylindrical, 13-16 x 5-6 mm, nodding during anthesis, afterwards erect;bracts linear, 0.5-10 cm long, peduncles densely pubescent;outer involucral bracts free, linear, 1-4 mm long, unequal, inner ones subequal, 1-2 seriate, green with dark-brown, acute, papillose tops, lanceolate, 8-12 mm long, thinly hairy, erect during anthesis, pellucid-marginate, cohering into a cylindrical tube, ultimately spreading, reflexed;hypanthium flat, epaleate, alveolate, alveoles with membranous rim. Flowers equal, bisexual;corolla yellow throughout, 9-11 mm long, tubular;tube long, very slender, funnel-shaped, circa 1 mm long, 5-fid limb. Anthers with entire or shallowly incised base, purple, apex acute. Style bifid, arms long, thin, their truncate, more or less penicilliate top tipped by a subulate appendix. Achenes cylindric-linear, ribbed, dark-brown with paler base and apex, thinly pubescent, 2 mm long;pappus hairs numerous, thin, silky, minutely toothed, white, caducous, 9-10 mm long (Kostermans et al., 1987).
C. crepidiodes is an invasive herb included in the Global Compendium of Weeds and classified as one of the most aggressive weeds occurring in tropical and subtropical regions (Randall, 2012). It is a pioneer species with the capability to produce large amounts of hairy wind-dispersed seeds. However, Chen et al. (2009) suggest that seed dispersal ability is limited. Chen et al. (2009) report that the species has only a moderate invasive capacity and that its wide distribution in China possibly correlates with its cultivation.
C. crepidioides may be found infesting young tea plantations (Sastroutomo and Pandegirot, 1988), in rice, taro, coffee, citrus, sweet potatoes, vegetable crops, orchards and pastures.
H. brevipes is an erect annual plant up to 1 m high with a square stem typical of the family, often densely hairy but sometimes less so. Leaves are also normally coarsely hairy on both surfaces, opposite, narrowly ovate or lanceolate, 4-7 cm long, up to 2 cm wide, cuneate at the base, the margins irregularly serrate. Apex acute to acuminate. The inflorescence is a dense raceme, almost globose, up to 14 mm diameter, on a peduncle about 1 cm long in the axils of most upper leaves. Corolla white or purplish-white, irregularly five-lobed about 5 mm long. The calyx, 4 mm long, also has 5 narrow, finely barbed lobes. Bracts lanceolate, 8-12 spreading or reflexed, 4-6 mm long, almost concealed by the flowers. Seeds ovoid, up to 1 mm long, dark brown to black, obscurely striate, with a conspicuous scar.
H. brevipes is an annual plant of cultivated land and wastelands, including forest edges, wet ground and rice crops, and is favoured by continuous wet conditions, without a prolonged dry season. It is native to Mexico, the Caribbean and much of South America and has been widely introduced across South East Asia, where it has naturalized. H. brevipes may be accidentally introduced into a new area as a contaminant of seed, in particular with rice. It has been listed as a ‘principal’ weed of Malaysia and a common weed of Borneo, Philippines and Taiwan (Holm et al., 1979). In addition, PIER (2017) report that H. brevipes is invasive in Singapore, Thailand and Vietnam. Lorenzi (1982) describes it as a damaging weed of humid conditions along the coast, where it can develop into large infestations. H. brevipes is typically a weed of agricultural land, causing yield losses and a negative economic impact.
H. brevipes is primarily a weed of rice, especially in South East Asia, including Malaysia (Yong and Goh, 1977). In Indonesia it is noted to be a weed in rain-fed and upland rice fields, grasslands, rubber, cacao, young oil palm and sugar cane plantations and orchards (Knowledge Management Center on Topical Biology, 2017). It is also listed among weeds in mung bean in Indonesia (Bangun et al., 1986) and in Phaseolus beans in Brazil (Laca-Buendia et al., 1989).
N. reynaudiana is a short-rhizomatous perennial woody grass, typically 2-3 m, but sometimes taller. Culms erect, 3-10 mm diameter, with solid culm internodes. Leaf blades flat, 20-100 cm long, 8-25 mm wide. Leaf-blade surface smooth. Leaf sheaths glabrous. Ligule pilose, 1-2 mm. Inflorescence a dense, open panicle, 30-50 cm long, branches slender and nodding. Spikelets 6-9 mm, with 4-10 florets. The lower floret sterile, resembling glume and lacking a palea. Glumes subequal, 2-3 mm, acute, glabrous. Lemmas 4 mm, purplish, lateral veins conspicuously ciliate with 2 mm hairs and lemma with 1-2 mm recurved awn. Tucker (1990) noted that the species was unusual in having an abaxial (external) ligule, a cartilaginous ridge that is pilose when young.
The large stature of N. reynaudiana makes detection straightforward. Inspectors in its naturalized range should, however, be able to distinguish it from several other large grasses, including Phragmites species, Pennisetum purpureum and Arundo donax.
N. reynaudiana is a tall woody grass that has become naturalized outside of its natural range in the USA (southern Florida) and in the Bahamas on limestone-dominated substrates. In Florida, N. reynaudiana became established following planting experiments in Miami-Dade County in 1916 (Gordon, 1998). It has become widely established in at least a six-county region of the southern peninsula. The species is an aggressive invader of pine rockland habitats, but also can colonize rockland hammocks and beach dunes. N. reynaudiana is also an abundant weed of roadsides and other disturbed uplands in southern Florida. In pine rockland ecosystems the species forms dense, nearly monospecific stands, outcompeting native species. It alters fire behaviour, increases organic litter accumulation and alters succession patterns. It is known to displace a large number of endangered and rare species. N. reynaudiana was found in the Bahamas in 1974 and has since spread to at least three islands;Abaco, Andros and Bimini. In the Bahamas, N. reynaudiana is found in dry to moist disturbed areas and is a potential threat to pine rockland, coppice and coastal habitats. Eradication of N. reynaudiana is both labour-intensive and costly.
N. reynaudiana is reported to be a weed of upland rice in Thailand (Moody 1989;Galinato et al., 1999). Crane et al. (2001) lists N. reynaudiana as a common weed found in orchards in Miami-Dade County, Florida.
R. ellipticus is a stout, weakly climbing, evergreen shrub 1–3 m tall. Branchlets purplish brown or brownish, pubescent, with sparse, curved prickles and dense, purplish brown bristles or glandular hairs. Leaves imparipinnate, 3-foliolate;petiole 2–6 cm, petiolule of terminal leaflet 2–3 cm, lateral leaflets subsessile, petiolule and rachis purplish red bristly, pubescent, with minute prickles;stipules linear, 7–11 mm, pubescent, with intermixed glandular hairs;blade of leaflets elliptic or obovate, 4–8(–12) × 3–6(–9) cm, terminal leaflet much larger than lateral leaflets, abaxially densely tomentose, with purplish red bristles along prominent veins, adaxially veins impressed, pubescent along midvein, base rounded, margin unevenly minute sharply serrate, apex acute, abruptly pointed, shallowly cordate, or subtruncate. Inflorescences terminal, dense glomerate racemes, (1.5–)2–4 cm, flowers several to 10 or more, or flowers several in clusters in leaf axils, rarely flowers solitary;rachis and pedicels pubescent, bristly;bracts linear, 5–9 mm, pubescent. Pedicel 4–6 mm. Flowers 1–1.5 cm in diameter. Calyx abaxially pubescent, intermixed yellowish tomentose, sparsely bristly;sepals erect, ovate, 4–5(–6) × 2–3(–4) mm, abaxially densely yellowish gray tomentose, apex acute and abruptly pointed. Petals white or pink, spatulate, longer than sepals, margin premorse, densely pubescent, base clawed. Stamens numerous, shorter than petals;filaments broadened and flattened basally. Ovary pubescent;styles glabrous, slightly longer than stamens. Aggregate fruit golden yellow, subglobose, approximately 1 cm in diameter, glabrous or drupelets pubescent at apex;pyrenes triangular-ovoid, densely rugulose (Wagner et al., 1999;Flora of China Editorial Committee, 2015).
The invasiveness of the thorny shrub R. ellipticus has been most thoroughly documented on the island of Hawaii. Since the first report of its escape from cultivation in 1961, this species has become established in mid-elevation forest and pastureland, forming tall, dense thickets. Seeds are sufficiently viable following passage through the digestive systems of birds and mammals to readily germinate in pastureland and undisturbed forest sites where they are deposited. Several introduced frugivorous birds and feral mammals, are capable of dissemination of seeds via ingestion of the succulent fruit and birds in particular, are able to carry seeds to adjacent sites. It can also spread by suckers and resprouts vigorously after fire. The ability to colonize undisturbed native forests and displace native species is cause for alarm among resource managers of Hawaii Volcanoes National Park and other natural reserves of Hawaii, comprised of highly ecologically sensitive systems. It has been listed as one of the world’s 100 worst invasive alien species (Lower et al., 2000), and is a prohibited species in South Africa (NEMBA Category 1a).
R. ellipticus encroaches upon rice fields in China and elsewhere in Asia if farmers do not manually control this bramble. R. ellipticus invades apple, and other temperate fruit orchards in India (Misra and Sharma, 1970;Misra and Singh, 1972). Its weedy habit is particularly evident in Hawaii where it aggressively colonizes cleared pastureland and encroaches into native forests, forming tall, dense thickets.
C. aspersum is a large-sized land snail, with a shell generally globular but sometimes more conical (higher spired) and rather thin in the common form when compared to other Helicinae. The umbilicus is usually completely closed by a thickened white reflected lip that defines the peristome in adult snails. The shell is sculptured with fine wrinkles and rather coarse and regular growth-ridges and is moderately glossy because of a fine periostracum. The peristome is roundly lunate to ovate-lunate. Adult shells (4½ to 5 slightly convex whorls) measure 28-45 mm in diameter, 25-35 mm in height (Kerney and Cameron, 1979). The shell ground colour is from yellowish to pale brown. The shell also shows from zero to five reddish brown to blackish spiral bands superimposed on the ground colour and usually interrupted such that the ground colour appears as yellow flecks or streaks breaking up the bands;the bands are occasionally separated by a median white spiral line (fascia albata). Fusion of two or more adjacent bands and diffusion of band pigment on the whole shell surface are often observed. Frequently, the upper half of the shell is darker because of the effect of a dominant factor (Albuquerque de Matos, 1985). The banding pattern is much less distinct and more broken than that exhibited by the well-known polymorphic snails Cepaea nemoralis and Cepaea hortensis.
The following information is from the Canadian Food Inspection Agency Cornu aspersum fact sheet (CFIA, 2014).
Indications of an attack by C. aspersum are ragged holes chewed in leaves, with large veins usually remaining;holes in fruit;and slime trails and excrement on plant material.
Adults and larger juveniles are likely to be visible among the host material or attached to the transporting containers. They may also be hidden in protected locations, sealed into their shells to avoid desiccation. Check the undersides of containers and their rims. Small snails and eggs in soil could be difficult to find. C. aspersum hides in crevices and will overwinter in stony ground.
Inspections are best carried out under wet, warm and dark conditions. Under bright, dry conditions it is necessary to thoroughly search dark, sheltered areas where the humidity is elevated, such as under low-growing plants or debris. The snails may bury themselves in loose soil or other matter, so the only way to be reasonably sure an area is not infested is to make repeated surveys over a long period of time.
C. aspersum causes extensive damage in orchards (creating holes in fruit and leaves) and to vegetable crops, garden flowers and cereals.
In California, USA, populations established in citrus groves feed essentially on the foliage of young citrus and also on ripe fruits, creating small holes allowing the entry of fungi and decay of the fruit (see Pictures). Larger holes result in fruit dropping from the tree or being rejected for consumption during sorting and packing (Reuther et al., 1989;Sakovich, 2002).
In South African viticultural regions, C. aspersum feeds essentially on the developing foliar buds and young leaves of the vines. In kiwifruit vineyards (California, New Zealand), damage occurs on the flowers, not the fully developed fruit, since snails consume only the sepal tissue around the receptacle area. Damage to the sepals can be detrimental by increasing the development of the fungus Botrytis cinerea during cold storage of fruits, and moreover, the slime trail mucus stimulates germination of B. cinerea conidia (Michailides and Elmer, 2000).
C. aspersum, the common garden snail, is represented by several forms that are highly differentiated genetically. Only one lineage, the western one, is considered to be invasive in regions where it has been introduced recently (since the sixteenth century) either accidentally or intentionally (e.g. North and South America, South Africa, Oceania). It was in California, USA, where it was introduced in the 1850s, that it was first treated (1931) as a regulated pest. Its success in colonizing new areas after introduction and establishment may be due to: (i) large phenotypic variation in combinations of life-history traits, especially reflecting a high degree of plasticity (e.g. trade-off of egg weight/egg number), and (ii) great resistance against natural enemies. Also, genetic data indicate that C. aspersum is capable of establishing even after a severe genetic bottleneck.
C. aspersum is a polyphagous grazer with a large diet spectrum. In its natural habitat, it feeds on wild plants such as Urtica dioica or Hedera helix, which are also used for shelter. In human-disturbed habitats, a wide range of crops and ornamental plants are reported as hosts: these include vegetables, cereals, flowers and shrubs (Godan, 1983;Dekle and Fasulo, 2001). In particular, it causes serious damage in citrus groves and vineyards. It will feed on both living and dead or senescent plant material. The Host Plants/Plants Affected table does not cover all plants that C. aspersum will feed on, as the list is so extensive but aims to provide an insight to the well-known species affected. The categorization as 'Main', 'Other' or 'Wild host' is also subjective and should not be considered definitive.
Annual herb, up to 4 m tall. Stems at first densely pilosulous with short hairs, in age glabrate;leaves alternate, petiolate, the blades rather thin, ovate to triangular-ovate, mostly 7-20 cm long, acuminate, cuneate (or sometimes almost truncate) at the base and then contracted and decurrent on the petiole, simple or sometimes trilobate, the margins serrate, hispid-pilose on both surfaces, especially on the veins, scabrous, glandular-punctate beneath;heads long-pedunculate;involucres 2-3 cm broad;phyllaries biseriate, 1.5-2.5 cm long, subequal or graduate, the outer ones lance-oblong to ovate-oblong, acute or acuminate, finely pilosulous, the herbaceous apex often lax or reflexed, the inner phyllaries similar but usually shorter;ray flowers 9-13, the ligules golden yellow or orange, 2-3 cm long;disc flowers yellow, the corollas puberulent, about 9 mm long;pales acuminate to cuspidate, hispidulous above, 12-18 mm long;achenes more or less appressed-pilose or glabrous, 6-7 mm long;pappus awns 2, early deciduous, or those of the outermost flowers sometimes wanting, 3-6 mm long, the squamellae united nearly to the apex, irregularly dentate, about 2 mm long (Nash, 1976).
Tithonia rotundifolia is an herbaceous flowering plant that has been widely introduced as an ornamental and has escaped from cultivation to become invasive mostly in ruderal areas, roadsides and in disturbed sites near cultivation. In this species, traits such as its rapid growth rates, abundant production of seeds that are easily dispersed by wind, water and animals, and high germination and recruitment rates are contributing to its invasiveness and allow it to quickly invade new habitats and survive even under less favourable conditions. T. rotundifolia forms dense stands with negative impact on native biodiversity as they outcompete and displace native vegetation, alter natural regeneration and obstruct access to riverbanks (Mawela, 2014;BioNET-EAFRINET, 2018;ISSA, 2018).
T. rotundifolia is a weed of beans, chickpeas, tomato, and maize plantations. It is also listed as a weed of apple orchards and citrus plantations (Villaseñor and Espinosa, 1998;Vibrans, 2009).
The following description is from the Flora of China Editorial Committee (2017)
Medicago lupulina is an annual or short-lived perennial herb with a wide native range across Africa, Asia and Europe. It is a common weed in disturbed areas, wastelands, roadsides, abandoned pastures and forest margins. It is a nitrogen-fixing species cultivated for forage and used as a soil improver;it is also a seed contaminant of other crops. Currently, it is listed as invasive in the Philippines, Hawaii, New Zealand and a small number of islands in Oceania. However, there is limited information available about its environmental impact in these locations.
M. lupulina is listed as an agricultural weed of alfalfa, maize plantations and apple orchards (Vibrans, 2009).
M. pusilla is a perennial and annual herb, usually procumbent, many branched, 20-50 cm tall, scabrous. Stipule small, ovate-lanceolate, 4-6 × 2-3 mm;petiole 3-12 cm, stellate velutinous;leaf blade reniform, rarely 5-7-lobed, 1-3 × 1-4 cm, papery, abaxially sparsely stellate puberulent, adaxially sparsely velutinous, base cordate, margin minutely denticulate, apex rounded. Flowers usually 3-4-fascicled, axillary, rarely solitary on stem. Pedicel 2-5 cm, sparsely stellate puberulent. Epicalyx lobes lanceolate, 2-5 × 1-1.5 mm, stellate puberulent. Calyx campanulate, 5-6 mm, stellate puberulent, 5-lobed, lobes triangularly acuminate. Corolla white to pinkish, 10-12 mm in diameter;petals obcordate, 9-15 × 3-5 mm, apex notched;claw bearded. Filament tube stellate puberulent. Style branches 13-15. Fruit flat globose, 5-6 mm in diameter;mericarps 12-15, abaxially smooth, angles rounded, puberulent. Seeds reniform, approximately 1 mm in diameter, reticulate or not (Flora of China Editorial Committee, 2014).
M. pusilla is a cosmopolitan weed found principally in temperate regions of the world (Randall, 2012). It is a fast-growing, annual or perennial herb with the capacity to grow forming dense patches in gardens, yards, roadsides, waste ground, orchards, pastures and agricultural fields (Makowski and Morrison, 1989;DAISIE, 2014). M. pusilla is listed as invasive in Canada, the United States, and the Dominican Republic and in many countries in Europe (see distribution table for details;Kairo et al., 2003;DAISIE, 2014;USDA-NRCS, 2014).
M. pusilla is a weed of field crops including wheat, lentil, and flax, and in orchards and pasture lands principally in the United States and Canada (Steffey, 1980;Makowski and Morrison, 1989).
The following text is adapted from the Flora of China Editorial Committee (2015). P. arenastrum has procumbent or ascending stems, 15-30 cm tall, branched from base. Petiole is short, articulate at base. Leaf blade is elliptic or oblanceolate, 0.5-2 cm × 2-5 mm, both surfaces with conspicuous veins, base narrowly cuneate, margin entire, apex usually obtuse;ocrea white, 2-3 mm, membranous, 5-7 veined, lacerate. Flowers 3-5, grow in axillary fascicles;with narrowly ovate bracts and acute apex. Pedicel articulate at apex. Perianth is green, 5-cleft to 1/2, veined, margin white;tepals oblong. Stamens 8;filaments dilated at base. Styles 3, very short;stigmas capitate. Achenes (one-seeded fruit that does not open to release the seed) are included in persistent perianth, dark brown, opaque, narrowly ovoid, trigonous, rarely biconvex, 2-2.5 mm, densely minutely granular striate.
P. arenastrum is an annual species native to Eurasia. It is found in field and row crops, orchards, yards, gardens and turf. It readily invades areas compacted by trampling with foot traffic and is therefore frequently found along roadsides, sports fields, vacant lots, gravel parking areas and walkways. This species establishes a taproot, which allows it to survive periods of drought. As a result it can compete with agricultural crops for water and nutrients reducing yields. In California it is reported to have a negative impact on the threatened species Arenaria ursina [ Eremogone ursina ]. P. arenastrum is considered as an environmental weed in parts of Australia and an agricultural weed in cropping systems in Australia and Canada.
Smith et al. (2008) note that P. arenastrum is troublesome in agricultural fields, in particular in alfalfa fields (Medicago sativa), where soil is compacted from wheel traffic.
Description from Flora of China Editorial Committee (2017)
Themeda quadrivalvis is an annual grass found as a weed in grasslands, disturbed areas and agricultural land. It is native to the Indian Subcontinent and South East Asia but has been widely introduced to the Americas, Africa and Oceania. It is recorded as invasive in Mexico, Cuba, Dominican Republic, Reunion, Australia, Fiji and New Caledonia. It is spread unintentionally as a contaminant in straw packing, pasture seed and on vehicles and machinery. Once established, it forms dense thickets that prevent seedling establishment;this causes ecosystem change, altered fire regimes and reduced native biodiversity.
T. quadrivalvis has become an aggressive weed in sugarcane fields, citrus orchards and pastures and also in lucerne and other legume seed crops (Smith, 2002;FAO, 2017;Weeds of Australia, 2017).
Herbaceous vine, twining, 2-3 m in length. Stems cylindrical, slender, pilose or hirsute.
I. purpurea is an annual, fast growing vine widely introduced throughout the tropics where it has become naturalized and invasive. This species has a weedy behaviour that facilitates it to colonize new areas. It is included in the Global Compendium of Weeds, where is listed as an agricultural and environmental weed (Randall, 2012). In cultivated areas, the occurrence of I. purpurea results in reduced yield, along with causing difficulties during harvesting of crops (Vibrans, 2009). In ruderal areas, disturbed sites, and natural forests, it behaves as an environmental weed which has the potential to outcompete native species for nutrients, water and sunlight. It climbs using other plants for support, and grows forming a dense canopy that shades out native vegetation. I. purpurea is listed as invasive in Australia, South Africa, Namibia, Spain, China, the United States, Cuba and the Dominican Republic (Randall, 2012;Oviedo Prieto et al., 2012;Flora of China Editorial Committee, 2014;PIER, 2014;University of Queensland, 2014). It is also separately reported as present/naturalized in Malawi and as invasive in Ethiopia.
I. purpurea grows as an agricultural and environmental weed. It is listed as a common weed in maize plantations (Vibrans, 2009). In Mexico, it has been recorded as a weed in cotton, coffee, sugarcane, peppers, beans, tomatoes, potatoes, sorghum, soyabeans and fruit orchards (Vibrans, 2009).
V. villosa is a hairy, occasionally climbing, annual plant (sometimes biennial or perennial) reaching up to 150 cm in height. It has paripinnate compound leaves ending in a ramified tendril, with 5-12 pairs of narrowly elliptical leaflets;stipules eglandular. Papilionaceous flowers (butterfly-like corolla) are blue, violet, purple, or rarely white. The corolla is 10-20 mm and the limb of the standard is nearly half as long as the claw;the calyx gibbous at the base. The inflorescence is a dense raceme with 7-22 flowers;inflorescence peduncle equal or longer than the subtending leaf. The fruit is an elliptic legume 20-40 x (4-)6-12 mm, and brown when mature. There are 2-8 seeds per pod, 3 mm in diameter, often with a hilum measuring 1/12-1/5 of their circumference.
V. villosa, commonly known as hairy vetch, is now present on all continents. It is considered as native to southern and central Europe, North Africa, West and Central Asia but its native range is difficult to ascertain because of its wide naturalization after cultivation for fodder production and as a cover crop. V. villosa usually spreads from cultivation to nearby sites where it can be self-maintained. It is a potential contaminant of crop seeds and can behave as an agricultural or environmental weed. Hairy vetch can alter habitat structure and reduce the abundance of native plants through competition for space. It can also poison mammals and poultry. In California, it has been evaluated as an invasive plant but its impacts in wildlands are considered minor (Cal-IPC, 2015).
V. villosa can be a common weed in vineyards and orchards (France, Italy), in olive (Olea europaea) plantations (Spain), and croplands;affecting maize (Zea mays) (Belgium, Portugal), grain legume crops, spring-summer vegetables (Portugal), winter crops (Belgium, Germany) and rape (Brassica rapa)(Germany) (Hyppa, 2015).
F. gallica is a densely hairy and greyish erect annual, up to 33(50) cm high, with alternate leaves;capitula in clusters, surrounded by linear to linear-lanceolate involucral leaves longer than the capitula.
Filago gallica is an annual plant native to Europe, Macaronesian Islands, northern Africa and southwestern Asia. It was introduced to North America (USA, Mexico), South America (Chile), India, Australia and New Zealand, where it has naturalized. F. gallica was listed as one of the most common plants of Mediterranean origin invasive in Californian rangelands by Houérou (1991), but currently there is little information indicating its invasive behaviour. It is not recorded as a noxious or (declared) weed in its introduced range of Australia, but F. gallica can behave as an agricultural or environmental weed (Randall, 2007).
Within its native range of distribution F. gallica can be an agricultural weed (HEAR, 2015, HYPPA, 2015). F. gallica is an occasional weed of cereal crops, vineyards, olive groves and stone fruit orchards in Europe (France, Portugal and Spain) (Carretero, 2004;HYPPA, 2015).
P. perfoliata is a prickly scrambling vine. It can reach a height of 6 m or more through climbing over shrubs and understory trees. The stems are elongated, branched and furrowed with short recurved prickles along the ridges. The thin, papery leaves are triangular, about 3-7 cm long and 2-5 cm wide, glabrous on the upper surface with prickles along the mid-rib on the underside (Zheng et al., 2005). The circular, saucer-shaped leafy structures, called ocrea, surround the stem at nodes. The inflorescences are capitate or spike-like racemes up to 2 cm long with clusters of 10 to 15 tiny flowers either terminal or in the axils of upper leaves (Kumar and DiTommaso, 2005). The flowers, 1-3 cm long, are borne on racemes. The fruits are attractive, deep blue and arranged in clusters at terminals, each containing a single glossy, black or reddish-black hard seed called an achene (NPS, 2009). Roots are fibrous and shallow.
P. perfoliata is a fast growing, spiny and herbaceous vine. Like many other members of the genus Persicaria, the plant is an aggressive and/or invasive weed. The plant scrambles over shrubs and other vegetation, and blocks the foliage of covered plants from available light, thus reducing their ability to photosynthesize. The leaves, petioles, and stems of P. perfoliata contain prickles, causing the movement of wildlife, and human activities to be impacted in infested areas (Okay, 1997). In its native China the plant has been used in Chinese medicine for over 300 years (Lou et al., 1988) and has rarely been recorded as an important noxious weed in either agriculture or the environment (Wang et al., 1990).
P. perfoliata is not generally a weed of agricultural land (Wang et al., 1990), as it is removed during cultivation. However, the plant can be a pest in orchards, climbing on and covering horticultural crops. In the USA, the plant has a negative effect on Christmas tree farms, forestry operations on pine plantations and reforestation of natural areas (NPS, 2009).
The egg when first laid is translucent-white, later becoming yellow, slightly convex, round or slightly oval, measuring about 0.7 mm across. The full-grown larva has a length of approximately 12 mm, and is pink to almost red. The head, the prothoracic notum and the anal plate are brown. A black anal fork (anal comb), above the anal opening, is present.
The cocoon is a protective covering for the full-grown larva and pupa. It is made of silken threads and particles of the objects on which it rests. The pupa is reddish-brown. The adult has a wing span of 10-16 mm, and is dark-grey. When at rest, the wings are held in a roof-like position over the body, and the antennae are bent backwards over the wings. For exact identification, investigation of the genitalia is necessary.
Detailed morphology can be found in Balachowsky (1966).
The first signs of G. molesta infestation at the beginning of the growing season usually include clearly visible wilting, drying and brown lateral shoot tips (Il’ichev et al., 2003).
G. molesta causes damage of varying importance on peaches, nectarines and apricots. The larvae of the first generation are mostly found in buds and shoots of peaches, but occasionally also on shoots of apricots, plums, almonds, cherries, apples, pears and quinces. In young trees when terminal twigs are attacked, several lateral shoots will appear below them and grow rapidly. Under severe and continued attack, the tree may become somewhat bushy. Severe attacks on the rapidly growing shoots of recently budded peaches result in crooked stems.
In harvested peaches there are two distinct types of injury. One is caused by larvae that have abandoned the twigs, feeding on, or entering into, the side of the fruit early in the season when the fruit is small. It is frequently called 'old injury'. The second type of damage is caused by entrance at the stem, called 'new injury', and occurs when the fruit is almost fully grown. This injury is caused by newly hatched larvae that go directly to the fruit. The surface indications of the presence of maggots in the fruit are frequently obscure and occasionally lacking, and only a small part of such injured fruit can be detected during grading. The loss sustained by growers from this type of injury is in reduced prices for their fruit (USDA, 1958). In France, this pattern of injury is characteristically seen on nectarines. On downy-skinned peaches, the reverse may be seen (early attacks at the stalk, later attacks at the side of the fruit). G. molesta damage also favours brown-rot infection (Monilinia spp.). Fruits of other species are also occasionally attacked in the vicinity of peach orchards.
Sex pheromone-based monitoring is the most effective survey method for detecting pest insects. It can be used for early detection and warning of pest invasion, taxonomic and biodiversity investigations, population density and dispersion trends estimation, forecasting and threshold determination, mapping of pest infested areas and risk assessment, recommendation of treatments and timing of application, measuring of treatment efficacy and impact on pest density (Sexton and Il’ichev, 2000).
Timing of chemical treatments can be determined by monitoring with sex pheromone traps and accumulation of degree-days (Rice et al., 1996). Different trap designs and sex pheromone lures were compared in field trials which suggested that sex pheromone traps could be used for monitoring seasonal abundance and determining biofix dates (male catches) for phenology models (Zalom, 1994).
Fermenting brown sugar, molasses, fruit juices and port wine have been used as bait traps to attract G. molesta males and females in fruit orchards, but were not species specific and also attracted many beneficial insects and pollinators (Yetter and Steiner, 1931). The addition of terpinyl acetate to fermenting brown sugar solution traps increased the attractiveness of bait traps to G. molesta males and, most importantly, mated females.
A comparison of sex pheromone and bait trap catches over a number of seasons in Australia demonstrated that they both recorded similar infestation figures and peak moth numbers (Rothschild et al., 1984). Sex pheromone traps designed to attract males in conventional orchards are not reliable under mating disruption. However, terpinyl acetate-fermenting brown sugar solution traps effectively attract G. molesta males and females in orchards under mating disruption treatment (Il’ichev et al., 1999;Il’ichev et al., 2002).
Recently, attempts had been made to combine both traps in one and use it for monitoring of G. molesta in disrupted orchards in Argentina and conventional orchards in Chile (Cichon et al., 2012). New host-plant attractants have recently been tested to improve pest monitoring, particularly for mated females of G. molesta in orchards treated with mating disruption (Il’ichev et al., 2009;Lu et al., 2012).
A perennial erect or scandent shrub or small tree with gray or whitish trunks up to 6 cm diam, reaching heights of (2–)2.5-8.5 m. Young branchlets are hairy, pliant and often pendulous under the weight of flowers and pods. Leaflets, 4, are relatively large, hairy, bicoloured, dull or sublustrously olivaceous above and paler and sometimes subglaucescent beneath, the paniculate inflorescence terminal to branches, leafless or at base leafy-bracteate, sometimes when young appearing leafy-bracteate throughout but at maturity at least partly exserted and the primary axis then becoming abruptly zigzag or flexuous. Stipules are nearly always caduceus and small, 4.5-8(-20) x 0.4-1.3(3) mm, linear straight or falcately linear-oblanceolate acute. Leaves below inflorescence, 12-28(30) cm, petiole 1-2.4 mm diam. at middle, bluntly carinate dorsally and openly shallow-sulcate ventrally, with the sulcus widened upward to the proximal pair of leaflets, rachis glandular between proximal pairs of leaflets, with pulvinules (2-)2.5-6 mm. Racemes are solitary, 5-35-fld;flowers pale or golden-yellow, petals obovate to oblong-obovate. Sepals thinly herbaceous, greenish, yellowish, or re-flecked, the longest inner ones 8-11.5(-12.5) mm, palmately veined from base, sometimes obscurely so. Functional stamens 7, anthers of (2-)3 abaxial stamens obviously different from those of 4 median ones, their beak well over 1 mm long and porrect. Pod pendulous, cylindric, with sutures 1.2-2.6 mm wide but not differentiated externally and its valves densely granular-papillate. Pod dehiscence is follicular, before falling the valves gape to expose the seeds embedded in foetid pulp. Seeds are biseriate, turned broadside to the septa, compressed-ovid, 3.2-5.6 x 2.2-3.5 mm (Irwin and Barneby, 1982).
S. bacillaris is a shrub or small tree which has been widely cultivated across both Old and New World tropics, and can become weedy in disturbed forest, along hedges and in abandoned fields or orchards (Irwin and Barneby, 1982). Although the species does not seed well, and reportedly rarely escapes cultivation (ILDIS, 2014;Pelser et al., 2014), it possesses several traits that could indicate potential invasiveness including its ability to colonize disturbed areas and abundance in its native range. There remains a lack of invasiveness data for this Senna species which warrants further study.
D. unguis-cati is a woody vine with tendrils, 10-15 m length. Stems are cylindrical, lenticellate, up to 6 cm in diameter;cross section of the mature stem with multilobed xylem, the lobes alternating with radially arranged phloem tissue;nodes thickened;interpetiolar zone not glandular. Pseudostipules are ovate, approximately 5 mm long. Leaves are opposite, 2-foliolate, with a terminal tendril, trifid like a claw, generally of short duration;leaflets 6-16 x 1.2-7 cm, elliptical, oblong or obovate, chartaceous or coriaceous, glabrous or with punctiform scales, the apex acute or acuminate, the base acute, rounded, or unequal, the margins undulate or rarely denticulate;upper surface dark, shiny, with sunken venation;lower surface light green, dull, with prominent venation;petioles 1-4.5 cm long, petiolules 0.5-2.5 cm long, both glabrous. Flowers are solitary or in pairs, axillary;pedicel 2 cm long. Calyx is green, campanulate, 12-16 mm long, with five unequal lobes;corolla brilliant yellow, infundibuliform, 4-8 cm long, the limb 3-6 cm in diameter, with five unequal lobes, rounded;4 stamens, didynamous, inserted;ovary covered with punctiform scales. Capsule is linear, somewhat woody, brown, 25-95 cm long;seeds numerous, 1-3.5 cm long, with two membranaceous wings (Acevedo-Rodríguez, 2005).
Dolichandra unguis-cati is a vigorous, woody vine that can climb up to 15 m or higher. Due to its showy yellow flowers, it has been widely introduced as a garden ornamental. It has escaped from cultivation and become a significant invader of cultivated orchards, riparian corridors, natural forest remnants and disturbed areas, such as roadsides and urban spaces. D. unguis-cati clings tenaciously to any substrate with adventitious roots and clawed tendrils. This vigorous growth allows it to sprawl over other vegetation and, through a combination of both shading and weight, it can kill even large canopy trees. In the absence of climbing support, D. unguis-cati grows along the ground forming a thick carpet that inhibits the growth and seed germination of native understorey vegetation including native grasses, herbs and seedlings of shrubs and trees. Currently, this vine species is listed as invasive in Kenya, Malawi, Tanzania,South Africa, Australia, New Zealand, India, China, Mauritius, New Caledonia, Cuba, the Bahamas and the USA including Hawaii, Florida and Texas (Kairo et al., 2003;Henderson, 2001;Weber et al., 2008;Weeds of Australia, 2011;Oviedo Prieto et al., 2012;Randall, 2012;PIER, 2016).
The following description is from Flora of China Editorial Committee (2016)
S. alata is a shrub or small tree that is used as an ornamental and a cultivated plant throughout its range (Irwin and Barneby, 1982;PROTA, 2016). The species is reported as escaping from cultivation and becoming a weed in pastures, disturbed areas, orchards, plantations and shrublands (Irwin and Barneby, 1982;ILDIS, 2016). Livestock do not eat it, so the species has the potential to spread rapidly without control (ILDIS, 2016). It is reported as invasive in Asia (Hong Kong, Philippines, Singapore), East Africa and Oceania (Australia, Cook Islands, Federated States of Micronesia, Fiji, French Polynesia, Galapagos Islands, Guam, Hawaii, Palau, Papua New Guinea, Samoa and Tonga) (PIER, 2016). It is regarded as a significant environmental weed in the Northern Territory of Australia (Weeds of Australia, 2016). Risk assessments prepared for both Australia and the Pacific classed it as high risk (PIER, 2016).
Woody vines, twining by the petioles. Stems terete, glabrous or sparsely pubescent. Leaves simple or more often pinnatifid or pinnately lobed with up to 4 pairs of leaflets, (2-) 3.5-10(-13) x (1-)2-9(-11) cm, elliptic to broadly triangular in outline, widest in the basal third, membranous, the upper surfaces glabrous or with tiny simple uniseriate trichomes on the veins and margins, the lower surfaces glabrous;base acute, truncate or slightly cordate, occasionally oblique and asymmetric;margins less commonly entire, usually 3-7 lobed, the lobes to 5 x 2 cm, smaller basiscopically;apex acute to acuminate;petioles 1-4 cm long. Inflorescences terminal, later lateral, to 25 or more cm long, with many open, divaricate branches, with up to 100 or more flowers, glabrous;pedicels 0.8-1.4 cm, Flowers all perfect, 5-merous. Buds globose, slightly inflated, the corolla strongly exserted from the calyx tube long before anthesis. Calyx tube approximately 0.5 mm, flattened and open, the lobes 0.2 mm long, Corolla 1.1-2.5 cm in diameter, violet or pale violet, stellate-rotate, lobed ½ to 2/3 of the way to the base, the lobes 5-9 x 3-4.5 mm, spreading or slightly cupped at anthesis, densely and minutely pubescent on the tips and margins;free portion of filaments markedly unequal, the longest filament 2-3 mm, glabrous;anthers 2-3 x 1-1.5 mm, occasionally one anther slightly larger, ellipsoid, loosely connivent, yellow, poricidal;ovary glabrous;style 7-10 mm long, stigma capitate, minutely papillose. Fruit a globose berry, 0.8-1.4 cm in diameter, bright shiny red when ripe, glabrous, the pericarp thin;Seeds 4-20 per berry, 4-4.5 x 2.5-3 mm, flattened-reniform, pale yellowish tan, the surfaces minutely pitted (Knapp, 2010).
S. seaforthianum is a very aggressive woody vine with the capacity to invade natural forests, natural grasslands, forest margins, urban bushland, riverbanks, crops, pastures, roadsides, disturbed sites, and waste areas (ISSG, 2008;PIER, 2014, USDA-ARS, 2014). Plants of S. seaforthianum produce hundreds of small seeds which can be easily dispersed by birds, cattle, and by watercourses (Gallagher et al., 2010;Queensland Department of Primary Industries and Fisheries, 2011;BioNET-EAFRINET, 2014). Once established, S. seaforthianum is able to grow forming dense monocultures that overtop and smother native plant species. S. seaforthianum is included in the Global Compendium of Weeds (Randall, 2012) and is also listed as an invasive plant and/or noxious weed in China, India, Taiwan, Namibia, South Africa, Cuba, Puerto Rico and several islands in the Pacific Ocean including Hawaii, French Polynesia, and New Caledonia.
S. seaforthianum is listed as a common weed in groves, hedgerows, and waste areas in many tropical fruit orchards (i.e., lime, avocado, and mango groves) in South Florida (Crane et al., 2008).
S. halepense is a perennial grass with extensively creeping, fleshy rhizomes which are covered with brown scale-like sheaths, are up to 1 cm in diameter, 2 m in length, and often root from the nodes. The fibrous root system branches freely to depths of 1.2 m. The leaf blades, 20-60 cm long, 1.0-3.3 cm wide, have prominent midribs, are many nerved and hairless with projections on the lower surface and margins. The ribbed, hairless leaf sheaths have open overlapping margins and a membranous ligule with a hairy fringe, 2-5 mm long. Flowering stems are unbranched, 0.5-3.0 m tall, 0.5-2.0 cm in diameter, often with basal adventitious prop roots, nodes sometimes with fine hairs. The inflorescence is a pale green to purplish, hairy, pyramidal, many branched panicle, 15-50 cm long. The primary branches are up to 25 cm long, usually without spikelets for 2-5 cm from the base. The spikelets are usually in pairs but towards the top of the inflorescence they occur in threes, one spikelet of each pair or triplet is sessile and perfect with stamens and a stigma, the others are stalked and sterile or only carry stamens. The fertile spikelets are ovoid, hairy, 4.5-5.5 mm long;awns if present are 1-2 cm long and abruptly bent. The stalked spikelets are narrower, 5-7 mm long. The grain remains enclosed by glumes 4-6.6 mm long, 2-2.6 mm wide, the glumes are reddish brown to shiny black, glossy and finely lined on the surface.
S. halepense is a perennial grass which can be cultivated for fodder, but is also an extremely invasive weed with a worldwide distribution. Its extensive spreading rhizome and shoot system and high rate of seed production make it extremely invasive and difficult to eradicate. The species has a number of detrimental effects including: toxicity to grazing stock, fire risk during summer and competitive exclusion of other plants. It reduces soil fertility, acts as a host for crop pathogens and is a known allergen. It is regarded as a serious weed in 53 countries and in a wide range of field crops.
S. halepense is most commonly a major problem in subtropical crops which are planted in wide rows (cotton, maize, sorghum, soyabean and sugarcane). It can be a problem in closely spaced crops including sugar beet and wheat in warm temperate areas, and also in permanent crops, orchards and pastures.
An orchard is an intentional plantation of trees or shrubs that is maintained for food production. Orchards comprise fruit- or nut-producing trees which are generally grown for commercial production. Orchards are also sometimes a feature of large gardens, where they serve an aesthetic as well as a productive purpose. A fruit garden is generally synonymous with an orchard, although it is set on a smaller non-commercial scale and may emphasize berry shrubs in preference to fruit trees. Most temperate-zone orchards are laid out in a regular grid, with a grazed or mown grass or bare soil base that makes maintenance and fruit gathering easy.
Most orchards are planted for a single variety of fruit. While the importance of introducing biodiversity is recognized in forest plantations, it would seem to be beneficial to introduce some genetic diversity in orchard plantations as well by interspersing other trees through the orchard. Genetic diversity in an orchard would provide resilience to pests and diseases just as in forests .
Orchards are sometimes concentrated near bodies of water where climatic extremes are moderated and blossom time is retarded until frost danger is past.