In general, the adult form has white, slightly iridescent wings with a dark brown band at the outer margin and a characteristic white spot on the forewing, in the discoidal cell (Mally and Nuss, 2010). Some individuals may have a brown anal margin in the forewing and some may be entirely brown, but still show a white forewing spot. The wingspan can reach 4 cm. Adults can reach a lifespan of up to two weeks and are good flyers. During daytime, they tend to rest on the box trees or on other surrounding plants.
The larvae of C. perspectalis feed on the leaves of box trees but can attack the bark of the trees, causing them to dry out and die (Leuthardt and Baur, 2013). Typical symptoms include feeding damage on the leaf edges, with sometimes only leaf skeletons remaining. Attendant symptoms are webbing of the branches with frass and residues of moulting such as, black head capsules of different sizes. Heavy damage or repeated attacks lead to total defoliation of the trees, the subsequent attack of the bark causing the death of the tree.
Presumed virus particles mostly occur in parenchyma cells of the lesion in affected orange leaves, fruits or stems. Particles are short, bacilliform, 120-130 nm long (occasionally up to 300 nm) and 50-55 nm wide. They occur within the lumen of the endoplasmic reticulum (Kitajima et al., 1974, Colariccio et al., 1995). There is a report of similar but unenveloped particles in the nucleoplasm (Kitajima et al., 1972).;In addition to the presence of the rhabdovirus-like particles within the endoplasmic reticulum of tissues from the lesion, dense viroplasm-like material is commonly found in the cytoplasm, near the particles. Small vesicle-containing fibrillar materials are frequently present in the vacuole, associated with the tonoplast, next to the dense material (Kitajima et al., 1972, Colariccio et al., 1995).;Chloroplasts are usually affected with a disorganized hypertrophied lamella system (Kitajima et al., 1972, Rodrigues, 1995). There is a report in which rod-like particles, considered to be naked rhabdovirus particles accumulate in the nucleoplasm associated with the nuclear envelope (Kitajima et al., 1972).
Round to elliptical local lesions are seen on fruits, leaves and twigs. The severity of the lesions varies with the type of citrus and the region of origin. Leaf symptoms are usually round with a dark-brown central spot about 2-3 mm diameter, surrounded by a chlorotic halo, in which 1-3 brownish rings frequently appear surrounding the central spot, the overall lesion size varies from 10 to 30 mm, though larger lesions may form by the fusion of 2 or more adjacent lesions.;On fruits, lesions are necrotic spots 10-20 mm in diameter, with a necrotic centre. Gum exudation is occasionally observed on the lesion. On green fruits, the lesions are initially yellowish, becoming more brown or black, sometimes depressed, and reducing the market value of the fruits.;On stems, lesions may be protuberant, cortical, grey or brown. Lesions may coalesce when present in large numbers, leading to the death of the twig. In extreme cases observed in different places (JCV Rodrigues, personal communication), as described initially in 'lepra explosiva' in Argentina, severe defoliation and fruit fall may occur (Frezzi, 1940, Bitancourt, 1955, Rossetti et al., 1969).;Citrus leprosis lesions are usually very characteristic, but may sometimes be mistaken for lesions of citrus canker caused by the bacterium Xanthomonas axonopodis pv. axonopodis, or zonate chlorosis (Rossetti, 1980). Zonate chlorosis, which is associated with infestation by the same mites, does not become necrotic. Symptoms are essentially concentric green and chlorotic rings (Bitancourt, 1934).;Other viral diseases are vectored by Brevipalpus phoenicis in Brazil. Coffee ringspot virus in Coffea arabica (Chagas, 1978), Ligustrum ringspot virus in Ligustrum lucidum (Rodrigues et al., 1995), and green spot of passion fruit in Passiflora edulis (Kitajima et al., 1997). In addition, Brevipalpus californicus is a vector of Orchid fleck virus in orchids (Maeda et al., 1998). However, cross-transmission was not described among these viruses and leprosis.
Uredinia generally hypophyllous, on petioles and midribs, pustulate, orange-yellow, subepidermal, erumpent, 1-2 mm wide;uredineospores spores greyish-yellow, globose to ovoid, 26.5-43.5 x 12.5-31.0 µm, verrucose;epispore 0.5-1.0 µm thick, hyaline.
Leaves, particularly the petioles and midribs, of Rhodoendron plants from southern and central Asia, should be examined under low power magnification for the presence of telia and uredinia. A period of post-entry quarantine should be sufficient to detect latent (overwintering) infections in such plants, although it may not be completely successful (Savile, 1973;Bennell, 1985). Perennial infections may be detected by the proliferation of shoots, or “witches’ broom” symptoms.
This rust causes a “witch’s broom” of Rhododendron. Stunted shoots proliferate from infected stems. Leaves on these shoots are small, but not otherwise distorted (Barclay, 1890). Spaulding (1961) states that “it is considered to be the cause of occasional serious defoliation of spruce [ Picea ] in India and Pakistan”, but the timing of the defoliation and any symptoms preceding it are not reported.
C. himalensis is a heteroecious rust completing different stages of its life cycle on different plants. The teleomorph occurs on Rhododendron species in the Himalayan region of southern Asia;an anamorph is reported on Picea species. Although not a major problem in its narrow native range, this rust fungus could be more damaging as an invasive on Picea and Rhododendron. The fungus is a Regulated Pest for the USA;it is considered potentially damaging to Rhododendron by CAST (2002). Small amounts of perennial or latent infection may be overlooked, therefore accidental introduction of the rust could occur through importation of infected germplasm by the horticultural industry or by flower enthusiasts.
Roane (1986) lists a few Himalayan or Tibetan Rhododendron species as susceptible, but other species from that region are not reported to be susceptible. Susceptibility of the species/hybrids of other origins is not known, and many, if not most, have not been tested. Farr et al. (1996) list four host species known from China, India, and Nepal. The rust may be limited in its host range to species in certain sections of the host genus, as other Chrysomyxa species appear to be (Crane, 2005).
O. acuta is a bisexual species with multiple generations annually. This species is distinguished by the morphology of the adult female. No descriptive information on the morphology of the immature or adult male stages exists at present . The live adult females are pink and covered with a white powdery, waxy secretion. The females are uniquely found enclosed within whitish resinous cells that are open at one end, from which their pygidia protrude. The cells are usually attached to the stem at the base of the needle.
The extraction of sap by the feeding mealybugs in the area of the fascicle may lead to excessive resin flow resulting in the needles turning brown and eventually dropping off (Xu et al., 1992, Pan et al., 1994, Sun et al., 1996). High populations of the mealybug can potentially cause malformed growth, loss of plant vigour, stunting, defoliation, reduced seed production, and potential death of the plant, if not treated. The mealybugs are often found in the pitch cells located on new growth needles or on a short section of the stem immediately below the buds in the southern USA. However, the mealybugs are found completely covering the needles and shoots on pine branches in China. Heavy populations of the loblolly pine mealybug have been reported to severely damage slash pine cones that result in them being smaller than normal, deformed or crescent-shaped, and a reduction in seed production results (Sun et al., 1996). Also, the production of vast amounts of honeydew serves as a substrate for the development of sooty mould that blackens the branches, stems, and needles. These weakened trees are susceptible to attacks by other insects.
B. phoenicis is a highly variable species, but can be readily distinguished in the adult stage from the other members of the genus by having five pairs of dorsolateral hysterosomal setae and two sensory rods on tarsus II. The chaetotaxy of false spider mite is described according to Haramoto (1969).
The larvae and nymphs also have five pairs of dorsolateral hysterosomal setae, but unlike the adults they have only one sensory rod, located posteriodistally on tarsus II. Morphologically, the immature stages of B. phoenicis resemble those of B. obovatus, and like the latter they are subjected to considerable variation in size and shape of some of the dorsal setae. The number and arrangement of the setae on the dorsum of idiosoma of the larva, protonymph and deutonymph conform to those of the adult and to the genus Brevipalpus (Pritchard and Baker, 1951). Twelve pairs of setae are present on the dorsum, three pairs on the propodosoma and nine pairs on the hysterosoma. Of the dorsal setae, dorsolateral hysterosomal setae I and II and dorsocentral hysterosomal seta III are the most variable in size and shape, varying from tiny and serrate to large, broadly lanceolate and serrate, similar to dorsal propodosomal setae II and III. The number of setae on the venter is not constant but increases from four pairs on the larva, five pairs on the protonymph, seven pairs on the deutonymph to eight pairs on the adult. These additions take place in the hysterosomal regions of the body. A pair of medioventral opisthosomal setae is present in the two nymphal and adult stages but not in the larval stage. The medioventral propodosomal setae, which are present in the larval, nymphal and adult stages, and the posterior medioventral metapodosomal setae, which are present only in the deutonymphal and adult stages, are filamentous and smooth. The remaining ventral setae are smooth.
In general, the size of an individual of a stage varies according to the availability of resources (Dosse, 1952). The average size (in µm) of different stages is given below according to Nageshchandra and Channabasavanna (1974b).
Body dimensions (µm):
Egg, L 90, W 59;larva, L 145, W 102;protonymph, L 192, W 115;deutonymph, L 238, W 135;adult male, L 268, W 135;adult female, L 277, W 140.
Length of legs (µm):
Larva, I 61, II 45, III 42;protonymph, I 77, II 61, III 52, IV 56;deutonymph, I 100, II 82, III 75, IV 77;adult male, I 147, II 126, III 112, IV 130;adult female, I 142, II 121, III 114, IV 121. These values reveal that the growth of this mite is rather rapid until it reaches the deutonymphal stage, and then is more or less static. The reason might be that in the adult stage most of the food consumed is utilized for the production of eggs, whereas in the earlier stages it is used for its own growth. These mites live longer than other Tetranychid mites, but are half the size.
A diagnostic Lucid key to 19 species of Brevipalpus is available in Flat Mites of the World.
Although false spider mite is considered to be polyphagous, it is thought to cause serious crop losses on citrus (Muma, 1964;Knorr and Denmark, 1970), tea (Baptist and Ranaweera, 1955;Rao, 1970;Danthanarayana and Ranaweera, 1972;Kalshoven and van der Laan, 1981;Oomen, 1982) and papaya (Haramoto, 1969). Losses on citrus due to this mite can be enormous.
Mites belonging to the family Tenuipalpidae feed in the same way as the Tetranychidae, by continually punching the leaf epidermis with their chelicerae (Jeppson et al., 1975). The sap that oozes out of the wounded leaf cells is mixed with saliva and imbibed into the digestive tract of the mite (Haramoto, 1969). The necrotic spots are visible as a brownish, shaded area on the affected leaves, and the affected leaf can be seen filled with red coloured eggs and white empty moults (Oomen, 1982).
In tea, damage is caused by sucking sap from the stems and leaves, producing a characteristic necrotic brown spot extending along the midribs and borders of the leaves. The whole underside becomes brown, which may lead to defoliation and subsequently reduce the production of green tea leaves (Benjamin, 1968;Oomen, 1982). It is typical for affected bushes to have a thin canopy of maintenance leaves causing increased light penetration into the frame of the bush, which permits the growth of mosses and lichens. This is a traditional indication to planters that the tea bushes are in poor condition, although they are often not aware of the relation with false spider mite infestation.
On papaya plants, this mite usually feeds on the trunk at the level where the bottom whorl of leaves is attached. As intraspecific competition for food and space intensifies, the mites feed upwards on the trunk and outwards onto the leaf petioles and fruits, leaving a large, conspicuous, damaged area behind them. The immediate area around the feeding puncture becomes raised and blister-like, as though caused by a toxic substance. Later the affected tissue dries up, dies and becomes discoloured. As many punctures occur close together, the affected areas coalesce to form a large and continuous area which is callous-like, tannish and scaly and/or scabby. The feeding becomes pronounced when young papaya fruits are attacked, as the affected areas become sunken due to the differential growth of the injured and uninjured tissues. The mites sometimes puncture the latex glands while feeding, causing a copious outflow of a milky white liquid that mars the appearance of the fruits. All stages of the mite in the path of the flow of sticky latex are engulfed and drowned in it. The papaya stem, which normally remains green for a long time, becomes tannish and suberized in appearance, and makes spindly growth when heavily infested by B. phoenicis (Haramoto, 1969).
The damage caused by false spider mite is of a higher magnitude on citrus than any other crop plants, including tea and papaya. On citrus, it can cause Brevipalpus gall and halo scab with phoenicis blotch - a combination of fungus and mite attack (Knorr and Denmark, 1970;Carter, 1973). Plants attacked by the mite produce galls in the nodal region, which eventually the hinder the sprouting of new buds. The gall-like protuberances may be barely visible and woody. They look like axes that have proliferated to resemble a bud-studded cushion. No leaves develop at the axis occupied by these cushions, and when the buds are replaced by the cushions the trees become devoid of leaves and soon die. Gall formation follows the initial loss of leaves;adventitious buds sprout but are successively killed, producing hypertrophies at the bud loci (Knorr et al., 1960;Knorr, 1964;Jeppson et al., 1975). This type of symptom is common among seedlings, which ultimately die. The fungus Elsinoë fawcetti causes scab on sour orange without causing leaf drop;however, when scab lesions are also colonized by B. phoenicis, leaf drop is conspicuous. The combination of fungus and mite attack in the nursery could pose a serious problem. High populations of false spider mite are associated with a diffuse chlorotic spotting in orange trees. When such chlorotic spottings increase, they reduce the area of photosynthesis, ultimately reducing fruit production. As well as causing feeding damage, the mite transmits a viral disease caused by citrus leprosis rhabdovirus (Kitajima et al., 1972;Carter, 1973). A disease of oranges known in Argentina as 'lepra explosiva', originally thought to be caused by a fungus (Marchionatto, 1935) and later by a virus (Marchionatto, 1938;Blanchard, 1939), is now attributed to toxins injected by Brevipalpus obovatus in the process of feeding (Carter, 1952). B. phoenicis has also been collected from orange trees exhibiting these symptoms in Paraguay (Nickel, 1958).
In addition to these symptoms, B. phoenicis can cause pitting and splitting of the skin of orange fruits (Planes, 1954);scarring of tangerine fruits (Nickel, 1958);defoliation and vine dieback of passion fruit (Haramoto, 1969);and splitting of guava fruits (Nageshchandra and Channabasavanna, 1974b). It also transmits coffee ringspot virus disease on coffee (Chagas, 1973).
The first report of a host plant of B. phoenicis was Phoenix sp., a greenhouse palm (Geijskes, 1939). Since then, many different plants have been reported as infested by this species of mite in different parts of the world (Cromroy, 1958;Pritchard and Baker, 1958;Baker and Pritchard, 1960;de Leon, 1961;Rimoando, 1962;Haramoto, 1969;Nageshchandra and Channabasavanna, 1974a). Of these, Pritchard and Baker (1958) listed 63 host plant genera, and Nageshchandra and Channabasavanna (1974a) listed 35 genera in India alone. Jeppson et al. (1975) listed citrus, tea, coffee, peach, papaya, loquat, coconut, apple, pear, guava, olive, fig, walnut and grape as its principal hosts.
The live adult female is 2.9-5.0 mm long and 2.4-4.0 mm wide, with a pale yellow oval body covered in white wax or sulfur-yellow flocculent wax tinged with white. In the slide-mounted adult female, the antennae each have 9-11 segments and there are three pairs of abdominal spiracles towards the apex of the abdomen. The center of the abdominal venter becomes invaginated to form a marsupium into which the vulva opens, and there is a marsupial band of simple multilocular pores along the lip of the marsupium, which becomes sclerotized with age.
Foliage and stems should be inspected for lumps of white or yellow wax secreted by scale insects, symptoms of pest attack, attendent ants, sticky honeydew and sooty mould growth on leaves. A user-friendly, online tool has been produced for use at US ports-of-entry to help with the identification of potentially invasive scale insect species (Miller et al., 2014a,b).
Most damage to plants is caused by the early immature stages of I. samarai, which feed on the leaf undersides, settling in rows along the midrib and veins, and on smaller twigs. The older nymphs feed on larger twigs, and as adults they settle on larger branches and the trunk. Damage to plants results from phloem sap depletion during feeding, leading to shoots drying up and dying. Trees that are badly attacked suffer partial defoliation and a general loss of vigour. The insects dischargesugary honeydew, which can be copious in large colonies and may foul plant surfaces. Besides direct damage by feeding, indirect damage can result from the development of black sooty mould on the honeydew on leaf surfaces, blocking light and air from the plant, leading to a reduction in photosynthesis (Beardsley, 1955).
The scale insect Icerya samaraia (formerly Steatococcus samaraius) occurs in the Australasian, Oriental and Oceanic zoogeographic regions. It has a wide host range which includes mostly woody plant species in 40 genera belonging to 25 families. It is a minor pest of citrus, banana, coconut, guava, papaya, cocoa, pigeon pea and other plants, including forest and ornamental trees. Populations of I. samaraia are apparently being kept under control on the Palau Islands in the western Pacific Ocean by natural enemies, particularly by the introduced coccinellid Rodolia pumila. I. samaraia can be transported on infested plant materials because of its small size and habit of feeding in concealed areas, making it a potential threat as an invasive species.
I. samaraia has been reported on mostly woody plant species in 40 genera belonging to 25 families from the Australasian and Oriental zoogeographic regions (Miller et al., 2014a).
Detailed descriptions and illustrations of F. auricularia are provided by Crumb et al. (1941), Behura (1956), and Lamb and Wellington (1975).
F. auricularia is primarily a nocturnal species, hiding during daytime in dark places, where it tends to aggregate. Its presence in the agricultural environment can easily be established by looking under loose bark, stones, pots, wooden boards etc., or by providing artificial hiding places such as upturned flower pots filled with straw or cardboard. Using corrugated cardboard rolls or bands on trunks of trees or grapevines is an easy way to detect earwigs in orchards and vineyards. They can be easily seen on crop edges and on trees and vines when active and feeding at night (Department of Agriculture and Food, Government of Western Australia, 2015).
Despite the considerable size of last instars and adults detection is difficult in shipments. With vegetables, a sample will need to be cut open in order to reveal any hiding earwigs. Sometimes submergence of fruits and vegetables (e.g. cauliflowers) in cold water will drive earwigs out. Frequently they hide in the cores of apples and pears, in which case their presence can often be detected through frass and some external damage around the remnants of the calyx through which they usually enter the inside..
It is also difficult to detect contamination with earwigs in bulk loads, timber and balled up or potted plants.
F. auricularia is a polyphagous generalist feeding on a wide range of crops, particularly fruits, vegetables and flowers. Most of the damage observed is caused by external feeding, resulting in partially destroyed or shredded plant parts. Feeding on tender plant parts often results in underdeveloped or malformed crops. On hops, earwigs have been observed to feed on young tender leaves (Theobald 1896). In corn (Zea mays) they feed on tender kernels but greater damage is caused by feeding on the silks, which leads to underdeveloped grains (Crumb et al., 1941). Sugar beets and mangels are damaged by feeding on both the roots and leaves (Lind et al., 1914, Lind et al., 1916). Cabbage varieties such as Savoy or cauliflower are prone to be affected by earwigs through direct feeding on the leaves, tunneling into the cabbage heads, and hiding and feeding inside. Other crops reported to be affected are peas, beans and tomatoes (Capinera, 2013). Occasionally, defoliation of potato plants takes place (Frank, 1896). Serious damage to seedlings is reported from cabbage, carrot and cucumber (Crumb et al., 1941). In flower production earwigs cause damage by feeding on various parts of the plants. Seedlings and flower buds are particularly affected, resulting in deformed blossoms (Crumb et al., 1941). There have been reports of earwigs damaging flowers of fruit trees such as plums (Theobald, 1896). In New Zealand, earwigs have been of economic concern by eating into peaches, nectarines and apricots rendering them useless for sale and in Chile damage to ripening cherries is problematic (Tillyard, 1925;Devotto et al., 2014). In Australia cherries are particularly affected;earwigs either eat directly into ripe fruits or damage the stalks of ripening cherries (Department of Agriculture and Food, Government of Western Australia, 2015. Damage to ripe apples and pears is sometimes reported (Capinera, 2013).
The European earwig, Forficula auricularia, is a polyphagous insect that is native to large parts of Europe and western Asia as far east as western Siberia. In the early twentieth century it was accidentally introduced into North America where it became widespread in a number of states/provinces of both the USA and Canada. It has also invaded Australia and New Zealand, and more recently Mexico, Chile and the Falkland Islands. Although economic damage to vegetable and flower gardens is generally minor, when high population densities occur it is a major pest in gardens and greenhouses, and a significant nuisance in households. Within and sometimes also outside its native range it is also regarded as a beneficial organism used or encouraged as a biological control agent to control other insect pests in orchards and gardens.
F. auricularia is extremely polyphagous and has been reported to cause damage on a wide range of crops, in particular vegetables, flowers and stone fruits. Damage is mainly caused by external feeding of late instars and adults. Vegetables are mostly affected by external feeding externally on leaves, stems and stalks, and sometimes by penetrating the inside of crops such as cabbages and cauliflowers or feeding on seedlings and young plants (Frank, 1896;Lind et al., 1914, Lind et al., 1916;Crumb et al., 1941;Baker, 2009;Weems and Skelley, 2010;Department of Agriculture and Food, Government of Western Australia, 2015). In addition a wide variety of fruits can be affected by earwigs, with damage to stone fruits such as cherries, nectarines, peaches and apricots being more prevalent compared to apples and pears (Theobald, 1896;Tillyard, 1925;Crumb et al., 1941;Department of Agriculture and Food, Government of Western Australia, 2015).
In vineyards damage is caused by feeding on tender leaves, shoots and fruits (Huth et al. 2009;Department of Agriculture and Food, Government of Western Australia, 2015). The biggest problem with F. auricularia in vineyards is, however, their presence in harvested berries and the risk of tainting wine (Department of Agriculture and Food, Government of Western Australia, 2015).
The species can cause significant damage to flower production with dahlias, pinks, carnations, sweet William, zinnias and roses most frequently cited (Crumb et al., 1941;Weems and Skelley, 2010). Hops can be affected by feeding on tender leaves and shoots (Theobald, 1896). Among staple crops, damage has been reported from potatoes and corn (Frank, 1896;Coyne, 1928;Hearle, 1929;Eckstein, 1931;Weems and Skelley, 2010).
Detailed descriptions have been supplied by Walker (1983), Simpson et al. (2006) and Pegg et al. (2014) and in reviews by Coutinho et al. (1998) and Glen et al. (2007). Lesions mainly appear on young, actively growing leaves and shoots, but also on flowers and fruits. Often the first sign of infection is chlorotic flecks on leaves and shoots, followed by the production of masses of bright yellow urediniospores;more rarely yellow-brown teliospores are produced, often intermingled with urediniospores. Lesions often turn red-purple then grey with age, and often have a purple or dark brown margin. Lesions tend to be angular in shape, extending through the leaf, and more often coalescing. Uredinia are 0.1-0.5 mm diam., amphigenous, yellowish (but fade to pale tan when old), more common and larger on the abaxial surface, subepidermal becoming erumpent and up to 500 μm. Urediniospores vary from globose, ellipsoidal to ovoid and obpyriform, are yellowish, 14-27 x 14-29 μm, finely echinulate, with or without a tonsure;germ pores have not been observed. Telia are 0.1-0.5 mm diam., subepidermal to erumpent, abaxial, pulvinate and yellowish-brown. Teliospores are 22-50 x 14-28 μm, cylindrical to ellipsoidal, with a rounded apex, yellowish brown, 2-celled, constricted at the septum and pediculate. Basidia are cylindrical, up to 110 μm long, 6-8 μm wide, hyaline, 4-celled, produced from each cell of the teliospores, apically in upper cell and laterally in lower cell. Basidiospores are globose to pyriform, 8-11 μm, hyaline and smooth.
The primary symptom of myrtle rust is the appearance of yellow pustules (uredinia) on the upper and lower leaf surfaces of Myrtaceae, with more tending to be found on the lower surface. Pustules can also be found on stems, fruit and flowers. Slightly darker mustard-coloured pustules may indicate the teliospore stage of the fungus. After 1-2 weeks, the pustules begin to turn pale grey. From this stage, it is difficult to distinguish rust lesions from insect damage or other necrosis.
A. psidii attacks young, soft, actively-growing leaves, shoot tips and young stems. Fruit and flower parts are also susceptible. The first signs of rust infection are tiny spots or pustules. These symptoms can appear 2-4 d after infection. Symptoms can vary depending on the host species, susceptibility level within a host species, and age of the host leaf. After a few days, the pustules or uredinia erupt with the production of distinctive, yellow urediniospores. The infected area spreads radially outwards and multiple pustules eventually merge and coalesce with age. Secondary infections can occur within days but are usually confined to new young tissue, shoots and expending foliage. Left untreated, the disease can cause deformed leaves, heavy defoliation of branches, dieback, stunted growth and even plant death.
Austropuccinia psidii is a rust fungus with a wide and expanding host range within the Myrtaceae, with over 440 host species currently known (Carnegie and Lidbetter, 2012;Morin et al., 2012;Pegg et al., 2014). Like many rusts, urediniospores of A. psidii can be wind-dispersed over long distances. Viable spores have been detected on clothing and personal effects following visits to rust-affected plantations (Langrell et al., 2003), and this is a viable pathway for dispersal. Furthermore, there are several instances of (accidental) long-distance movement of A. psidii on diseased plants, both within and between continents (Loope et al., 2007;Kawanishi et al., 2009;Carnegie and Cooper, 2011;Zambino and Nolan, 2012). Under sub-optimal conditions, the rust can remain un-symptomatic within plants for more than a month (Carnegie and Lidbetter, 2012). This combination of wide host range and ease of long-distance dispersal make A. psidii a successful invasive pathogen. It has spread quickly once established in new countries, including Jamaica (MacLachlan, 1938), Hawaii (Uchida and Loope, 2009), Australia (Carnegie and Cooper, 2011;Pegg et al., 2014) and New Caledonia (DAVAR Nouvelle-Calédonie, 2014). Severe impact on a range of Myrtaceae has been recorded in amenity plantings, commercial plantations and the native environment. A. psidii was first identified as an invasive pathogen in the 1930s when it caused extensive damage to allspice (Pimenta dioica) plantations in Jamaica (Smith, 1935;MacLachlan, 1938). A. psidii has been identified as a quarantine risk for some time in many countries including Australia (Australian Quarantine Service, 1985;Grgurinovic et al., 2006), South Africa (Coutinho et al., 1998) and New Zealand (Kriticos and Leriche, 2008).
Carnegie and Lidbetter (2012) provide the most recent published host list for A. psidii, based on extensive searches of overseas records (see references therein) as well as the then current host records from surveys in Australia obtained from State Government agencies. The taxonomy of Myrtaceae is in a constant flux, with accepted naming of genera and species often controversial (even within a country). Carnegie and Lidbetter (2012) use the classification according to Govaerts et al. (2011), and as such altered original published host names to fit this classification where necessary (providing synonyms for many). The Australian records have since increased based on host testing (Morin et al., 2012;Sandhu and Park, 2013;F. Giblin, University of the Sunshine Coast, Queenland, Australia, unpublished data, 2014) and increased detections during field surveys (Pegg et al., 2014), with new hosts also from New Caledonia (DAVAR Nouvelle-Calédonie, 2014). This brings the current global host list for A. psidii to 445 species, in 73 genera and 16 tribes of Myrtaceae. A proportion of these hosts are known only from host testing. For example, in Australia there are 346 host species (56 genera) known (Carnegie and Lidbetter, 2012;Morin et al., 2012;Pegg et al., 2014), with approximately 116 of these known only from host testing (Morin et al., 2012;Sandhu and Park, 2013;F. Giblin, unpublished data, 2014).
For reasons of space, the Host plants and Other Plants Affected table in this datasheet lists only the genera affected and the species for which full datasheets are included in Compendia.
The most highly susceptible species recorded to date are Syzygium jambos, Eugenia reinwardtiana, Agonis flexuosa, Gossia inophloia, Melaleuca quinquenervia, Rhodamnia rubescens, R. maideniana, R. angustifolia, Chamelaucium uncinatum and Decaspermum humile (Pegg et al., 2014) and Rhodomyrtus psidioides (Carnegie and Cooper, 2011).
The small hairy larvae of U. lugens feed gregariously on the upper and lower epidermis, the pallisade tissue and the spongy mesophyll of the leaf but avoid the oil cells and the veins. This feeding habit results in the leaf being ‘skeletonised’, hence the common name of the insect. Larger larvae, from the fifth instar, feed individually and consume the entire leaf blade down to the mid-rib (Cobbinah, 1978). From around the fifth instar, U. lugens larvae retain their moulted head capsules on top of their head, creating a distinctive ‘head dress’. Larvae spin a camouflaged pupal cocoon incorporating their own hairs and fragments of surrounding materials. Adult moths are approximately 10 mm in length with a wingspan of 25 to 30 mm. The forewings are dark grey with several dark wavy lines connecting front and rear wing margins (Anonymous, 1979). The hindwings are pale grey-brown.
U. lugens can be detected by searching leaves. Eggs are laid in batches on the leaf surface, and young larvae feed gregariously adjacent to the egg batch after emergence. Oviposition tends to occur mainly in the lower crow of the tree (Morgan and Cobbinah, 1977). Young larvae skeletonise the leaves, making leaf damage easy to detect. Skeletonised leaves often have characteristic patches of cast skins where larvae have moulted before moving on. After the fifth instar larvae disperse and can be found singly, often in the vicinity of abandoned skeletonised leaves. When close to pupation, larvae wander in search of a suitable site. Camouflaged cocoons are formed in the bark or leaf litter and are very difficult to find. A synthetic pheromone has been developed, and can be used for detection and delimiting surveys (Suckling et al., 2005).
Early instar larvae skeletonise leaves, which then turn brown, giving the tree a scorched look when damage is heavy. Older larvae feed on the entire leaf blade down to the midrib, which can resemble defoliation.
U. lugens was first considered a serious pest of natural eucalypt forests in Western Australia in 1983 when the first severe outbreak occurred there (Strelein, 1988). Prior to that it was widely known as a pest of eucalypt forests in eastern Australia (Campbell, 1962;Harris, 1974). As these natural forests are or were managed for timber production, it is considered an economically important pest in its native range. Damage to amenity trees is also a common problem, although few trees are killed by this defoliation (Anonymous, 1979).
Morgan and Cobbinah (1977) list 149 Eucalyptus species and one Angophora species found to be oviposition hosts, out of more than 250 species surveyed in a field study in Adelaide, South Australia. Not all of the oviposition hosts proved to be suitable larval hosts. That work was part of a wider study in which over 580 tree species were surveyed (Cobbinah, 1978). Significant defoliation events have occurred in natural forests of Eucalyptus camaldulensis, E. calophylla and E. marginata in mainland Australia (Campbell, 1962;Strelein, 1988;Farr, 2002), and in plantations of E. nitens in Tasmania (Anonymous, 1994) although damage is common on a wide range of eucalypt species. E. nitens and E. fastigata are important commercial plantation and farm forestry species in New Zealand, although commercial impacts of U. lugens on these species have yet to be felt. The iconic native species Metrosideros excelsa (pohutukawa) has been recorded as a host in New Zealand, although this seems to only occur through spill-over feeding from near by eucalypts (Potter at al., 2004) and is not significantly impacting these trees. A number of other new host records have occurred in New Zealand since U. lugens arrived in that country, most notably on a range of deciduous Northern Hemisphere species. The most significant damage on these species has occurred on Betula pendula (silver birch), where some trees have been defoliated (J Bain, Scion, Rotorua, New Zealand, personal communication, 2008).
In New Zealand, U. lugens has been recorded on 58 tree species (J Bain, Scion, Rotorua, New Zealand, personal communication, 2008), mainly from the genus Eucalyptus. It is causing significant damage in New Zealand on Lophestemon confertus, which is commonly planted as a street tree in some parts of Auckland. In a laboratory study of larval suitability of 18 highly valued eucalypt species in New Zealand, Potter and Stephens (2005) found E. nitens, E. nicholii and E. fastigata were most at risk.
Pheromone-baited traps are the primary method for detecting and delimiting new isolated gypsy moth populations in previously uninfested areas. Pheromone-baited traps are a very sensitive tool that can be used to detect very low density populations that could not be detected using any other method. Every year, over 300,000 traps are deployed in the USA for detection/delimitation alone (Tobin et al., 2012). When a new population is detected using pheromone traps, it is a common practice to make a search for gypsy moth life stages in order to confirm the presence of a reproducing population. However, given the difficulty of detecting low-density populations in this way, life stages cannot always be found in all populations.
Larvae on foliage are easily distinguishable from other defoliators. Late in the year, host pupae and egg masses on tree trunks indicate gypsy moth infestation. Egg mass counting is a common practice for monitoring infested areas to estimate population density and predict future outbreaks. In North America, the detection of gypsy moth outbreaks is also based on aerial defoliation surveys.
Hatching larvae usually start feeding on flushing buds and later on newly-expanded leaves. High populations often result in total tree defoliation, often across a large spatial area.
The gypsy moth is likely to ultimately occupy virtually all portions of the temperate world where oaks and other suitable host plants occur. Consequently, the northern hemisphere is more at risk for establishment than the southern hemisphere though some suitable hosts do occur in these areas. The gypsy moth is apparently not able to persist in very cold (e.g. Finland) or warm (subtropical to tropical) regions.
The gypsy moth is a 'proven' invader. The broad range of host plants that it utilizes (Liebhold et al. 1995), along with its high reproductive rate combine to make this insect a very successful invader of many types of forest and urban landscapes. Another characteristic that contributes to the gypsy moth's invasiveness is its propensity to be transported on human-made objects (e.g., egg masses can be laid on vehicles, logs, etc.). Perhaps the greatest limitation this species has as an invader is that females (of the European strain) are incapable of flight and this limits its rate of unassisted range expansion. However, as females of the Asian strain are capable of flight and all strains can lay their eggs on human-made objects, established populations are nevertheless able to spread.
Main hosts are defined as those that can be consumed by all gypsy moth instars without loss in developmental rate, developmental success, and adult fitness;other hosts are defined as those that can be consumed by some gypsy moth instars (often later instars) but with negative impacts, such as reduced developmental rate or reduced fecundity as adults. For a full list of main hosts, other hosts, and plants that have been shown to be non-suitable hosts, see Liebhold et al. (1995).
The genus Calacarus is a distinctive group of mites, as the females usually have a purplish body and three or five longitudinal wax-bearing ridges on the opisthosoma (Lindquist et al., 1996;Anon., 2014). Wax may also occur on the dorsal shield, following the dorsal shield lines (Lindquist et al., 1996). The rostrum of the female is relatively large and curves downwards (Huang, 2014). The coverflap of the female mite is 32.2 to 36 µ wide and 19.8 to 21.3 µ long, with many faint, short lines (Huang, 2014).
C. carinatus causes a bronzing or purple discolouration of infested leaves (Mamikonyan, 1935;Anon., 2014). Infested leaves also have a ‘dusty’ appearance due to the cast skins of the mites and the residue of ‘mite wax’ on the leaf surface (Anon., 2014). The white skins and wax on the upper leaf surface can be seen using a hand lens (Anon., 2014). Leaves attacked by the mites turn completely brown and dry up, and defoliation occurs in heavy infestations (Shiao, 1976;Vazquez, 1991).
C. carinatus causes a bronzing or purple discolouration of infested leaves, hence the common name ‘rust mite’ (Mamikonyan, 1935;Anon., 2014). This is more apparent on the leaf margins (Shiao, 1976). Infested leaves also have a ‘dusty’ appearance due to the cast skins of the mites and the residue of ‘mite wax’ on the leaf surface (Anon., 2014). Leaves attacked by the mites turn completely brown and dry up, and defoliation occurs in heavy infestations (Shiao, 1976;Vazquez, 1991). The mites usually attack older leaves and show a preference for the upper surface, especially along the midrib and margins (Light, 1927).
C. carinatus is a mite native to Asia. It is now also present in Africa, Europe, the USA and Australia. It usually attacks camellias and can reduce tea leaf production. In Kenya, C. carinatus has resulted in loss of capital due to the reduction in tea leaf production.
C. carinatus usually attacks camellias, but has also been found attacking Spathiphyllum plants in Florida greenhouses (Anon., 2014). It is said to have an unusually wide host range compared to other members of the genus, apart from Calacarus citrifolii (Lindquist et al., 1996). In addition to attacking Camellia sinensis, it has also been reported from Camellia japonica and ‘two hosts in two other dicot families’ (Lindquist et al., 1996). Other hosts include: leaves of Viburnum opulus in California, USA;Capsicum annum in Mauritius (Moutia, 1958);and Camellia kissi and Camellia caudate in Assam, India (Das and Sengupta, 1962).
Mycelium: The mycelium is composed of branched, septate, olivaceous brown to brown hyphae (1-3 µm wide). On the host, the fungus colony is hypophyllous and maculicolous. The stromata may be poorly developed on leaves, but well developed on fruit shucks (husks) and twigs (Gottwald, 1982;Partridge and Morgan-Jones, 2003;Schubert et al., 2003).
Pecan scab is relatively easily detected based on visual inspection for characteristic symptoms of the disease on the foliage, fruit and shoots of its host (Nolen, 1926;Demaree, 1924, 1928;Littrell, 1980;Goff et al., 1996). Characteristic symptoms include dark black spots of scab with a velvety appearance on the surface of the affected organ.
F. effusum affects the fruit, stems, leaves, dormant buds and catkins (Nolen, 1926;Demaree, 1924, 1928;Littrell, 1980). Defoliation and nut drop can occur if infection is severe. The symptoms are similar on all infected plant parts.
On the leaves, dark brown to black spots of scab can be observed on both the abaxial and adaxial surface of the lamina shortly after bud break, and are often associated with the veins or midrib. Spots vary in size from 1 to 7 mm in diameter, which can coalesce into larger spots. When young, the spots have a velvety appearance. As the infection ages, it turns hard and forms a dark grey or silvery to brown spot that extends through the leaf. These senescent spots can crack and drop out of the leaf, resulting in a shot-holed appearance on older leaves. The leaf lesions are a source of inoculum for the young fruit (Nolen, 1926;Demaree, 1928;Schubert et al., 2003).
Small, olive-green to black spots can develop on the young fruit early in the season. If conditions are favourable, the lesions can increase in size, coalesce and cause large areas of disease, often with a velvety appearance while the lesions are young. If the lesions are particularly large the surface can become brown and cracked. If infection is very severe and the pathogen penetrates deeper it can cause the shuck (husk) to cling to the shell of the nut. The spots may be slightly raised. On fruit, black fungal stromata may form on the spot, which can produce a dark, velvety growth of conidiophores the following spring (Nolen, 1926;Demaree, 1928;Schubert et al., 2003).
On the shoots or twigs the symptoms are similar to those on the leaves or fruit. The edges of the lesions may be slightly raised, with dark fungal growth in the centre. Twig lesions may also form stroma and overwinter, producing conidia the following spring, similar to those zone the fruit shuck (husk) (Nolen, 1926;Demaree, 1928).
Symptoms on the pedicels and bracts of the catkins and on dormant buds are reported to be slight and typified as small, black spots (Demaree, 1924).
F. effusum is a fungal pathogen that causes pecan scab, which can result in severe economic losses on susceptible cultivars and resulting harm to the pecan industry in areas with high rainfall where pecan is grown. The disease develops on leaves, fruits and shoots and results in loss of photosynthetic area and reduced fruit size and quality. Pecan scab can also lead to reduced fruit set in the following year due to plant stress. Fungicides used to control pecan scab are costly. It is introduced to new areas through movement of infected host material. Despite quarantine restrictions, it is likely that human-mediated transfer has occurred between the native habitats in south-eastern USA and Mexico, and locations where pecan is grown as an exotic in South America, South Africa and New Zealand. F. effusum overwinters as stroma and conidia in lesions on shoots and fruit shucks, and the conidia are dispersed in wind and rain splash. The pathogen is a threat to all pecan-growing regions with a humid, wet environment.
From an economic viewpoint pecan (Carya illinoinensis) is the most important host. The other susceptible species are wild hosts in the same genus as pecan (Carya) that occupy similar habitats in the USA (Schubert et al., 2003;http://nt.ars-grin.gov/fungaldatabases). There are reports of its occurrence on Carpinus spp., but the causal agent in now considered a separate species (Schubert et al., 2003). There is an unconfirmed report of F. effusum causing disease on Juglans regia from Brazil (Mendez et al., 1998). No other species are reported to be hosts, or susceptible to infection by F. effusum.
Adults are small sawflies, almost entirely dark brown other than pale, yellow to white legs and palps. The summer and winter generations may be distinguished by the length of the genae (Blank et al., 2010).
A. leucopoda is best detected as a feeding larva on leaves, the ‘zigzag’ browsing traces being easily recognisable as this is the only species known to produce such feeding damage on elm. Leaf-miners on elm feed within the leaf and may be mistaken for A. leucopoda, particularly the species producing more chaotic mines (e.g. Stigmella spp.), though these do not chew through the entire leaf. Once found, mature larvae can be swiftly identified by looking for T-shaped marks on thoracic legs 2 and 3 and a transversal lateral dark stripe between the stemmata. Adults are harder to find, though if captured they can be keyed out through Blank et al. (2010). The lattice-like pupal cocoons are also distinctive and can usually be found on the underside of leaves. Eggs and overwintering cocoons, particularly if the latter have fallen to the ground, are more difficult to detect. Adults are known to fly to yellow sticky panel traps often used for monitoring other sawflies, which should be a suitable method for detecting adults (Vétek et al., 2016).
Looking for the 'zigzag' feeding pattern of young A. leucopoda larvae on elm trees is the most used method for detecting the species. If found, larvae can then be keyed through using Blank et al. (2010). Older larvae often eat over the original feeding trace, obscuring it (Vétek et al., 2017). The lattice-like pupal cocoons are also distinctive, usually being found on the underside of leaves. Heavy infestations may lead to extreme defoliation, but the 'zigzags' should still be visible, along with pupal cocoons.
Elm zigzag sawfly is considered a minor pest within its native range in East Asia, but since first arriving in Hungary and Poland in 2003 the sawfly has spread rapidly through Europe and is continuing to expand its range. Severe localized defoliation has been recorded by the species throughout Europe on elms in a variety of situations. Most elm species are utilised as host plants, which combined with it being both parthenogenic and multivoltine means populations can build up rapidly in suitable areas. No specific predators are known, and whilst parasitoids have been described on the species in Europe no studies have investigated their efficacy at controlling elm zigzag sawfly. This species was removed from the EPPO Alert List in 2015 following no international action on the species being requested by the EPPO member countries.
Reviews of elms (Ulmus spp.) in botanical gardens have revealed a number of species attacked by A. leucopoda which are only rarely planted through Europe, plus others which have not been attacked (Blank et al., 2014;Vétek et al., 2017). However, some of these records are hampered by small sample sizes (n=1 in some cases);subsequent work may find that such species are eventually attacked by A. leucopoda. Nevertheless, localized host preferences have been detected, such as an apparent aversion to Ulmus laevis in Germany (Blank et al., 2014) and in Poland (Borowski, 2018), despite this being a host tree elsewhere. Zúbrik et al. (2017) found U. laevis to be fed upon by A. leucopoda but recorded no evidence of the species on U. glabra. This may be due to climatic differences between the regions in which U. glabra grows within Slovakia, as U. glabra is an important host elsewhere (Blank et al., 2010;Csóka et al., 2012;Vétek et al., 2017). Elms can often be hard to identify to species level, which along with the genus’s complicated taxonomic history means that there may be occasional issues with host identification and differences in the names reported.
Successful development by A. leucopoda on non- Ulmus species has not been reported. Papp (2018) showed that whilst females will lay eggs on Zelkova serrata and Hemiptelea davidii (both Ulmaceae) larvae appeared not to complete development. There is thus no evidence that either species is a true host for A. leucopoda.
Significant wild hosts include Ulmus 'Lobel', Ulmus 'New Horizon', Ulmus 'Rebona', Ulmus 'Regal' and Ulmus 'Resista'.
P. pittieriana is a microcyclic (short cycle) rust that produces only teliospores and basidiospores.
There are no records of transported contaminated crop produce causing spread of P. pittieriana. The only risk of spread is by the transport of infected plants or plant material, which is usually prohibited. Field-grown potatoes [ Solanum spp.] from highland areas in countries where this disease is known should not enter international trade. There is no need for detection and inspection procedures if appropriate transport restrictions are observed.
Lesions begin as minute, round, greenish-white spots that grow up to 3-4 mm diameter on the underside of leaves. Some lesions become elongated with their longer axes reaching 8 mm. They later become cream, with reddish centres that turn tomato-red and finally rusty-red to coffee-brown. The lesions protrude by 1-3 mm, with corresponding depressions on the upper leaf surface, and may be surrounded by chlorotic or necrotic halos. Defoliation results when hundreds of lesions form on a leaf. Elongated or irregular lesions occur on petioles and stems;fruits and flowers are also affected (French, 2001a).
P. pittieriana is a microcyclic rust fungus occurring on potato [ Solanum tuberosum ], tomato [ Solanum lycopersicum ] and wild species of Solanum in South and Central America and is an EPPO A1 quarantine organism for Europe (EPPO, 1988). Probably capable of causing disease on potatoes in cool, moist regions of the temperate and tropical zones, this fungus can be transported in fresh or dried plant material or crop debris in soil. As the basidiospores are short-lived and not produced in large numbers, the fungus is not spread far by natural agents such as the wind.
Field observations were made on cultivated tomato [ Solanum lycopersicum ], cultivated potatoes (Solanum tuberosum subsp. andigenum and subsp. tuberosum), and the wild potato, Solanum demissum. All other records of susceptibility listed are the results of greenhouse tests (Reddick, 1932;Buritica et al., 1968).
P. pittieriana affects the following cultivated and wild potato species in greenhouse tests:
- Cultivated potato: Solanum ajanhuiri, Solanum curtilobum, Solanum juzepczukii, Solanum phureja, S. tuberosum subsp. andigenum and S. tuberosum subsp. tuberosum.
- Wild potato species: Solanum antipoviczii [ Solanum stoloniferum ], Solanum cardiophyllum, Solanum commersonii, S. demissum, Solanum ehrenbergii, Solanum gibberulosum, Solanum famatinae [ Solanum spegazzinii ], Solanum malinchense [ Solanum stoloniferum ], Solanum oplocense, Solanum parodii [ Solanum chacoense ], Solanum schickii, Solanum simplicifolium [ Solanum microdontum ], Solanum stoloniferum and Solanum verrucosum (Buritica et al., 1968).
- Other species of Solanum affected are Solanum caripense and Solanum nigrum in Colombia (Buritica et al., 1968).
Conidiophores comprised of a stipe, sterile stipe extension with a terminal vesicle, and penicillate arranged branches bearing phialides. Stipe septate, hyaline, 95-155 µm, the stipe extension terminating in a broadly ellipsoid vesicle, vesicle apex pointed to papillate, 6.5-11.0 µm diameter, the widest part above the middle. Primary branches 0-1-septate, (5-)15-41(-66) x 3-5 µm, secondary branches aseptate, (11-)13-25(-35) x 3-5 µm, tertiary branches rare. Terminal branches bearing two to five phialides. Phialides reniform, hyaline, aseptate, (10-)13-18(-21) x 2.5-5.0 µm. Conidia cylindrical, straight, hyaline, 1-septate, the ends rounded, 42-68 x 4-6 µm, in slimy clusters. Chlamydospores on carnation [ Dianthus caryophyllus ] leaves dark-brown, thick-walled, forming microsclerotia. Reverse of colony on malt extract agar (MEA) fuscous black at centre fading through sienna outwards. Mycelium at margin white. For additional details, see Henricot and Culham (2002).
This pathogen causes dark leaf spots, dark streaks on the stems, and eventual defoliation of Buxus species. Conidiophores bearing clusters of distinctive large cylindrical conidia and a vesicle-tipped sterile stipe extension are produced on shoots incubated in a moist chamber at 20°C (Henricot and Culham, 2002).
The fungus causes dark-brown leaf spots, which may coalesce to cover whole leaves, black streaks on stems that appear to progress from the bottom of the plant to the top, and severe defoliation and dieback (Henricot et al., 2000, 2008;Henricot and Culham, 2002).
C. pseudonaviculata is an asexual species in a genus of common ascomycete plant pathogens. It was identified relatively recently in the UK, as an introduced species causing a devastating shoot blight of boxwood [ Buxus spp.] plants that are commonly used in gardens and landscaping. The full extent of its host range is not known, but Buxus spp. from different continents were found to be susceptible (Henricot et al., 2008). It was placed on the EPPO Alert list in 2004, as it appeared to be spreading to the mainland (EPPO, 2009a), and removed from the list in 2008. This pathogen has been reported from additional European countries in recent years, and may have been transported in asymptomatic infected plants or propagating materials. It survives well in plant debris and probably also in soil.
The disease has only been found in some cultivars of three species out of the 91 in the genus Buxus worldwide: B. sempervirens, B. microphylla and B. sinica var. insularis (Henricot et al., 2008). When detached stems of other species, including plants native to four continents, were tested beside these, Henricot et al. (2008) found no immunity to the fungus. Differences between the species were not consistent in tests with different isolates of the pathogen. The lowest level of disease was observed in B. balearica, B. riparis and a Sarcococca sp. Sarcococca is a genus in the Buxaceae that includes some species imported for use as ground cover;Pachysandra species, also members of the family often used for ground cover, were not tested (Henricot et al., 2008).
Conidiophores solitary, fasciculate, or forming loose synnemata 12-45 µm wide, unbranched, septate, smooth, pale-brown to brown, (60-)120-240 x 4.5-7 µm, usually arising from a dark stroma, 30-60 µm diameter.
The lower sides of leaves should be examined for the dark sporulation of the fungus in grey to brown sunken lesions with yellow halos;the lesions are also visible from the upper surface (Kuate, 1998). Mature fruits also bear sunken brown lesions with a yellow halo, with sporulation occurring under wet or humid conditions.
On leaves, the fungus produces circular, mostly solitary spots, which often coalesce, up to 10 mm in diameter, with a light-brown or greyish centre when dormant and non-sporulating during the dry season, but becoming black with sporulation after the onset of the rainy season (Sief and Hillocks, 1993). The lesions are usually surrounded by a dark-brown margin and a prominent yellow halo;occasionally the centre of the lesion falls out, creating a shot-hole effect. At first glance, the young lesions appear similar to those of canker (caused by Xanthomonas campestris pv. citri), but differ in being flat or shrunken. Leaf spots, especially on younger leaves, often coalesce and together cause generalized chlorosis, followed by premature abscission and defoliation of the affected tree. Young leaves and fruit appear to be more susceptible than older mature leaves (Sief and Hillocks, 1999), but whether the leaves or fruit are more affected varies with the host species and variety (Bella-Manga et al., 1999) and location (Derso, 1999).
On fruit, the spots are circular to irregular, discrete or coalescent, and mostly up to 10 mm in diameter. On young fruits, infection often results in hyperplasia, producing raised tumour-like growths surrounded by a yellow halo;these develop central necrosis and collapse (Kuate, 1998). Lesions on mature fruit are normally flat, but sometimes have a slightly sunken brown centre. Diseased fruits ripen prematurely and drop or dry up and remain on the tree (Kuate, 1998). Infection by the fungus seems to predispose the fruit to secondary infection by Colletotrichum gloeosporioides (De Carvalho and Mendes, 1952;Seif and Kungu, 1990);it is common to find a dark-brown to black sunken margin of anthracnose around the fruit spots.
Stem lesions are not frequent and mostly occur as an extension of lesions on the petiole. Occurrence of several such lesions at the stem tip results in dieback;those on other parts of the stem coalesce, become corky, and crack. At the base of the dead stem there is usually a profuse growth of secondary shoots (Menyonga, 1971).
P. angolensis is a dematiaceous hyphomycete occurring in sub-Saharan Africa and Yemen. This fungus requires moisture for infection and the production of wind-borne conidia and causes a devastating fruit and leaf spot disease of cultivated species of Citrus. Losses of 50-100% of yield can occur and growers may cease production where the disease is endemic. Although species and cultivars of Citrus vary in susceptibility, no source of resistance is known (Kuate, 1998). An A1 quarantine pest for Europe and the Mediterranean region (EPPO, 2009), this fungus is also of concern for other warm humid regions where citrus is grown, such as Florida, USA. Other than by wind, conidia can be transported on infected fruit or propagated material.
All species of cultivated Citrus appear to be susceptible, although the lime (Citrus latifolia) and smooth lemon (Citrus limon) are often reported to be relatively resistant. Of the other members of the Rutaceae in Africa, Citropsis tanakae is known to be infected (Kuate, 1998). The susceptibilities of the many wild Citrus species in Asia (USDA-ARS, 2009) remain unknown.
All stages of the life cycle occur on one host. Spermagonia and aecia have been observed in Greece (Grigoriou, 1992) and Iran (Hamzeh-Zarghani and Bani-Hashemi, 2002). In Pileolaria, spermagonia are flat and subcuticular, and the structures and spores of aecia resemble those of the uredinia (Hiratsuka et al., 1992).
Cinnamon-brown uredinia appear on the undersides of leaf spots and on fruits in the spring and summer. Dark mounded telia develop on the upper side of leaves in summer and autumn.
Small orange-red to purple spots, often somewhat angular, and usually more visible on the lower side of the leaf, expand and may coalesce before becoming necrotic and dark-brown. Uredinia develop in spots on leaves and on fruit clusters;infected fruit is malformed (Smith et al., 1988), with or without visible leaf spots, dark masses of teliospores develop in scattered or confluent pustules, primarily on the upper surface of leaves. Severe infection due to significant rain at the end of the winter and beginning of the spring can lead to defoliation (Assaweh, 1969).
P. terebinthi is an autoecious rust, completing all stages of its life cycle on trees in the genus Pistacia. It occurs on native species from the western Mediterranean to mainland China and northwestern India, but has not been reported from native species or the introduced pistachio tree in North America. Introduction to other pistachio-growing areas has not occurred. The importation of infected trees or cuttings would facilitate this. No evidence exists that the commercially-traded nuts could carry the pathogen from infected fruit. Locally, the fungus is distributed by windborne basidiospores, aeciospores, urediniospores and fallen leaves bearing teliospores.
In a breeding nursery, Corazza and Avanzato (1985) found that Pistacia vera was more severely attacked by rust than was Pistacia terebinthus, whereas Pistacia atlantica showed no symptoms of infection. Hamzeh-Zarghani and Bani-Hashemi (2001) report variation in severity depending on age and sex in Pistacia mutica. Pistacia chinensis and Pistacia weinmannifolia are reported as hosts for both species of rust, P. terebinthi and Pileolaria pistaciae, in China (Tai, 1979;Teng, 1996;Chen, 2002).
The process of leaves falling off a plant, or of making this happen: