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Related invasive species

  • Erwinia amylovora
Cultural Control


As is the case with most bacterial diseases, cultural practices are very important to control fire blight. These practices will tend to reduce the frequency of infections, by decreasing the potential entry of bacteria into the plant: suppression of blossoms by severe trimming of Crataegus hedges has been recommended in the Netherlands (Meijneke, 1984b);suppression of secondary blossoms in pear orchards is a proposed control measure in France (Lecomte and Paulin, 1992).
A complementary strategy for reducing the severity of infection is to follow growing practices aimed at reducing tree vigour and the duration of shoot growth (also see Chemical Control/prohexadione calcium). Restricting nitrogen and water supply to the trees is the most common advice in this respect, together with a regular pruning of the trees.
Insect control is no longer believed to be a key factor in the limitation of movement of bacteria from tree to tree. Nevertheless, care should be taken with transportation of beehives to avoid movement from an infected to a healthy orchard. Similarly, overhead irrigation should be avoided in an orchard with a history of fire blight.
Cultural methods include the sanitation of trees, obtained by a prompt pruning out of symptoms as soon as they are detected in an orchard or a plantation (Steiner, 2000). The disinfection of tools (pruning shears) with chlorine or alcohol is probably useful (Teviotdale et al., 1991) during the growing season but not in winter when trees are dormant (Lecomte and Paulin, 1991).
The early detection of symptoms is important to the success of sanitation programmes. Surveys in orchards and nurseries are recommended in spring just before bloom (active cankers), after bloom (new flower infection), in summer after hailstorms and near the end of the period of shoot elongation (shoot infections and cankers). These surveys must be followed by the removal (cutting out) of all visible infections. In most cases, warning systems will provide an indication of the most suitable period when these surveys are useful (Billing, 2000).
Risking catastrophic tree losses from rootstock blight in high-density apple orchards can be avoided only by selecting trees propagated on resistant rootstocks for new orchards. Several promising highly resistant rootstocks have been released or will soon be released from rootstock-breeding programmes (Cline et al., 2001;Norelli et al., 2003). Some of these are dwarfing rootstocks suitable for high-density orchard systems;avoiding M.9 and M.26 rootstocks in favour of resistant rootstocks is the best control for rootstock blight. Rootstock blight has not been a problem on trees propagated on Budagovsky (B.) 9 and on some Japanese rootstocks (Bessho et al., 2001;Ferree et al., 2002).
Susceptible cultivars (and rootstocks) should be avoided when establishing new orchards and ornamental planting in regions with significant fire blight problems;unfortunately, this advice is seldom followed in practice. For example, many of the most commercially successful apple cultivars introduced in recent years (Braeburn, Fuji, Gala, Ginger Gold, Jonagold, and Pink Lady) are much more susceptible to fire blight than many older cultivars and planting of these cultivars, particularly when propagated on highly susceptible rootstocks, has resulted in devastating financial losses (due to fire blight) to individual apple growers and entire apple industries (Longstroth, 2000).
Chemical Control
The number of chemicals of value for fire blight control is very limited;they belong to four categories: copper-containing compounds, antibiotics, growth regulators and elicitors.
Bordeaux mixture and fixed coppers were the first compounds used for control (Psallidas and Tsiantos, 2000). The number and timing of applications depend on the sensitivity of each cultivar to copper injury and the economic significance of the injury. Spring treatments at green tip may reduce the survival of E. amylovora around canker margins (Steiner, 2000);the value of such treatments needs to be established. More commonly, coppers are applied during bloom to prevent flower infection and in summer to prevent shoot infection.
Antibiotics (primarily streptomycin, also oxytetracycline, oxolinic acid and gentamicin) are used to prevent flower and shoot infections;they are more effective than, and not as phytotoxic as, coppers. A standard application schedule for streptomycin is two to three sprays in bloom and one to two sprays post-bloom for five sprays per year. Streptomycin has been used in North America since the 1950s and a few other countries such as New Zealand and Israel;more restrictive governmental regulation has limited and sometimes banned its use in other countries (McManus et al., 2002). Despite the selection of streptomycin-resistant strains in several countries (Jones and Schnabel, 2000;McManus et al., 2002) streptomycin use continues because alternative methods are less effective. In Israel, oxolinic acid, a synthetic quinolone antibiotic, has been used as an alternative to streptomycin (Shtienberg et al., 2001). However, strains of E. amylovora resistant to this antibiotic have been regularly isolated from Israel (Kleitman et al., 2005).
Warning systems, which provide information on risk periods (according to climate, to inoculum and to plant stages), are used in several countries for determining the need for chemical controls;timing of treatment based on warning systems often reduces the number of sprays without a reduction in effectiveness (Billing, 2000). Such systems have been developed in the USA (Thomson et al., 1982;Smith, 1993;Steiner, 2000), in Europe (Jacquart-Romon and Paulin, 1991;Berger et al., 1996;Berrie and Billing, 1997;Billing, 2000) and in Israel (Shtienberg et al., 2003). Some are available commercially. Warning systems have usually been developed for one climatic area;the use of these systems in another climatic area needs to be done very carefully, considering the influence of the different climatic parameters on the epidemiology of the fire blight pathogen (Billing, 2007).
The plant growth regulator prohexadione calcium (Apogee, Regalis) inhibits gibberellin biosynthesis and longitudinal shoot growth (Rademacker, 2000). When vegetative growth is inhibited by this regulator, it is less susceptible to fire blight (Sobiczewski et al., 2001);however, the chemical itself is not toxic to E. amylovora. In field studies, spread of fire blight during summer was reduced following the application of prohexadione calcium near the end of bloom period (Yoder et al., 1999;Costa et al., 2001). Recently, the two acylcyclohexanediones: prohexadione calcium and trinexapac ethyl, were shown to be able to reduce the incidence of fire blight on apple and pear flowers (Spinelli et al., 2007). Prohexadione calcium has been registered for growth and fire blight control in the USA and a few other countries.
Acibenzolar-S-methyl (ASM;tradenames Actigard, Bion) can stimulate the tree's natural defence mechanisms and provide a significant level of fire blight control (Brisset et al., 2000;Maxson-Stein et al., 2002). The highest level of control was obtained when sprays of ASM were initiated at the pink stage of bud development and repeated at weekly intervals, and the level of control increased as treatment rates were increased (Maxson-Stein et al., 2002). ASM was shown to stimulate the expression of pathogenicity related (PR) proteins in apple suggesting that resistance was induced through a systemic acquired resistance (SAR) pathway (Brisset et al., 2000;Maxson-Stein et al., 2002).

Has Cabi datasheet ID
21908
Detection


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.

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