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Plantwise Technical Factsheet

hazelnut blight (Xanthomonas arboricola pv. corylina)

Host plants / species affected
Corylus
Corylus avellana (hazel)
Corylus cornuta (beaked hazel)
Corylus maxima (filbert)
List of symptoms/signs
Fruit  -  lesions: scab or pitting
Fruit  -  ooze
Growing point  -  dieback
Growing point  -  discoloration
Growing point  -  lesions
Leaves  -  abnormal colours
Leaves  -  abnormal leaf fall
Leaves  -  necrotic areas
Stems  -  canker on woody stem
Stems  -  discoloration of bark
Stems  -  internal discoloration
Stems  -  mould growth on lesion
Stems  -  ooze
Symptoms
One of the most characteristic symptoms is necrosis of emerging growth from buds in late spring (Locke and Barnes, 1979; Wimalajeewa and Washington, 1980; Gardan and Devaux, 1987; Guerrero and Lobos, 1987). New growth exhibits oily lesions that start at tips and progress down emerging stems. Diseased shoots become necrotized and dry. Shoots may dry out entirely as the bacterium spreads downwards, girdling the base and causing dieback of the distal portion. Necrosis can spread to the stump and girdle the shoot, resulting in complete dieback. Black spot and streak may be found on young stems, and cankers may also be found on twigs and branches (Lelliot and Stead, 1987). The pathogen rarely causes dieback of branches or stems older than 3- to 4-years-old (Schuster, 1924; Noviello, 1969). The necrosis is only on the superficial bark and does not involve the xylem. Small, black, necrotic spot lesions are superficially present on fruits and cupules (Noviello, 1969; Gardan and Devaux, 1987). Leaves show numerous polygonal water-soaked yellowish-green to dark-green lesions, which may merge together causing a general chlorosis of the lamina and premature leaf fall (Gardan, 1986). The plants are more susceptible when young and succulent (Miller et al., 1949). Symptoms are different in orchards and nurseries. In orchards hazel is grown like other fruit trees and suckers are pruned every year. In nurseries suckering is encouraged on the mother plants to produce shoots, on which, being densely crowded, the bacteria can spread very easily. Leaf symptoms are rare in orchards, while bud cankers, dieback of new lateral shoots and cankers are frequently observed. On fruit, oily lesions are sometimes seen on the involucres and shells before lignification (Gardan, 1986). The disease may be particularly severe, causing dieback of seedlings either in the nursery or in a young orchard (Scortichini, 1995).
Prevention and control
Once established, this serious pathogen cannot be eradicated except by removal of all Corylus (hazelnut) plants. Therefore the most important element of control is to introduce only disease-free planting material into an orchard (Gardan, 1986; Gardan and Devaux, 1987). Standard hygienic practices in affected orchards such as removing and destroying affected shoots and disinfecting pruning tools may reduce the impact of the pathogen. The application of protective copper-based sprays such as copper oxychloride may be efficacious but probably must be applied annually as a prophylactic routine; when the disease is seen to be severe, it is unlikely that spray applications will be effective. Treatments with copper compounds must be done in the spring, beginning at bud break, and repeated in the autumn, at leaf fall (Gardan and Devaux, 1987; Scortichini, 1995). Spring sprays are most efficacious. The number of applications varies depending on the length of the rainy season (Noviello, 1969).

The use of resistant cultivars is recommended when planting a new orchard (cultivars NĂ©gret, Gunslebert, Segorbe, Logued'Espagne, Merveille de Bollwiller) or the species Corylus pontica (Gardan, 1986). The Graham filbert was reported as a Corylus species with a degree of resistance to blight (Brooks and Olmo, 1958). Different cultivars of hazelnut are characterized to a different degree of susceptibility, but none are immune (Noviello, 1969).

Less vigorous plants due to inappropriate cultural techniques are more susceptible to the disease. It is therefore important to avoid plantations in soil with poor drainage (Noviello, 1969).
Impact
In the USA, bacterial canker is considered to be the most serious disease of hazelnut in terms of economic importance. The greatest yield losses are seen in 1-4 year old orchards, in which up to 10% mortality has been recorded (Gardan, 1986). Losses are due to reduced yield and to the reduction in the development of young, non-bearing trees. Older plants are rarely killed. Economic losses depended on the disruption of buds and fruiting shoot, but less so on fruit lesions caused by the bacterium (Noviello, 1969). Losses in yield varied from 1 to 10% (Miller et al., 1949). In France, over 250,000 young plants have been destroyed since 1975. In 1983, 1300 ha suffered the loss of about fifty 7- to 8-year-old trees and 2 ha of 4-year-old trees were killed (Gardan, 1986).


Related treatment support
 
External factsheets
British Columbia Ministry of Agriculture Factsheets, Government of British Columbia, 2004, English language
Plant Health Australia Factsheets, Plant Health Australia, English language
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