Hazelnut Disease Management
Last updated on September 24, 2019Young orchards are susceptible to diseases, including EFB. The new hazelnut varieties are already showing susceptibility to diseases, not previously known to occur in British Columbia such as Phomopsis, and Phytophthora sp. Therefore, young orchards must be protected, by adopting Best Management Practices
Diseases
Eastern Filbert Blight
Eastern filbert blight (EFB) on hazelnut is caused by the fungal pathogen Anisogramma anomala. Vigour and productivity decline significantly when trees are infected with this fungus, resulting in an economically unproductive orchard. EFB has become a common and serious disease in hazelnut orchards throughout the Pacific North-Western United States and southern part of British Columbia.
Symptoms
Infected trees may show sudden dieback of twigs and branches in summer months. When closely observed, elongated, sunken cankers, expanding lengthwise on branches can be seen. Cankers are infected areas of sunken, dying tissues formed along a branch. Dark-brown to black coloured spore producing structures called ‘stroma’ are produced within cankers in relatively straight rows lengthwise along the branch. Cankers expand from year to year and girdle the branch, resulting in branch dieback. The disease also resembles another fungal disease caused by Eutypella cerviculata. Eutypella produces similar spore producing structures; however, they are smaller in size and produced on dead wood.
Biology
In spring, spores are released from stroma produced on mature cankers on infected hazelnut trees. Spores are spread by rain and splashing water droplets driven by wind. Young and developing shoots, during bud break to shoot elongation, are highly susceptible to new infection.
Newly infected trees do not show any symptoms for 12-15 months (latent period). The second summer following infection, the pathogen begins to produce stroma within cankers on infected stems (an important diagnostic feature in field and laboratory). The mature stroma begin releasing spores the following spring. The pathogen continues to produce new stroma and releases spores as the canker expands each year.
Identification and Monitoring
Monitoring: As EFB continues to spread within and around commercial orchards, orchards must be scouted intensively. Control of EFB will be much more effective if the disease is detected early. Scouting should be done twice a year. In late summer, look for dying branches (dieback). In the dormant season (late fall and winter), look for the cankers and stroma; mostly found near the top of the canopy. Suspicious samples can be submitted to the Ministry of Agriculture Plant Health Laboratory or other plant diagnostic laboratories for disease confirmation.
Management
Prune out any diseased branches with cankers about 2-3 feet below the site of infection and burn diseased wood. Alternatively, infected wood can be chipped, covered with plastic film and allowed to compost. This must be done before bud-break in spring. Because initial symptoms are often found in the top of trees, it is best to use a “cherry picker” to gain better viewing during scouting for disease and access for pruning out infections.
Preventative fungicide sprays are essential to help prevent new infections and slow down the progress of the disease; particularly young orchards of new varieties must be protected from EFB. Since new growth in spring and early summer is highly susceptible to infection, spraying must begin soon after bud-break. A maximum of 4 applications at 10-14 day intervals, from bud-break to new shoot growth, is considered necessary to provide adequate protection. The fungicides registered for EFB are included in the Table 7. It is essential to set up the sprayer to obtain adequate coverage of all new growth. Because of EFB’s latent period, the effect of fungicides on disease control will only be evident years after application.
Bacterial Blight
This disease is caused by the bacterium Xanthomonas arboricola pv. corylina (also called Xanthomonas campestris pv. corylina). Losses due to this disease are most commonly seen in young, establishing trees less than 6 years of age or in stressed trees.
Symptoms
Leaves can develop necrotic spots (usually less than 3 mm in diameter) that are reddish-brown and surrounded by a yellowish-green zone. The symptoms can also appear as small, dark brown or black spots on the green nut, although this is quite rare.
Bacterial blight can cause lesions which encircle the trunk of young trees and cause them to die. These lesions can be difficult to detect, but close examination shows the bark to be slightly sunken and reddish-purple in colouration. If you remove the bark at the crown with a knife, the tissue beneath is brown. A sticky liquid containing bacterial cells may ooze out of the lesions during periods of high humidity, and dead leaves will generally cling to the girdled trunks for some time. Blighting or dieback of infected branches can occur on trees of any age. Dieback results in reduced yields.
Biology
The bacterium overwinters in infected buds and other plant tissues, which then ooze from cankers during the growing season. Bacterial cells are spread throughout the growing season by rain splash, infected nursery stock or contaminated pruning tools. The bacterium enters trees through natural openings or wounds on the plant. It survives from one season to another in cankers and infected buds, survival is better in the large branch and trunk lesions than in the smaller twig lesions (less than 8 mm in diameter). It generally does not attack and kill branches that are more than 3 years old.
Note that temperatures above 20 oC favour infection, although infection can occur at lower temperatures if the period of wetness is long enough. Wet weather is an important factor in the spread of bacterial blight. The pathogen from cankers is carried by water droplets onto branches below the cankered branch. Moisture must be present on the plant tissue for infection to occur, but the infection time can be as short as one hour for leaf infections if the leaf is wet during that period. Disease incidence also seems to increase following freezing weather. This may be because the trees are weakened, or because there may be more entry sites through wounds.
Identification and Monitoring
Scout young orchards regularly. Identification of the pathogen is the first step in controlling this disease. Sometimes bacterial blight can be confused with other diseases such as sunscald and winter damage, but laboratory testing can confirm the presence of the bacterial pathogen. It is easiest to test for the bacterium during the spring. Buds can be infected but may not show symptoms for over 200 days. This means that healthy looking trees can be already infected. All young trees (including planting stock) should be handled and treated as though they were infected
Management
Prune out infected branches below the canker lesions in the winter to reduce sources of inoculum. Burn or bury infected material and sanitize pruning tools after working on each tree.
Chemical control: It is important to protect young orchards. Chemical sprays are recommended in late August and early summer before the first heavy rains. If rains are heavy, apply bactericides (Table XX) during the fall when75% of leaves have dropped and in the early spring when the buds are opening.
Emerging Diseases
Besides EFB and Bacterial blight, new hazelnut varieties, particularly young orchards can become susceptibility to new diseases, not previously known to occur in British Columbia.
Preliminary studies conducted in 2017 by the BC Ministry of Agriculture shows that some of the young orchards of EFB-resistant hazelnut varieties are showing symptoms that are related to Phomopsis and other foliar pathogens, and Phytophthora, a root pathogen. Some commonly observed symptoms and the pathogens associated with them are included in Table 6.
| Emerging Diseases | Description of Symptoms | Management |
|---|---|---|
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Phomopsis canker (Phomopsis sp.) |
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Phytophthora root rot (Phytophthora sp.) |
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Pesticides in Agriculture
Integrated Pest Management