Apple
Botryosphaeria Dieback
Botryosphaeriaceae
Fungus
In a Nutshell
- Cankers or streaking often develops in parts of the bark that were wounded during field work.
- Cross-sections of the trunk show wedge-shaped dark brown lesions that reach the core of the wood.
- Shoots, foliage and buds can also be affected.
Apple
Symptoms
This is mainly a wood disease that results in cankers and dieback symptoms on the trunk. Cankers or streaking often develops in parts of the bark that were wounded during field work, for example pruning. A cross-section of the trunk shows wedge-shaped dark brown lesions that reach the core of the wood. Shoots have a stunted appearance and can also be affected by dieback. Bud development is delayed or stopped, with the internal tissues undergoing necrosis. Graft failure is also characteristic of this disease. These symptoms do not always occur together and in some varieties, there are no foliar symptoms at all. Overall, the disease decreases the cultivars' productivity and longevity, reduces yields and increases production costs.
Recommendations
Organic Control
A certain degree of biocontrol can be reached through the use of formulations of species of Trichoderma fungi (for example a mixture of T. sperellum and T. gamsii). This helps to protect pruning wounds, basal ends of propagation material and grafts before infection. A number of organic products are available for pruning wound protection.
Chemical Control
Always consider an integrated approach with preventive measures together with biological treatments if available. Fungicides, paints and pastes containing tebuconazole, cyproconazole, fluilazole can be directly applied onto large cuts as soon as possible after pruning. Other fungicides include fludioxonil, fluazinam, flusilazole, penconazole, iprodione, myclobutanil, and pyraclostrobin.
What caused it?
The symptoms are caused by a group of fungal pathogens of the family Botryosphaeriaceae. They infect a wide range of hosts but are most commonly associated with woody plants. The fungi overwinters on the bark of infected vines or trees and start producing spores during the spring. Spores are spread via wind and rain splashes to other vines. They enter the tissues through fresh injuries such as natural cracks, pruning wounds or cuts where they can germinate at temperatures above 5 °C. Early pruning during the dormant period of the vine makes the wound more susceptible to disease. They gradually invade the vascular tissue of the trunk and thread their way to the roots. This results in the formation of cankers, wood necrosis and dieback of the trunks. Alternative hosts include cork oak, poplars, cypresses and junipers.
Preventive Measures
- Grow less susceptible varieties.
- Keep the vineyard clear of plant residues and dead wood.
- Avoid pruning during wet weather and minimize number of wounds.
- Mark diseased wood and remove branches or entire vines.
- Prune later in the dormant period to avoid the peak of spore production.
- Extra irrigation may help manage symptom severity but avoid overhead irrigation.
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