Latin name: Botrytis cinerea
Reason for Concern:
1) Under the right environmental and field conditions (wet weather during fruit development and poor circulation in the canopy) it can cause yield losses.
2) Can remain dormant and disease symptoms do not show up until after the fruit has been harvested.
3) Losses are most severe in wet weather throughout harvest.
In dry conditions, infected fruit flowers brown and shrivel. Under moist conditions, grey tufts of fungus form on blighted blossoms and on mature fruit. Fruit can appear healthy at harvest but develop rot soon after.
Botrytis is a common fungus that cannot be eliminated from fields, only reduced. Same causal agent as blossom blight and cane botrytis; the fungus overwinters on weeds, in dead leaves, mummified fruit and canes as black fungal bodies. In spring, under humid conditions, the spores infect new and mature growth via water or wind or direct contact with already infected plant parts, resulting in primocane infections through petioles. All flower parts except sepals are very susceptible. Infected new canes wilt and die. Dead canes may be covered with grey mold.
- Watch for cane infections in the spring. They may be an important source of spores for flower infection.
- Begin monitoring in December for twigs exhibiting botrytis die back and again starting at 3-5% bloom.
- Examine twigs for symptoms and degree of Botrytis infection, by variety.
- Alert pruners to symptoms of twig infection and attempt to prune these out where possible.
- Examine canes in the spring to determine the level of overwintering fungus and plan a control program accordingly.
- Wet weather during bloom promotes infection. Blossoms will discolor, and upon examining flower stamens, there will be small clusters of grey fungus.
- For risk assessment for botrytis incidence, assess: density of canopy, canes, variety, fruit rot potential.
- During fruit formation, watch for fruit with obvious grey fungal formations on them. As botrytis will occur naturally in the process of decomposition, the presence of the disease on immature fruit is of much greater concern than when it occurs only on the overripe fruit left on the canes.