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) Postharvest decay is a serious problem as losses can approach 100% and may result in lower prices for the growers due to the poor quality of the fruit.
4) Cultivars that tend to retain floral structures a long time seem more susceptible.
5) Removing infected fruit before they are placed in storage can reduce the amount of postharvest decay and increase the shelf-life of stored fruit.
During wet springs, blighted blossoms become brown, with a water-soaked appearance and die. Blossoms may be covered with dense grayish powdery masses of Botrytis spores. Infections may move through the blossoms rapidly, destroying the entire floral structure. With prolonged wet weather after bloom, old flowers attached to developing berries may infect developing berries through the flower tissue. These berries develop purplish, sunken areas where the old flower has stuck. Fruit rot symptoms often are not visible until after harvest. Infected berries may not mature, or be soft and leaky. Berries may shrivel and be covered with gray mold. Twig blight infects succulent twigs turning them brown to black and later bleach to tan or gray. Black/grey spores can be found near the tip of blighted twigs. On young leaves, pale brown lesions form that may distort the leaves. Vegetative symptoms can be seen after winter injury and/or before budbreak. The disease is easily confused with bacterial blight and/or the shoot blight stage of mummyberry if there are no spores.
Botrytis is a common fungus that cannot be eliminated from fields, only reduced. The fungus overwinters as a hard black mass fungus on infected plant material, and in or on the ground. During wet springs, masses of spores are produced and carried by wind currents to new growth. Spores may also be spread by splashing water. Blossoms, twigs and fruit can be infected under periods of high relative humidity (>95%) and cool temperatures (15-20°C or 59 to 68ºF). The fungus favors tender green twigs, blossoms, leaves, and fruit. Older plant parts are rarely attacked. Twigs damaged by cold are more susceptible to infection. The fungus enters through blossoms and may remain in a dormant state until the fruit is harvested. After harvest, hundreds of spores are produced on infected fruit.
- Begin monitoring in December for twigs exhibiting botrytis die back and again starting at 3-5% bloom.
- Examine twigs for clustered grey spore symptoms and degree of Botrytis infection. Botrytis is often a secondary infection after a twig is infected by another disease, such as pseudomonas. Examine suspected damage to ensure that botrytis is the primary causal agent.
- Alert pruners to symptoms of twig infection and attempt to prune these out where possible.
- As blooms begin emerging, watch for infection which causes blossoms to turn brown in color and die. Generally blooms will be covered in characteristic Botrytis spores.
- Through fruit ripening and harvest, look for Botrytis on fruit that may be soft, shriveled, discolored, and/or covered in grey mold.