Latin name: Colletotrichum gloeosporoides and C. acutatum
Reason for Concern:
1) The primary concern is reduced shelf life and poor quality fruit for the fresh market.
2) This disease appears on fruit before harvest (ripe rot) and as a postharvest fruit rot, but control tactics must be implemented earlier in the season.
3) Pruning and the destruction of prunings from the field does not reduce primary inoculum and has little impact on the resulting disease.
4) The cultivars such as Bluecrop, Blueray, Bluetta, Earliblue, Herbert, and Spartan are very susceptible while the cultivars Collins, Elliot, and Weymouth are considered resistant.
Berries do not develop symptoms until they are mature or almost mature. The initial symptoms are shriveled, sunken areas near the blossom end of the berry. As the disease progresses, the fungus produces wet salmon to orange colored masses of spores on fruit surfaces which become more apparent on harvested fruits. New shoots and leaves may also become blighted in spring. Heavy infections on flower buds and young twigs can cause shoots and blossoms to turn brown to black color. Stem cankers are rare, but brown to black sunken lesions of 1/8" in diameter with raised margins can appear on stems under favorable conditions
The pathogens overwinter in or on live twigs and flower buds, and also on dead twigs, spurs and fruit. Dead fruit cluster stems appear to be the main site where the fungus overwinters. In the spring, the fungi produce spores which get splashed onto flowers and developing fruits mainly by rain and overhead irrigation. The pathogen requires a minimum of 12 hours of continuous leaf/berry wetness when temperatures are between 15 to 27°C (52 to 80° F) for infection. Berries are susceptible to infection at all stages in their development, though berry infections are only obvious when fruit is mature, the fruit tissue may be infected anytime from flowering to harvest. After the fungus enters the developing fruit it remains dormant until the berry starts to ripen. Then it produces enzymes that destroy plant cells. Damaged cells deflate and the entire area becomes shriveled. Spent fruit cluster stems can be infected after harvest. Infection can occur anytime, though wet conditions favor disease spread and build up.
- Largely based on crop history. When scouting, examine 4 locations in a 10 acre plot, sample ten clusters per bush and record the number of clusters with visible signs of sporulation, sample at least 5 plants per location.
- Watch for the blighted shoot tips and/or flowers turning brown or black.
- Leaf spots, when they occur, are roughly circular.
- As infected berries ripen, the flower end may soften and pucker.
- Under warm and rainy conditions, salmon-colored spore masses form on infected berries.
- After harvest, spore masses form rapidly on infected fruit when in cellophane-covered baskets or in plastic clamshell packs.