Latin name: Elsinoe veneta
Reason for concern:
1) Occasionally affects blackberries.
2) Serious if rains continue late into spring; cane spots may retard sap flow, thus girdling canes.
3) Uneven berry ripening may result from infected canes.
Initial infections typically occur on lower cane portions toward the inside of the plant but can also affect leaves and fruit. The first symptom is small, purplish or reddish circular patches on the cane. As they enlarge, the central portion grays, sinks and cracks. Margins raise and purple. Damaged patches are often so clustered that they merge, forming large, irregular areas. Canes eventually girdle and die. Leaves and leaf stems may show various degrees of purple spotting, depending on plant variety. Berries may ripen unevenly and have abnormally small drupelets.
Cause: a fungus spread by spores produced in the small black bodies that form in gray patches in the fall. In winter, the fungi overwinter on infected canes. In spring, splashing rain carries spores to infect new shoots, leaves or fruit.
- Slashing spores that overwinter on old canes usually begin cycle in the spring. Watch for sunken grey areas with purple raised margins on floricanes in the spring when primocanes are emerging.
- First lesions usually show up on the lower parts of the canes--redish, sunken, round spots. They then enlarge to grayish spots with a purple margin that can girdle canes. The floricane is most commonly infected from 6 to 24 inches above the ground.
- Leaves can sometimes show purple spotting.
- In very severe outbreaks and/or very susceptible varieties, the fruit may have small, uneven druplets.
- Scout 4 areas of the field with 20 plants per area, count plants with lesions. Record the total number of plants with lesions.