Anthracnose is the most common and widespread disease of raspberries, especially black and purple raspberries; it is also often a problem on some blackberry varieties. Red raspberries are less likely to be seriously damaged, however to help ensure a disease-free planting, all management practices outlined below should be followed for all raspberry plantings.
Anthracnose first appears in the spring when the young raspberry canes are about 6 inches high. Small, purple, circular spots are found scattered over the length of the canes. These lesions soon enlarge, become sunken in the center and turn gray with purple borders (Figure 1). They eventually grow to about 1/8 inch in diameter and run together to form extensively diseased areas on mature canes (Figure 2). Anthracnose will frequently girdle the stem before the crop matures, causing the berries to dry up.
A severe outbreak of anthracnose will stunt or destroy new canes. Infected canes tend to crack during winter, causing them to dry out and break in the fruiting season. These canes are also more susceptible to winter injury.
Anthracnose is caused by the fungus Elsinoe veneta , which overwinters in lesions on old fruiting canes. Just as the raspberry buds start to open in the spring, the fungus produces spores that are carried by wind and splashing rain to healthy, young canes. The lesions that develop on these ‘spring’ canes then produce summer spores that, in turn, spread the disease to leaves, fruit, fruit stems, and fruiting canes.
Young, tender canes are highly susceptible to anthracnose infection during wet, rainy periods. During dry weather, these canes harden-off and resist the disease.
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