Bramble Disease - Verticillium Wilt

The disease affects mainly black raspberries and certain cultivars of blackberries.  Red raspberries can be affected, but plants are likely to survive for several years with reduced vigor.

Symptoms

Symptoms on plants become obvious by June or early July. Shoots are stunted, and leaves, starting at the base of the infected plant, turn yellow, wilt, and drop. Black raspberry canes might show a blue or purple streak from the soil line extending upward, whereas canes of red raspberries and blackberries may show a brown discoloration. Infected ruiting canes may die as the fruit ripens. If the canes die before the fruit reaches maturity, the fruit becomes mummified, but that is the case whether the cause of cane death was verticillium wilt or something else.

Disease Cycle

The disease is caused by the fungi Verticillium dahliae and Verticillium albo-atrum, though V. dahliae may be the more common pathogen.  These fungi can exist in the soil prior to planting, and may be brought in on planting stock. The fungi can survive either in plant debris or free in the soil. The fungus enters the roots through root hairs or through breaks or wounds and moves into the vascular system, causing a systemic infection. After the plant or plant portions die, the fungus continues to survive in the soil for long periods of time. Factors that can increase disease are heavy soils and cold, wet spring weather.

Disease Management

Verticillium is favored by cool weather and is most severe in poorly drained soils following a cool, wet spring. There are no effective fungicides for management once the plants are in the ground. To minimize this disease, choose a planting site with no known history of this problem. Avoid land recently planted with tomatoes, potatoes, eggplants, peppers, strawberries, raspberries, or stone fruits; and land infested with horse nettle, ground cherry, red-root pigweed, and lambs-quarter. Plant verticillium-free nursery stock. The number of years required to eliminate verticillium, especially the resting spores from the soil, is unknown. Planting with verticillium-free black raspberry stock on uninfested soil usually ensures many years of avoidance of this disease.