Many raspberry and blackberry plantings were infected with diseases this past year due to high rainfall in May. Root rots were prevalent in plantings with heavy soil, as well as anthracnose on canes, leaf spots, and botrytis fruit rot when left uncontrolled. Now is the time to plan for the next growing season and to consider using cultural practices that reduce overwintering diseases.
This winter begin by inspecting bramble plants for any lesions or desiccated areas on canes and shriveled dead fruit that failed to mature. If disease symptoms are few, pruning out last year’s fruiting canes may sufficiently reduce the overwintering disease inoculum. Next, thin the canes that will bear fruit in 2016 to ensure rapid drying of foliage during the next growing season and reduce new infections. If diseases were severe last year, all canes can be pruned at the soil surface and removed from the planting. Although this will eliminate or reduce fruit harvested in 2016, it will disrupt the disease cycle of some pathogens. During pruning, also remove nearby wild brambles in adjacent woods or hedgerows as these plants can be sources of viruses.
Another way to minimize bramble diseases is to install trickle irrigation. Inexpensive kits can be purchased with in-line emitters in tubing that deliver water at the soil surface. This type of irrigation system reduces leaf wetness which promotes disease infection. Alternatively, purchase a nozzle for the hose that produces a flat fan pattern of water rather than a wide cone pattern. When irrigation is needed, water only the base of the canes rather than wetting the foliage.
During the growing season, prune out infected plant tissue as soon as symptoms are observed and dispose of the infected material rather than leaving it near the planting where reinfection may occur. Also, when fruit is ripe, harvest berries daily to prevent fruit drop. Rotting berries left in the planting can be a source of reoccurring disease infection.
When it is time to consider replanting, select plants from a reputable nursery. Before purchasing or accepting a shipment of brambles, inspect the foliage for any defects and do not accept any plant material with visible disease symptoms. If purchasing plants by mail, immediately notify the company and reject them as they should be certified as disease-free. When locating a new bramble planting, avoid a site where other raspberries, blackberries, strawberries, elderberries, gooseberries, currants, stone fruits, tomatoes, peppers, or other Verticillium-susceptible plants have been grown previously. Verticillium is a soil-borne pathogen that causes wilting, dieback, and can kill many different plant species. For a list of Verticillium susceptible plants, see http://www.missouribotanicalgarden.org/gardens-gardening/your-garden/help-for-the-home-gardener/advice-tips-resources/pests-and-problems/diseases/cankers/verticillium-wilt.aspx. Soil fumigation or soil solarization can be used to eliminate this disease, but these are not always feasible methods of control.
Once the new site is located, consider planting raspberries on a raised bed, especially if the soil is not well-drained to avoid Phytophthora root rot. Excessive rainfall and puddled water after irrigation create favorable conditions for root rot. While no raspberry cultivar is immune to Phytophthora, Latham, Boyne, Killarney, Anne, and Nordic are among the least susceptible cultivars, whereas, Titan, Heritage, and Reveille are susceptible to this disease. Blackberries and black raspberries are generally less susceptible to root rot than red or purple raspberries. Recommendations for chemical control of Phytophthora can be found in the 2016 Midwest Small Fruit and Grape Spray Guide available from University Extension.
REVISED: January 27, 2016