Destructive Root Rot Ailment Afflicting Raspberry Plants
Raspberries, particularly black raspberries, are susceptible to a disease known as Verticillium wilt. Red raspberries, on the other hand, seldom suffer severe losses. If raspberries are to be planted in an area where the disease has previously been a problem, it is generally recommended that they not be replanted.
Starting with disease-free plants is critical in preventing the initial contamination and spread of Verticillium wilt. Using disease-free nursery stock from fields known to be free of Verticillium is essential. If raspberries are replanted in an infested site, soil fumigation should be considered.
Soil fumigation can be an effective control strategy for Verticillium wilt. Soil fumigants such as TELONE™ (1,3-dichloropropene) combined with Chloropicrin have been applied successfully in raspberry production areas like Coastal California to control soil-borne fungi including Verticillium, nematodes, and other pathogens. However, reintroduction of the pathogen into fumigated soils is a major concern with using soil fumigation.
Crop rotation is another recommended method for reducing Verticillium inoculum in soil. Rotating raspberries with non-host crops interrupts the pathogen lifecycle and reduces soil infestation levels. Avoiding susceptible crops such as potatoes or tomatoes in rotation can help diminish inoculum density. However, the effectiveness of rotations with nonsusceptible crops may vary between different geographical locations.
Fungicides generally have limited efficacy against Verticillium wilt because it is a soil-borne vascular pathogen. While fungicides may help manage some foliar diseases or saprophytic fungi, fungicidal control of Verticillium in raspberries is less well-supported and not highlighted as a primary strategy. Instead, an integrated management approach focusing on starting with disease-free plants, applying soil fumigation before planting, and practicing effective crop rotations represents the most effective approach for controlling Verticillium wilt in raspberries.
Symptoms of Verticillium wilt on raspberry plants often appear in June or July for black raspberries, and a month later for red raspberries. The lower leaves of diseased plants may have a dull green cast, wilt, turn yellow, and drop. Infected raspberry canes may die before fruit matures, resulting in withered, small, and tasteless fruit.
Verticillium wilt is usually a cool-weather disease, most severe in poorly drained soils and following cold, wet springs. The fungus, Verticillium alboatrum, can survive in the soil for many years. It can penetrate roots directly or through breaks or wounds, and grows into the water-conducting tissue (xylem), causing the plant to die.
This fact sheet was originally published in 2008. While the information provided remains relevant, it is always advisable to consult with local extension services or agricultural experts for the most current and location-specific advice on managing Verticillium wilt in raspberries.
Scientists recommend using disease-free nursery stock from pathogen-free fields to prevent the initial contamination and spread of Verticillium wilt in raspberries. To reduce the inoculum of Verticillium, crop rotation with non-host crops can interrupt the pathogen lifecycle and minimize soil infestation levels.
