Yellow or cane and leaf rust of blackberry
SCIENTIFIC NAME of causal agent: Kuehneola uredines
SYMPTOMS: Affected plants first exhibit small yellow spots, or pustules called uredinia, on shoots and the undersides of leaves. Mostly, the uredinia appear in summer and late fall, about the time of harvest or later. The pustules erupt to produce masses of yellow spores, which are responsible for spread of the pathogen. The image on the calendar depicts heavily infected leaves. Yellow rust pustules may also cause small splits of canes. Cane rust can be confused with the more aggressive orange rust, a different rust disease that affects thornless blackberry varieties. Yellow rust can cause some defoliation and reduction in fruit production due to lack of vigor in canes, but the orange rust is more devastating of the two diseases. Distinguishing these two diseases requires the assistance of a trained diagnostician (see Resources below).
Cane and leaf rust is most severe on trailing varieties of blackberries. The fungus survives through the winter on infected canes. Wet spring conditions favor disease development by enhancing spore production and spread from uredinia on the canes to leaves. Further spread occurs during summer from leaves to leaves and leaves to canes by means of spore production in the uredinia.
- Proper diagnosis is the first step in managing this disease.
- Any cultural methods that reduce spore dispersal will reduce infections,
- Remove diseased canes following harvest – both older heavily infected canes as well as newly infected younger canes.
- Yellow rust, unlike orange rust, can be controlled with the timely and proper application of fungicides such as lime sulfur, fixerd coppers or myclobutinal.
- When applying any pesticide, read and follow label specifications, warnings and recommendations.
Authored by Dr. David Appel, Professor & Extension Specialist