Answer: Blackberry plants are susceptible to a fungal rust. Infected leaves have small purple-red spots on the upper surface; while the underside will have yellow-to-creamy-white pustules. If this is what you are seeing, the best control is to prune away the infected leaves and remove them from your garden. If entire leaves are turning a rust color, rather than exhibiting rusty spots, it means the leaf has died. Water stress can cause this. Again, prune to remove the affected leaves. Blackberry bushes are vigorous growers and usually overcome these problems. I hope yours does, too.
Q&A Library Searching Tips