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Blackberry Plant Diseases

By Carole Ellis ; Updated September 21, 2017
Keep your blackberry plants disease-free.
Blackberry image by Evgeniya Samburceva from Fotolia.com

Blackberry plant diseases can destroy plants and crops in no time flat. It can be incredibly frustrating to pour time, love and energy into blackberry bushes, only to discover that that the fruits are dry, corky, sour or non-existent thanks to undetected diseases. Keeping an eye on your fruit plants will help to ensure expected yield at the end of the summer.

Blackberry Rusts

Blackberry rusts are a form of fungal infection. They are orange or brown in color and coat the lower surfaces of the leaves with raised, discolored blisters. The rust will not kill the plant but will reduce blooming and fruit set as well as being systemic and eventually overrunning the plant. Prevent blackberry rusts by eradicating all wild blackberry plants near your plant stock and by removing any infected plants as soon as symptoms appear. Keeping weeds down can help prevent the spores of the rust from germinating. Lime sulfur is an effective control for this fungus.

Mold and Powdery Mildew

Mold and powdery mildew are prevalent problems where blackberry plants grow in humid environments. These infections appear as black, gray or white growths on the leaves, stems and fruit. Neither will kill the plant right away. If you already have infected flowers and fruit, avoid treating the plants with fungicide until after harvest. Prune away affected areas and discard the debris. Do not leave it on the ground. Water with a drip hose in the morning. Avoid watering in the afternoon and evening. Powdery mildew responds well to copper fungicides and Bordeaux mixture.

Cane Diseases

Cane diseases in blackberry plants impact the canes or stems. Phytophthora, botrytis and cane blight all create spots and discolorations that can be brown, black, purple or olive colored. You may spot lesions or cankers on the canes. In the spring, when the plants are first starting to grow, prune back dead and diseased canes to make more room for the healthy canes. Make sure plants are far enough apart that they will dry quickly after irrigation. Remove affected parts of the plants as soon as you spot them to prevent spread. Some types of cane diseases can be managed with lime sulfur treatments. Consult a professional before starting treatment to make sure you have the proper diagnosis and that these treatments are safe for your garden area.