I live out on the north side of a small mountain in the Ferndale area. I try to grow things on our ten acres, with modest success. I set out blackberries a couple of years ago, beside a small running creek, but not below water level. This summer, they developed some black spots and a couple of vines passed on, the remainder did produce a couple of quarts. I am thinking they had some kind of a rust perhaps, because I do have oaks and cedars in our area. Should I be applying some type of dust such as rotenone?
There are several things that could be impacting your blackberries, but from the sound of it, it isn’t insects, so rotenone would not be affective. I also don’t like dusts. If you are going to spray, we need to properly identify the disease (with leaf samples next year) and then find the appropriate fungicide. There is one disease called double blossom (or rosette) that affects blackberries that is not curable. It is common when we have wild blackberries nearby that can spread the disease. It causes excessive thorniness on the stems and deformed almost double blossoms—thus the common name. It can kill plants, but usually in a slow manner. Pruning out infected canes helps. There is a rust disease that affects blackberries that is controllable. It produces very bright orange spores that can be rubbed off. Cedar apple rust does not affect blackberries, but does affect apples. There are other leaf spotting diseases as well as stink bug damage to the fruits. If you have the problems again next growing season, bring in a sample or take a picture and send it in so we can properly identify the problem before recommending a control.
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