Rosette, or double blossom, is one of the most severe fungal diseases of blackberries grown in the southeastern United States. Many blackberry crops fall prey to the disease, which reduces yields and fruit quality. They also recommend making a fifth application immediately after harvest. In the past, farmers have been disappointed with fungicide treatments, because they thought spraying would control the disease in that year's crop. Benomyl is the most effective fungicide tested for controlling rosette, which is caused by the fungus Cercosporella rubi.
Few fungicides are registered and available for controlling blackberry diseases.
ARS researchers plan to evaluate some new fungicides for controlling rosette. Overcoming rosette would offer a high-value crop that costs less to establish than strawberries and blueberries. A natural protein called avidin, found in egg whites, is being developed into a new biopesticide in a partnership between ARS researchers and a Texas agricultural biotechnology company. The first scientific studies of the protein's lethal effect on stored-product insects were conducted by ARS researchers in the early 1990s. Avidin binds up biotin, an essential vitamin for insect growth, creating a vitamin deficiency that stunts the insects' growth or kills them.