Red Ringspot Disease
The cause of red ringspot virus is unknown. Mealybugs, however, may be involved in transmitting this virus. Infected stems at least 1 year old often exhibit reddish- brown spots with green centers. The spots, 1/8 to 1/4 inch in diameter, also develop on the upper surfaces of older leaves in mid- to late summer. The powdery mildew fungus can cause similar symptoms on both sides of the leaf. Plants with this disease exhibit a loss of crop; the amount varies with variety. Because the vector has not yet been identified, the primary form of control is the use of virus-free stock and removal of infected bushes. Blueray and Bluetta are especially susceptible.