What Causes My Blackberries to Get Hard White Spots on Them?

Cause

• Hard, white bumps on the blackberry are an indication of the presence of an insect called rose scale (Diapsis rosae). It is a common pest on brambles and is especially attracted to blackberries. These tiny insects are circular or elliptical and about 1/8 inch in diameter. A large infestation can cause the blackberry's canes to appear white and reduce the plant's vigor. The white scale's eggs hatch in late spring or early summer, and a second hatching occurs in late summer.

Solution

• Remove infested canes. Don't compost the removed material; it's best to burn it, if possible. Otherwise, bag it and remove it from the garden. Scout out areas around your property where wild brambles may be growing and prune those as well. Adult scales have a waxy, hard armor that is resistant to most insecticides. The larvae, known as "crawlers," may be controlled with horticultural oil sprays. Timing of the application is critical. Wrap double-sided tape around the canes to help monitor crawler activity in June and again in August. As soon as they become evident, apply horticultural oil according to label instructions.

Prevention

• Prevent white scale by spraying the brambles with lime sulfur during the dormant season, according to label instructions. This helps kill scales overwintering on the canes. Lime sulfur must be applied when temperatures are above 50 degrees Fahrenheit, so don't wait too long after the plant goes dormant to make the application. Monitoring wild blackberry bushes in the vicinity and treating those helps cut down the likelihood of an infestation.

Considerations

• Scale insects have natural enemies, such as certain wasp species and ladybugs. Releasing ladybugs during the growing season may help control a small infestation. Purchase ladybugs at large gardening centers and nurseries. Avoid the use of insecticides, if at all possible, to keep from killing the pest's predators and the blackberry's pollinators. If you find you must use an insecticide, check the label to ensure the product is safe to use on blackberry bushes.