Why Is My Winterberry Losing Black Leaves?

Winterberries (Ilex verticillata) are deciduous shrubs that bloom in the spring and produce an abundance of berries that ripen to showy red in late summer and fall. They are hardy in U.S. Department of Agriculture plant hardiness zones 3 to 9. While not highly susceptible to diseases and insect attacks, there is one disease and one type of insect that can cause winterberry leaves to turn black and drop from the shrub.

Messy Insect

Soft scales are small, round or oval insects that are less than 1/4-inch long. They can look cottony, smooth or waxy, depending on the type of scale. These insects puncture the winterberry leaves and feed on the plant juices. The leaves may turn yellow, wilt and fall from the shrub and the entire shrub may become less vigorous but soft scales rarely do serious harm. In addition to feeding on the shrub, soft scales secrete a clear, sticky substance called honeydew. Sooty mold grows in the honeydew, which can turn the leaves black, blocks the sunlight and causes them to drop from the shrub.

Eliminate the Insects and the Mess

Branches that are heavily infested with scale insects should be pruned off. The winterberry shrub can be treated with horticultural oil to kill the remaining scale insects. It is commonly diluted with water at a rate of 2 percent. Pour the mixture into a spray bottle and spray the winterberry thoroughly, paying close attention to the undersides of the leaves and branches. The scales must be coated with the oil. Do not spray the shrub when temperatures are expected to be above 90 degrees Fahrenheit or below 32 degrees or when rain or fog is expected within 24 hours. After the scale insects are under control, the sooty mold and honeydew can be washed off the leaves with a mixture of 1 teaspoon of mild dish soap per gallon of water. Rinse the soapy water off right away.

Spreading Spots

Leaf spot diseases can cause the leaves of a winterberry shrub to turn black and drop. They can be caused by fungi or bacteria. While they commonly start out as clearly defined spots on the leaves, eventually the spots will grow until the entire leaf is black or brown. These diseases commonly occur when the weather is wet.

Spot Removal

Winterberry shrubs usually tolerate leaf spot disease with minimal damage. The infected and dead branches should be pruned off. Dip the hand pruners in household disinfectant and wipe them off with a clean cloth between cuts to avoid spreading the disease to healthy branches. Rake up any fallen leaves or debris around the shrub and place it and the pruned branches in the trash. Water the shrub from below the branches to keep the foliage as dry as possible. Give the shrub 5 to 10 gallons of water once or twice per week when it does not rain. Winterberry shrubs grow best and will recover more quickly in soil that stays uniformly moist.

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