Lack of Foliage on a Lilac

Lilac Blight

• Lilac blight typically occurs in the spring and is caused by bacteria. Wet conditions, temperature fluctuations and poor air circulation act as multiplying factors for the bacteria. Overcrowded plants or those growing in shaded locations are especially susceptible. New leaves develop brown blotching, then wilt and turn black. Defoliation occurs and new growth is green but unhealthy. Attempts to alleviate the problem by pruning during cold, wet weather are futile. When warmer temperatures arrive, prune lilacs deeply, cutting stems well below the affected area. After cutting away all blackened and dead areas, clean around the lilac by raking and burning the cut branches. To keep lilac blight from spreading to healthy bushes, disinfect pruning shears with 3 parts rubbing alcohol to 1 part water or 1 part bleach to 3 parts water. Properly pruned lilacs have a reduced chance of developing this type of blight. Stimulate new growth by using a 10-10-10 liquid fertilizer.

Leafminers

• Lilacs that have been invaded by leafminers develop large, blotchy brown areas that can result in defoliation. The green leafminer larvae mine the leaves and roll them toward the leaf tips. Adult leafminers are small brown moths that feed on the leaves. Fallen leaves should be raked up and destroyed to decrease the pest population. In instances of severe defoliation, it may be necessary to use a chemical to get rid of leafminers. Spray as soon as the brown blotches are noticed.

Verticillium Wilt

• Verticillium wilt causes lilacs to wilt and drop leaves. It may affect only one branch or the entire tree. This disease is a soil-borne fungus that feeds off of lilac tissue. It survives in the soil by living on dead plant matter and penetrates the roots of the plant. It then releases spores that spread through the wood, infecting the plant. Misdiagnosis is common, and symptoms range from wilting and curling leaves to plant death. The first step to treating this problem is to clean up the soil conditions. Consult an arborist regarding ongoing problems.

Powdery Mildew

• Most lilac species are susceptible to powdery mildew infections, which typically crop up in mid-summer. Felt-like gray or white patches appear on the leaves and eventually cover the entire leaf. If the lilac is heavily infected, leaf drop may occur, but this fungus does little to affect the health of the plant. The main problem caused by the fungus is the loss of ornamental value. Conditions that encourage growth of the fungus include low nighttime humidity levels, high daytime humidity levels, temperatures ranging between 70 and 80 degrees Fahrenheit, irrigation and over-fertilizing. Plants grown in shady areas or those with poor air circulation are at increased risk of developing powdery mildew. Plants should be sprayed with a fungicide when symptoms are noticed, then spayed weekly to bi-weekly through the growing season.