Bacterial Blight of Lilac

Bacterial blight of lilac is caused by the bacterium Pseudomonas syringae. Infection results in brown spots on leaves and internodes. These spots may enlarge and coalesce, causing leaves to become misshaped. Eventually leaves may be killed. When the infection spreads around a twig, it becomes girdled and dies. This phase of the disease is evident as new shoots develop in the spring. The shoots turn a black color, droop over, and die.

Control consists of pruning out blighted twigs as soon as they occur. Pruners should be dipped in bleach or 70% alcohol between cuts to prevent spreading the disease. Cut several inches below the margin between healthy and diseased tissue. Prune in dry weather only. As a preventative measure, thin plants to provide good air circulation. You may spray a copper- based product, such as Bordeaux mixture, 2 to 3 times at intervals of 7 to 10 days, starting when new growth appears in the spring.

This article originally appeared in the May 19, 1995 issue, p. 72.

Issue: 
Category: 
Authors: 

Links to this article are strongly encouraged, and this article may be republished without further permission if published as written and if credit is given to the author, Horticulture and Home Pest News, and Iowa State University Extension and Outreach. If this article is to be used in any other manner, permission from the author is required. This article was originally published on May 19, 1995. The information contained within may not be the most current and accurate depending on when it is accessed.