by azhadminKM

Two years ago, we decided to prune eight of our crape myrtles back to small tree status. They had not been taken care of for a decade and had grown 30 to 40 feet tall and were very gangly after so many years of neglect. After pruning, they flowered beautifully, but, about three weeks into flowering, we noticed what looked like white powder on the flowers and leaves. Unfortunately, zoo summer camp had started and it was another three weeks before I could inspect them to confirm that they had powdery mildew.

Once powdery mildew was confirmed, the next thing that was needed was to determine what we could use to treat the trees, since they are used for browse. Consulting the list of pesticides approved by our veterinarian, horticultural oil and Neem oil were our best options. I started with Neem oil, using the seven-day application schedule recommended on the package (once every seven days). Over the next four weeks, we were able to reduce the impact of the powdery mildew. Even though we continued with a 14-day application schedule, we were never able to completely eradicate powdery mildew that season. The powdery mildew has come back for the last two blooming seasons, but we have been able to knock it back to an acceptable level, with just a little white on the trees, by treating with Neem oil every seven days.

These crape myrtles appear to be Lagerstroemia indica, which are susceptible to this fungal disease. So that the pathogen is not spread to other plants, we clean the pruners after each use with a thymol solution, which kills most pathogens, including powdery mildew. Listerine “Original,” which has thymol as its active ingredient, is what I used; an inexpensive option.

submitted by Larry Hintz, Gardener, Sacramento Zoo