Grape leaf skeletonizier (Harrisina americana) larvae on wild grape leaves. Photo: HJB
Grape leaf skeletonizer (GSL) larvae have begun appearing in large numbers on grape vines in the last 2 weeks. I have received a few phone calls and emails about these insects. The distinctive yellow and black caterpillars are gregarious and a group of them feeding close together can quickly skeletonize a leaf. From a distance, leaves will appear light brown or gray. Larvae will be clearly visible as will their feeding.
GLS rarely cause significant damage in commercial vineyards because they are often controlled by insecticides applied for other insects. In homeowner plantings, they may reach damaging densities, but can be managed relatively easily (Bt is a good, effective choice, see a note about pesticide recommendations and hand removal may also be sufficient when the larvae are small and concentrated in a small area).