Grape cane girdler-An insect pest, the grape cane girdler (Ampeloglypter ater LeConte) can cause physical damage to shoots and petioles.
(Photo credits: left: Virginia Tech (Virginia Fruit Page), right: University of Kentucky)
Downy mildew-Severe downy mildew infection can cause defoliation. However, unlike Pierce’s Disease, both the leaf blade and petiole will be dropped.
(Photo credit: Mizuho Nita)