Cynipid Gall Wasps

Pest Description

• adults: very tiny and seldom seen
• larvae: grub-like; found within galls
• pest noticed by the presence of galls
• each species creates a unique gall

Host Plants, Diet & Damage

• most common on roses and oaks
• galls can occur on acorns, branches, buds, flowers, leaves, roots and twigs
• larval feeding causes round, spiny, single/multiple or other types of galls
• galls do not typically affect the overall health of the tree
• excessive galling of branches and twigs can cause plant stunting or dieback

Biology, Life Cycle & Damaging Life Stage

• overwinter as larvae in the gall
• pupate within the gall or in the soil in spring
• emerge in April and May, coincident with budbreak
• eggs laid on emerging plant tissue or on/in swollen buds
• larval feeding produces galls
• most have one generation per year
• larvae are the damaging stage

IPM Recommendations

• Galls do not affect the overall health of the tree; tolerate pest.
• Rake and remove fallen leaves in the fall.
• Remove galled plant parts and destroy.
• Management with insecticides can be difficult and spotty.
• Apply an insecticide (carbamate; pyrethroid) at or just prior to budbreak to prevent egg laying to reduce gall formation (may not prevent all new gall formation).