PestLow Severity

Oak Gall Wasp

Amphibolips confluens (and 717 other species in North America)

Small cynipid wasps that create distinctive large, shiny, round galls on oak leaves through growth-regulating chemicals. While causing no apparent damage to trees, fallen galls can damage lawn mowing equipment. Part of a diverse complex of 717 gall wasp species attacking oaks in North America.

Peak Season: Egg laying: Late summerOverwintering: Larvae in gallsDevelopment: Two-year cycleAdult emergence: Second summer from mature gallsPeak gall formation: Following egg laying periods
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Oak gall wasp galls showing large, round formations on oak leaves and twigs

Identification & Symptoms

What to Look For

Large, shiny, round galls below leaf petiole or mid-rib
Some galls as large as apples
Galls contain spongy center with mass of fibers radiating from larval capsule
Thin, papery shell around gall when dry
Multiple galls may occur on single leaves
Fallen galls accumulating under trees

Potential Damage

No apparent damage to tree health or vigor
Aesthetic impact from numerous large galls
Fallen galls damaging to lawn mowing equipment
Potential minor reduction in photosynthetic leaf area
Generally considered a cosmetic rather than health issue

Lifecycle

Complex lifecycle not fully understood. Two-year cycle with two broods - one of only females and another of both sexes. Single larva per gall. Eggs hatch in late summer, larvae overwinter in young galls, and adults emerge from galls the second summer.

Professional Treatment Approach

1

Generally no treatment necessary due to lack of tree damage

2

Remove fallen galls before mowing to prevent equipment damage

3

Aesthetic pruning of heavily galled branches if desired

4

Focus on maintaining overall tree health

5

No chemical treatment typically recommended

Recommended Mauget Products

No chemical treatment typically needed

Professional-grade treatment specifically effective against oak gall wasp.

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