What's eating my black walnut?

Black Walnut (Juglans nigra) is attacked by walnut caterpillar, walnut aphid, walnut husk fly, fall webworm, and squirrels. It is generally more pest-tolerant than English Walnut but squirrels are relentless; walnut caterpillar can defoliate entire trees in late summer. Squirrels remain the top practical threat at harvest.

Gregarious caterpillars skeletonise leaflets in colonies, then strip entire branches; mature larvae move to bark to pupate, leaving rings of frass; repeated defoliation weakens trees Knock clusters of young caterpillars into a bucket of soapy water; apply Bt (Bacillus thuringiensis) spray when caterpillars are small; scrape pupation rings from bark

Dense colonies on leaflet undersides from spring; honeydew drips onto surfaces below; heavy infestations cause early defoliation Natural predators (parasitic wasps, lacewings) usually control populations; spray with insecticidal soap for severe outbreaks; avoid broad-spectrum pesticides

Silken webbing enclosing branch tips from late summer; caterpillars feed within the web, defoliating enclosed foliage Prune out and destroy web tents while caterpillars are still small; apply Bt or spinosad spray to break open tents and contact larvae; damage is mainly cosmetic on established trees

Strip the entire nut crop before maturity; chew through hull to reach kernel; may gnaw bark on scaffold branches Baffled trunk guards; harvest nuts as soon as hulls begin to crack; netting the canopy of smaller trees; repeated removal of individuals in high-pressure gardens