What's eating my butternut?

Butternut (white walnut) faces serious threats from walnut caterpillar, which can defoliate trees, and walnut husk fly, which ruins the edible crop. Squirrels are relentless nut thieves. The species is also severely afflicted by butternut canker disease (Ophiognomonia clavigignenti-juglandacearum), making vigor-maintenance pest control doubly important.

Colonies of dark, hairy caterpillars strip entire branches bare in late summer; frass and shed skins accumulate on bark below. Hand-remove egg masses and early-instar colonies; apply Bacillus thuringiensis (Bt) when caterpillars are small; band trunks with sticky barriers to intercept larvae descending to pupate.

Maggots tunnel through the green husk, causing blackened, rotting husks that stain and shrink the kernel; shells may not open cleanly. Apply kaolin clay or spinosad-based sprays from mid-July through hull split; harvest promptly and destroy infested husks; remove dropped nuts to break the cycle.

Nuts are harvested weeks before maturity and buried; a heavy squirrel population can take virtually the entire crop. Install metal banding (18–24 in) around trunks; use cage traps to reduce local population; harvest nuts as soon as husks begin to loosen.

Silken webs enclose branch tips; caterpillars feed within the web, browning foliage and weakening stressed trees. Prune and destroy webs while small; apply Bt or spinosad to break through webbing; encourage parasitic wasps by avoiding broad-spectrum insecticides.