What's eating my japanese walnut?

Japanese walnut shares the Juglans family's key pests — walnut caterpillar can defoliate trees rapidly and walnut husk fly degrades the nut crop. Squirrels exploit the large, thin-husked nuts aggressively. Scale insects occasionally colonize bark on established trees. Pest pressure is generally lower than for black walnut in North American plantings.

Large communal colonies of hairy caterpillars strip branch after branch; repeated defoliation weakens the tree and can cause dieback in young specimens. Scout in July–August; hand-remove colonies and apply Bt kurstaki when caterpillars are under 1 inch; avoid spraying when beneficial insects are active.

Larvae feeding inside husks produce dark, wet rot; affected kernels are bitter or shriveled at harvest. Begin kaolin clay applications by mid-July; follow with spinosad at label rates; remove and destroy all fallen nuts promptly.

Nuts are removed from the tree before full maturity; even a small squirrel population can take 80–100% of the crop on a young tree. Fit trunks with smooth metal collars; use live traps; harvest as soon as husks show the first signs of loosening.