What's eating my heartnut?

Heartnut (the heart-shaped Japanese walnut variety) is targeted by walnut husk fly, which ruins the distinctive flat kernels, and walnut caterpillar, which defoliates rapidly. Because husks are thinner than black walnut, husk fly damage shows earlier and is more economically significant. Squirrels exploit the exposed nuts readily; deer browse young shoots in winter.

Maggots tunnel through thin husks, producing black slime that penetrates to the shell and ruins the pale, sweet kernel; shells may fuse shut. Apply kaolin clay from early July; follow with spinosad sprays at 7–10 day intervals until husk split; destroy all infested husks on or under the tree.

Colonies defoliate branch by branch through late summer, reducing photosynthate needed to fill kernels. Hand-pick early colonies; spray Bt when larvae are small and not yet clustered tightly; trim and bag infested branches.

The thin husk and heart shape make heartnuts easy for squirrels to handle; crop losses can be near-total on isolated trees. Install metal trunk guards 6 ft high; harvest at first husk loosening; cage individual clusters with bird netting during the final ripening weeks.