Walnut trees are constantly under siege from several insects and diseases. My first season of growing walnuts ended when walnut husk flies destroyed nearly 40% of my crop. The larvae of these flies, which penetrate the developing nuts, produce distinctive black stains. Careful vigilance and timely treatment of the problem are the determining factors between a successful walnut orchard and a failed effort.
Walnut Husk Flies
- Identification: Yellow-striped adults emerge mid-July
- Damage: Maggot-filled husks, blackened shells
- Treatment: Apply spinosad every 10 days during egg-laying
Codling Moths
- Identification: Gray moths with copper wingtips
- Damage: Worm-filled kernels, premature nut drop
- Treatment: Install pheromone traps before bloom
Aphid Colonies
- Identification: Clusters under leaves with honeydew
- Damage: Curled foliage, sooty mold growth
- Treatment: Spray neem oil at dusk weekly
Root rot fungi thrive in soils that are waterlogged. I have lost three saplings in my clay-heavy plot before I put in French drains to improve drainage. Now I check for drainage by digging the holes 18 inches deep; if there is still water after 24 hours, I add gypsum along with coarse sand.
Preventative care is better than reactive care. I start using kaolin clay in June before the husk flies emerge. It reduces the number of egg-laying sites by 70% with a mineral barrier. I also plant companion tansy that repels moths while attracting parasitic wasps to attack moth larvae.
Read the full article: How to Grow Walnuts: 7 Essential Steps for Healthy Trees
