Walnut Aphid

Walnut aphids are small, dark insects that congregate on walnut leaflets, causing leaf yellowing and wilting due to sap feeding. Honeydew production promotes sooty mold growth and attracts ants. Infestations typically develop by midsummer on walnut trees in warmer regions, though western Washington occurrence is uncommon due to limited walnut cultivation.

For landscape walnuts, prune to improve air circulation and reduce aphid habitat. Spray insecticidal soap targeting leaf undersides when populations first appear. Encourage parasitoid wasps and predatory beetles by maintaining flowering plants nearby. Most western Washington walnut areas experience minimal aphid pressure.