Most Common Black Walnut Tree Pests:
Identification and Treatment Guide

Black walnut trees are prized for their beautiful wood and delicious nuts, but they are also vulnerable to a variety of pests that can threaten their health and longevity. In order to protect your black walnut trees, it is important to be able to identify the most common pests and understand how to effectively treat them. This guide will introduce you to some of the most prevalent pests that target black walnut trees and provide guidance on how to manage infestations.

Walnut Caterpillars

Walnut caterpillars are a common pest that can defoliate black walnut trees if left unchecked. These caterpillars are easily identified by their black bodies with yellow stripes and rows of spines along their backs. They typically feed on the leaves of the tree, causing significant damage if their populations are allowed to grow unchecked.

Treatment:

• Manual Removal: Handpick caterpillars from the tree and drop them into a bucket of soapy water to kill them.
• Biological Control: Introduce natural predators like parasitic wasps or birds that feed on caterpillars.
• Chemical Control: Use insecticides specifically labeled for caterpillar control, following all safety precautions and application instructions.

Walnut Twig Beetles

Walnut twig beetles are small insects that bore into the twigs and branches of black walnut trees, causing dieback and ultimately tree mortality. These beetles are carriers of the fungal pathogen that causes thousand cankers disease, which is a serious threat to black walnut populations in certain regions.

Identification:

• Look for tiny holes in the twigs where beetles have entered.
• Pay attention to wilting or yellowing leaves, which may indicate twig beetle damage.

Treatment:

• Prune Infested Branches: Remove and destroy affected branches to prevent further spread.
• Insecticidal Treatments: Apply systemic insecticides early in the season to protect trees from beetle infestations.
• Preventative Measures: Keep trees healthy with proper watering and fertilization practices to reduce susceptibility to beetle attacks.

Walnut Lace Bugs

Walnut lace bugs are small insects that feed on the undersides of black walnut leaves, causing stippling and discoloration. Heavy infestations can weaken the tree and impact its overall health.

Identification:

• Look for tiny, flat insects with lacy wings on the undersides of leaves.
• Check for yellow or brown stippling on the upper leaf surface.

Treatment:

• Horticultural Oils: Apply horticultural oil to suffocate lace bugs and their eggs.
• Insecticidal Soaps: Use insecticidal soaps to control lace bug populations without harming beneficial insects.
• Regular Monitoring: Inspect trees regularly for signs of lace bug activity and treat early to prevent widespread damage.

Walnut Husk Flies

Walnut husk flies are another common pest of black walnut trees, targeting the developing nuts within the husks. Infestations can lead to reduced nut quality and yield, impacting both commercial orchards and backyard walnut trees.

Identification:

• Look for small maggots inside developing walnuts.
• Monitor for early signs of husk discoloration or premature nut drop.

Treatment:

• Sanitation Practices: Remove fallen nuts and husks promptly to reduce breeding sites for flies.
• Trapping: Set up pheromone traps to monitor fly populations and reduce mating success.
• Chemical Control: Apply insecticides at key developmental stages of the nuts to prevent fly infestations.

By familiarizing yourself with these common pests of black walnut trees and implementing appropriate management strategies, you can help protect your trees from serious damage and ensure their continued health and productivity. Regular monitoring, early intervention, and a combination of cultural, biological, and chemical control methods will help keep your black walnut trees thriving for years to come.