Woolly Aphids on Elm Trees: Identification and Control

Central Virginia elms are covered in white, cottony insects with sooty droppings underneath. Bees, yellowjackets, and butterflies swarm the trees. The homeowner asks if these are woolly aphids and whether treatment is needed.

Yes, They're Woolly Aphids

Woolly aphids are sap-feeding insects that secrete waxy filaments, giving a cottony appearance. They excrete honeydew—a sugary liquid that coats leaves and ground, fostering black sooty mold and attracting stinging insects.

Damage Potential

• Heavy infestations can distort leaves and stunt shoots.
• Sooty mold blocks photosynthesis but doesn't invade tissue.
• Honeydew creates a nuisance on surfaces below.

Control Options

Contact Insecticides (spray foliage)

Acephate (Orthene), bifenthrin (Talstar), malathion, pyrethrum, and others. Thorough coverage is essential; aphids hide under wax.

Systemic Insecticides (soil or trunk application)

Imidacloprid (Bayer Advanced Tree & Shrub Insect Control) applied as a soil drench provides months of control with less impact on beneficials. Acephate can also be used systemically.

Cultural Notes

• Spraying large elms is difficult; soil-applied systemics are often more practical.
• Check local nursery for registered products and follow label directions.
• Natural enemies (lady beetles, lacewings) often suppress aphids eventually.

Treatment isn't always necessary—many trees tolerate aphids with only cosmetic effects. Decide based on nuisance level and tree value.