Controlling Scale Insects on Weeping Willow with Systemic Insecticide

Identifying the Pest

The "scales" covering your weeping willow leaves are almost certainly scale insects—small, immobile pests that attach to leaves and stems, sucking plant sap. They appear as tiny bumps (often brown, tan, or white) and can cause yellowing, premature leaf drop, and branch dieback if unchecked.

Effective Treatment: Systemic Insecticide

The most reliable control for scale on a large tree is a systemic insecticide applied as a soil drench. Products containing imidacloprid (e.g., Bayer Advanced Tree & Shrub Insect Control) are taken up by the roots and distributed throughout the canopy. When scales feed, they ingest the insecticide and die.

Application Steps

1. Measure the trunk diameter at 4.5 feet above ground.
2. Mix the product according to label rates (usually per inch of trunk diameter).
3. Pour the solution evenly around the base of the tree, within the drip line.
4. Water thoroughly after application to move the chemical into the root zone.

Timing and Expectations

• Apply in early spring as leaves emerge, or in fall.
• Control may take 2–4 weeks as the product translocates.
• One application typically protects for 12 months.
• Dead scales may remain attached; they will eventually weather off.

Additional Care

Keep the tree well-watered during dry periods to reduce stress. Avoid broad-spectrum foliar sprays that kill beneficial insects like lady beetles and parasitic wasps, which naturally suppress scale populations.