Sawdust and Sticky Droplets Under Mimosa: Borer and Aphid Combo

Fine sawdust on your car plus sticky droplets attracting flies under a mimosa tree signals two simultaneous insect issues: wood borers and honeydew-producing insects.

Decoding the Evidence

Sawdust (frass): Indicates borer larvae tunneling in branches or trunk. Common mimosa borers include carpenterworms and clearwing moths. The frass falls from exit holes you may not see from the ground.

Sticky droplets: Honeydew from aphids, soft scales, or whiteflies feeding higher in the canopy. The sweet liquid attracts flies, ants, and bees.

Why Now?

Mature trees (12+ years) become more susceptible to borers as vigor declines. The combination suggests the tree is stressed—possibly from age, drought, or root issues.

Action Plan

1. Hire an arborist to inspect upper canopy for borer holes, dieback, and aphid colonies
2. Systemic imidacloprid soil drench controls both aphids and some borers
3. Trunk spray for borers (permethrin/bifenthrin) timed to adult emergence
4. Improve tree vigor: deep watering, mulch, soil-test-based fertilization

Mimosa is relatively short-lived (15-20 years). At 12 years with borers, evaluate whether investment in treatment makes sense versus planning replacement.