Red Spikes on Willow Trunk? It’s Borer Frass—Here’s What to Do

Those rubbery, red spikes covering your young willow’s trunk are not a fungus—they’re frass (insect excrement) from borers, likely beetles, that have infested the wood. Heavy frass accumulation up the entire trunk indicates a severe infestation.

Treatment Options

Spray the trunk thoroughly with an insecticide labeled for borers, such as Merit (imidacloprid) or Onyx (bifenthrin). However, with this level of infestation on a three-year-old tree, the chance of survival is low.

Address the Underlying Stress

Borers target stressed trees. After treatment, fertilize with 1 lb of 10-10-10 fertilizer per inch of trunk diameter, scattered around the drip line and watered in well. This helps the tree recover vigor and resist future attacks.

Monitor and Decide

If the tree continues to decline, removal may be necessary to prevent borers from spreading to nearby trees.