Larvae: After a few days, the eggs hatch and small larvae begin eating the inner leaf tissue. As they eat, the leaf forms red bumps or galls. Larvae have dark heads, pale bodies and are about 5 mm long. Larvae have true legs present on their thorax and prolegs on each abdominal segment.
Pupae: In mid-summer, larvae leave the leaf gall and drop to the ground to pupate. A second brood pupates in the fall and over winters in this stage.
Adults: In late spring, adults emerge to reproduce. Adults appear like long, shiny, black wasps and are quite small (3.5 to 5 mm long.)
Bumps projected on both sides of willow leaves: As larvae eat, they create a bean-shaped, smooth bumps on both sides of willow leaves called a gall. Galls may green, yellow, or red in colour. The galls are only cosmetic and do little or no harm.
Follow a regular watering, fertilizing, and pruning schedule to keep your trees as healthy as possible to resist attack.
Avoid planting willow trees which are their preferred food sources.
Rake up and destroy leaf litter in the fall where willow redgall sawflies pupate.
Pick off infected leaves to improve cosmetic appearance of tree.
Biological tools: Not applicable
Least toxic chemical tools:
Regularly apply insecticidal soap on infested leaves. Follow directions on the label.