Galls form during the rapid growth of new leaves, shoots, and flowers in late spring. Insects or mites chew on the plants, and their saliva causes the plants to produce more growth hormones, leading to galls. These growths continue even after the insects die and often stay on plants for more than one season.
Types of Galls:
1. Leaf Galls:
- Form on leaf blades or petioles.
- Most common type.
- Appear as curls, blisters, nipples, or hairy growths.
- Found on upper or lower leaf surfaces.
2. Stem and Twig Galls:
- Deform stems and twigs.
- Range from slight swelling to large knots.
3. Bud or Flower Galls:
- Deform the size and shape of buds and flowers.
Damage Caused by Galls:
- Galls need nutrients just like other plant parts.
- They can steal vital nutrients, affecting plant growth, especially in young plants.
- Severe damage can occur if many galls are present for several years.
- Usually, galls are not numerous enough to harm the plant.
Protecting Your Plants:
- Most galls do not cause severe damage, so control is often unnecessary.
- Chemical treatments are tricky since timing is crucial.
- Apply pesticides before gall formation begins but when insects and mites are active.
- Once galls form, it's too late for treatment.
- For pests that overwinter on plants, use horticultural oil before spring insect activity.
Author: Robin Trott, Extension educator, Douglas County