Galls are abnormal outgrowths, often caused by insect parasites, fungal infections, or bacterial infections, which can develop in a tree’s leaves, roots or branches. They can vary greatly in size, from tiny bumps on a leaf to massive tumors growing out of a tree trunk.

Insects alone are responsible for hundreds of unique gall varieties. For them, these outgrowths serve the dual purpose of acting as a source of food as well as a habitat. Insect galls are created as a direct result either of eggs being laid in the area or due to feeding on the part of the gallmaker.

One of the most prevalent varieties of fungal or bacterial related galls is crown gall, which affects over 600 species of plants.

Caused by the bacteria “Agrobacterium tumefaciens,” it primarily enters through wound points and tends to have the greatest negative effect on trees between one and eight years old.

To eliminate insect galls, preventative measures can be effective, although the timing for applying insecticides must be precise in order for it to be a viable option. Contact insecticides can also be used to kill gallmaker insects that have reached the adult stage.

For fungal gall infections, spraying a fungicide can work to prevent growth the following year, while in the case of bacterial galls like the crown variety, a combination of bactericide, surgery, and flaming can help remove the tumorous growths. Crown gall cases can also be managed by introducing a greater number of non-infected trees to the area.