How to Manage Pests

Pests in Gardens and Landscapes

Gall makers

Most galls are caused by cynipid wasps and gall midge flies. The adult gall wasp is a small, stout, shiny insect with very few wing veins and a purple or black body. Adult gall midges are tiny, delicate flies, often with long, slender antennae. Some galls may be caused by gall mites or larvae of some moths.

Life cycle

Damage

Galls are distorted, sometimes colorful swellings in plant tissue caused by the secretions of certain plant-feeding insects and mites. These unusual growths may be found on leaves, flowers, twigs, or branches. Five species that are common are the honeylocust pod gall midge, the ceanothus gall moth, the baccharis gall fly, the twohorned oak gall wasp, and the willow leaf gall sawfly. Another species, the alder gall midge, Dasineura sp., can cause cupped leaves, thickened or galled along the midvein, because of a tiny pale larva feeding within tissue.

Solutions

Most galls are not known to harm trees. Prune and dispose of galls if they are annoying. This may provide control of some species if pruning is done when the immatures are in plant tissue and before the adults begin to emerge.

Galls on underside of valley oak leaves
PhotoName
Pink-spined turban galls (left) Redish oak cone galls (right)
Oak stem gall
Oak stem gall
Mossy rose gall Mossy rose gall

 

 


Statewide IPM Program, Agriculture and Natural Resources, University of California
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