Galls are formed from insect/mite feeding or egg laying activity. Mechanical damage or salivary secretions cause increased production of normal plant growth resulting in hypertrophy and hyperplasia. Galls form during growth periods, so usually late spring. Most galls do not adversely affect plant health. Chemical application requires precise timing. The spray must be applied during initial mite/insect activity before the gall forms. Once the gall forms the insect/mites are protected from sprays. Mainly galls are just an unsightly nuisance.