Remove and destroy fallen leaves. Plant in a sunny area, do not crowd plants, and avoid overhead watering. Chemical applications should begin before new foliage is infected. Thiophanate-methyl or a sulfur fungicide may be applied. Read and follow all directions on the label.
Crown gall is caused by the soil-inhabiting bacterium Agrobacterium tumefaciens .
Large, corky galls up to several inches in diameter appear at the base of the plant and on the stems and roots. The galls are rounded, with a rough, irregular surface. Plants with numerous galls are weak, growth is slowed and leaves turn yellow. Branches may die back. The galls disrupt the flow of water and nutrients to the top of the plant.