Root Knot Root knot, or root gall, is caused by nematodes. Nematodes are tiny worms that feed on many kinds of plants. They are most damaging where winters are mild, where the growing season is warm, and where the soil is light. Nematode-infected plants lack vigor. They produce only a few small flowers.
Stems are short and thin.
Leaves are light green. Large roots become swollen and stubby. Small roots develop knobby outgrowths. QDig out and burn heavily infected plants. If possible, plant lawn grass on the infested soil and let it grow 2 years before you replant peonies.