These symptoms are easier to see when the leaf is placed in front of a bright light. Foliar nematodes are easily extracted from infested tissue by cutting the plant material into small 5 cm squares and incubating them in water. In just a few minutes hundreds of microscopic nematodes migrate out of the tissue and start swimming the water with rapid undulating movements. They can be seen with a dissecting microscope. The population of nematodes is usually severely reduced in the winter and gradually increases throughout the growing season, so that infected plants do not show any symptoms in the early spring.
Symptoms start appearing in the early summer and increase as the season progresses.
Foliar nematodes rarely kill their host, but they reduce the plant's vigor and the symptoms are unsightly. Vegetatively propagated plants can be a noxious source for spreading this nematode over large distances. As some plants are symptomless carriers, and symptoms in other plants are not apparent until populations are very high, spread of this nematode is a threat whenever new plants are introduced into the landscape or garden. The nematodes are likely to spread by water splashing them from infected new transplants to other suitable plants. In the fall when the leaves drop, the nematodes dry up in the plant tissue and become dormant.