The following is a brief description of nematode species found in Washington vineyards. In general, nematodes weaken the root system, can cause secondary infections due to their feeding on the vine roots, and some species can infect vines with viruses, explains Dr. Ekaterini Riga, Washington State University nematologist.
Dagger—Of the two major dagger species found in grapes (Xiphinema pachtaicum and X. americanum), fortunately for Washington growers, the species associated with spreading virus (X. americanum) was not the prevalent species found in the state. Dagger nematodes are some of the largest nematodes and have a huge stylet (piercing mouthpiece) that can penetrate completely through the vine root, probing the same spot repeatedly. Daggers live outside the root and don’t like hot temperatures and dry environments; therefore, sampling should be done in the spring or fall, collecting soil near the roots. Young vines are easily damaged by the dagger’s root feeding. Roots that look like a witch’s broom, with the root tip damaged, indicate dagger nematodes.
Root knot—Grapevines that look small, perhaps chlorotic, could be infected with root-knot nematode. Symptoms are often mistaken for other vine maladies, such as phylloxera, poor plant nutrition, or poor irrigation. Affected grape plants are usually found in pockets in the field, making sampling difficult. The root-knot female enters the root and lives permanently inside the root, laying her eggs and deforming the roots. In observing roots that have been dug up, there will be knots or nodes, which are the eggs inside the root, and few root hairs. Root knot spreads easily to new areas by planting infected plants, moving infested soil or infested farm equipment, and this species has even been found in irrigation water. Root knot can cause problems in vineyards if the sites were previously cropped with potatoes or alfalfa. The best time to sample is early to late fall.
Ring—Ring nematodes cause root pruning, with damage not as obvious as that caused by root knot or dagger. Ring nematodes are the easiest to identify because they have jagged skin with a ring-like structure. Though found only recently in Washington vineyards, they are a problem in some California vineyards. The best time to sample is at the end of the growing season.
Lesion—The lesion nematode is migratory, spending part of its life cycle inside the root and part in the soil. It is a small nematode, but produces many eggs, some of which are laid inside the root. The nematode causes cell damage and makes the root accessible to other fungi and bacteria. Lesion nematodes are often found in apples, cherries, ornamentals, potatoes, and grapes, though in Washington, it has been found only in grapes along with other nematodes. It is not clear how much damage the nematode does to grapes, because it has not been found alone. The best time to sample is early to late fall.