Plant parasitic nematodes live in soil and plant tissues and feed on plants by puncturing and sucking the cell contents with a spearlike mouthpart called a stylet. Of the several genera of plant parasitic nematodes detected in California orchard soils, root knot, ring, lesion, and dagger nematode are considered to be the most important. Damage caused by nematodes may first become evident during the first year after planting. Feeding by root knot nematodes can impair root functions such as uptake of nutrients and water. Ring nematode infestation impairs development and function of peach roots and predisposes trees to bacterial canker.
Lesion nematodes penetrate roots and cause damage by feeding and migrating through the root tissues.
Dagger nematodes feed from outside the roots, but can reach the vascular tissues with their long stylet and are capable of reducing vigor and yield of trees. However, the main damage caused by the dagger nematode, X. americanum, is that it vectors a strain of tomato ringspot virus that causes peach yellow bud mosaic, which debilitates and can kill trees. The symptoms described below are indicative of a nematode problem, but are not diagnostic as they could result from other causes as well Symptoms of root knot nematode infestation are reduced vigor and yield, patches of unevenly sized trees, and characteristic galls on roots. Ring nematode infestation reduces tree vigor, and predisposes trees to bacterial canker complex, which can cause sudden collapse of trees in spring. Lesion nematodes reduce overall root presence and may cause reddish brown lesions on roots that later turn dark and ultimately black.