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Nematode-Caused Diseases
Nematodes are soil-dwelling, nonsegmented roundworms, usually less than 0.5 millimeters (0.02 inches) long. Those that feed on plants have a hollow, spear-like mouth part (stylet) that is pushed into the plant cell. The worm forces enzymes through its hollow stylet into the cells where cell components are digested and then drawn back into the nematode’s digestive system through the stylet.
The life histories and longevity of plant parasitic nematodes vary greatly from species to species. While some live inside host tissue and produce two or more generations per year, others live outside the plant and feed on outer cell layers, and others may have only one generation per year. Certain species lay hundreds of eggs in a season while others lay very few.
Those nematodes causing damage on woody ornamentals belong to the genera Meloidogyne (root knot), Criconemella (ring), Pratylenchus (lesion), Tylenchorhynchus (stunt), Paratrichodorus (stubby-root), Rotylenchus (reniform), and Xiphinema (dagger). Often more than one species is found associated with a plant’s roots. The effects of mixed populations of nematode species on woody ornamentals are largely unknown.
Always determine first whether the problem indeed is due to nematode activity. Many factors unrelated to nematode feeding can cause symptoms similar to nematode feeding. Both soil and roots should be sent promptly to the Penn State Plant Disease Clinic for analysis.
HS = highly susceptible (severe stunting, branch dieback, and death); S = susceptible (some stunting but plants will grow satisfactorily); T = tolerant (plants will grow satisfactorily); O = plants have not been tested
Adapted from R. K. Jones, D. M. Benson, and K. R. Barker. 1982. Nematodes and Their Control in Woody Ornamentals in the Landscape. Plant Path Info Note #63. Raleigh: Department of Plant Pathology, North Carolina State University.