Nematodes and Their Control on Woody Ornamentals in the Nursery
OD5 - Ornamental Disease Note No. 5
R. K. Jones, Extension Plant Pathologist
D. M. Benson, Plant Pathologist
K. R. Barker, Plant Pathologist
Nematodes are one of the most destructive groups of pests causing decline of establish woody ornamental plants in North Carolina. These microscopic roundworms feed on plant roots, causing various types of damage. For example, root-knot nematodes cause swelling or galls on roots of susceptible plants. Other types of nematodes cause plant roots to be stubby and branch abnormally. Nematode-damaged roots often are further destroyed by fungi and bacteria.
Several plant-parasitic nematodes such as root-knot, stunt, ring, sting, lance, lesion, stubby root, dagger and spiral have been associated with decline of woody ornamentals in North Carolina. Examples of plants which are affected by various nematodes are presented in Table 1.
Damage to plants from these root-feeding nematodes is progressive and often results in poor growth, low vigor, yellowing or bronzing of the foliage, loss of leaves, stem die-back, failure to respond to fertilizer because of root damage and eventually death. Death of nematode damaged plants often occurs during or following drought or cold injury. Extensive root damage has often occurred before above ground symptoms become obvious on established woody plants.
Nematodes are a problem in some nurseries in North Carolina, particularly with field grown plants. Nematodes should seldom be a problem in bark container mixes. A lack of uniformity in growth rate is often the main symptom. The nematodes not only damage the plants in the nursery, but are transplanted with the shrub into the landscape. Many nurserymen do not recognize nematode damage on their plants.
Nursery plants should be grown totally free of parasitic nematodes. Prevention of nematode damage must begin when the cuttings are first stuck and continued until the plants are sold.
Nematode damage rarely occurs in container grown plants. All soil, rooting media, or potting mix should be free of nematodes before planting. Sand, peat, bark, vermiculite and perlite are usually free of nematodes when delivered to the nursery. They must then be stored at the nursery so they will not become contaminated with nematodes in surface run-off water. Any soil to be used in a potting mix should be treated with methyl bromide at the rate of 2 pounds per 100 cubic feet or steam before mixing with other media components.
Field sites for growing woody ornamental plants should be sampled for nematodes in the fall before planting. See your local County Agent for information and costs for submitting samples to the North Carolina Department of Agriculture Nematode Advisory Service Laboratory. If the selected field has a nematode problem based on the laboratory report, choose another field free of nematodes or use a preplant soil fumigant such as SMDC (Vapam), methyl bromide chloropicrin mixtures. For more information on soil fumigation see Plant Pathology Information Note No. 170.
1. Response of Selected Woody Ornamentals to Nematodes.
HS - Plant
highly susceptible (severe stunting, branch dieback and death); S - Plants
susceptible (some stunting); T - Tolerant plants, will grow satisfactorily;
O - Have not been tested
with a specific problem, contact your local North
Carolina Cooperative Extension Service
of specific chemicals are based upon information on the manufacturer's
label and performance in a limited number of trials. Because environmental
conditions and methods of application by growers may vary widely, performance
of the chemical will not always conform to the safety and pest control
standards indicated by experimental data. All recommendations for pesticide
use were legal at the time of publication, but the status of registration
and use patterns are subject to change by actions of state and federal
regulatory agencies. 04/91/1000