Nematodes and their control in
woody ornamentals in the landscape

Disease Information Note 63
D. M. Benson, Plant Pathologist

Figure 1. Galls on roots caused by root-knot nematodes.
Nematodes are one of the most destructive groups of pests causing decline of established ornamental plants in North Carolina. These microscopic roundworms feed on plant roots, causing various types of damage.  For example, root-knot nematodes cause swellings or galls on roots of susceptible plants (figure 1).  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 ornamentals in North Carolina.  Examples of plants which are severely affected are presented in Table 1.

Figure 2. Severe stunting of Japanese holly 'Helleri' (bottom) due to root knot nematodes. Compare to healthy plant (top).
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 dieback, failure to respond to fertilizer because of root damage and eventually death (figure 2). Symptoms of nematode damage usually are not apparent during late summer and fall or during extended dry periods.  Affected plants usually decline and die over a period of several years, but occasionally plants may die suddenly.

Other problems such as root rot or too much fertilizer can cause symptoms similar to those produced by nematodes. To determine the cause of plant decline, laboratory examination may be necessary. For laboratory examination, one should collect at least 1 pint of soil, plus some small fibrous roots, from several spots beneath affected plants and place in a plastic bag. Be sure to collect this sample from declining, but still living plants. The soil plus roots and some of the affected stems and leaves should be taken to your county extension office.

Nematode Control in the landscape

Presently, there are no effective chemicals registered for control of nematodes on existing landscape plants. Control of nematodes in the landscape must therefore be achieved by careful planning before planting.  Clandosan has given little or no control of nematode problems on established woody ornamental plants.

For existing landscape plants with nematode problems, it may help to mulch the plants, apply adequate water during dry periods, fertilize and lime properly, and prune out any dead branches. Plants already showing advanced stages of decline due to nematodes (50% or more of above ground portions of plant) should be replaced with less susceptible shrubs or turf.

For new landscape plantings or replanting, nematode problems must be avoided rather than corrected after planting.  Where possible, it is best to avoid using highly susceptible plants (Table 1) on sites where damaging nematodes are known to occur.   It is also very important to purchase plants free of damaging nematodes.

To determine if damaging nematodes are present in the soil before planting, collect a representative soil sample (1 quart) in a plastic bag from the area to be planted and take it to your county extension office. Check with your county extension agent for more details on the procedures, forms, fees, etc.

If damaging nematodes are known to occur in the planting site and highly susceptible plants must be used, the entire area can be treated before planting. Such sites may be treated with methyl bromide and chloropicrin (restricted use pesticide), or SMDC (Vapam). These chemicals cannot be used between existing plants in a bed. Chemical treatment is usually performed by trained professional applicators.

The following information is based on many years of field research conducted at the Central Crops Research Station at Clayton, North Carolina.

Table 1.  Reaction of some ornamental plants to various nematodes.

Host Plant Root Knot Stunt Lesion Ring
Azalea T S O T
Aucuba japonica HS S O S
Buxus microphylla (Japanese Boxwood) HS T O O
Buxus sempervirens (American Boxwood) O T HS O
Buxus sempervirens (English Boxwood) O O HS O
Camellia japonica T T O O
Camellia sasanqua T T O O
Gardenia jasminoides S T T T
Gardenia radicans HS T T T
Ilex cornuta (Chinese Holly)
cv.  Burfordi T T O T
cv.  Rotunda S S O S
Ilex crenata (Japanese Holly)
cv.   Compacta HS T T S
cv.   Convexa HS T O S
cv.   Helleri HS S O S
cv.   Rotundifolia HS S O S
Ilex vomitoria nana (Yaupon Holly) T T O T
Juniper sp.
cv.  Blue Rug T T HS T
cv.   Shore Juniper T T O T
cv.   Spivey Greek T T S T
Liegustrum (Privet) T T O T
Nandina domestica T T T T
Photinia fraseri (Red Tip) T T O T
Rose S S S T
HS - Plants highly susceptible (severe stunting, branch die-back and death)
S - Plants susceptible (some stunting but plants will grow satisfactorily)
T - Plants will grow satisfactorily
O - Have not been tested.

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Recommendations 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.  02/91/500

Published by North Carolina Cooperative Extension Service
Distributed in furtherance of the Acts of Congress of May 8 and June 30, 1914.   Employment and program opportunities are offered to all people regardless of race, color, national origin, sex, age, or disability. North Carolina State University at Raleigh, North Carolina A&T State University, U.S. Department of Agriculture, and local governments cooperating.

webpage updated Dec. 2000