Forest Health > Insects and Diseases publication
Tree Disease: Nematodes
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ROOT PARASITIC NEMATODES
Galls on roots of dogwood parasitized by the root-knot nematode, Meloidogyne incognita.
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| Pathogens: |
Various Nematodes |
| Common Host: |
Many Species of Trees
Figure 18- Illustration of how nematodes parasitize and damage roots. |
Significance: |
Several types of nematodes are parasitic on the roots of various plant species. These soil-borne parasites cause considerable damage to a variety of agronomic crops including citrus in Florida. Nematodes are perhaps best known to the backyard gardener by way of their ability to infect the roots of tomato plants and other garden favorites. Not a great deal is known regarding the effects of nematodes on trees. However, certain species of nematodes do infect the roots of various trees and can result in reduced vigor and stunting of infected hosts when infections are severe. Nematode infections rarely result in the death of infected hosts, but it is not uncommon for certain root disease fungi to infect nematode-damaged roots, resulting in further damage, and even mortality in some cases. Some nematodes serve as vectors (carriers) for certain plant viruses, carrying these infectious, sub-microscopic particles from host to host as they feed. Both conifers and hardwood are susceptible to nematode infections. |
Recognition: |
Most nematodes are invisible to the naked eye. Nematode damage is recognized primarily through observation of suspect trees, careful examination of their roots (especially the smaller, feeder roots), and analysis of the soil surrounding the roots. Definitive nematological evaluations are best performed in specially equipped laboratories by trained nematologists. In the field, nematode damage might be suspected when (a) trees exhibit poor growth and/or stunting, (b) foliage is chlorotic (pale or yellow) and smaller then normal, (c) smaller, feeder roots are necrotic (dead or dying), stunted, stubby, knotted (galled), or displaying definitive lesions, (d) other explanations for the poor performance of suspect trees are lacking. |
Infection Biology: |
Root parasitic nematodes are soil?borne, and although they migrate short distances within infected roots or infested soil, long distance movement occurs primarily through the movement of infected root material or infested soil. Many nematodes are capable of survival for several years in soil without suitable host root material on which to feed. When host plants are present and other conditions are suitable, nematodes reproduce, often completing several life cycles a year, and populations can quickly build up to damaging levels. Some nematodes (ENDOPARASITIES) feed on roots by actually burrowing into susceptible root tissues. Others (ECTOPARASITES)do not burrow into roots, but feed by piercing root cells with their retractable, needle-like mouthparts called stylets (see Fig. 18). |
Control: |
Control of root parasitic nematodes on established plants or trees is difficult to achieve. Maintaining host plants in a state of vigor by appropriate fertilization, watering, mulching, etc., is recommended, and in most cases such cultural practices are sufficient to enable the infected hosts to tolerate the parasites. Soil sterilization using methyl bromide or other appropriate soil fumigant (liquid or gas) is recommended when planting susceptible host species in soils with a history of nematode problems. Avoid movement of infected roots, infested soil, or contaminated equipment (shovels, roto-tillers, etc.) into areas where susceptible hosts will be planted. |
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Bulletin No. 196-A | Printed October, 1983 | Contact the Forest Health Section |
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