Institute of Food and Agricultural Sciences
Hendry County Horticulture News
Nematodes Can Be Bad News
Nearly everyone who gardens in Florida eventually has problems with nematodes. Nematodes are microscopic, round worms. There are several thousand different types of nematodes, which can be found in every environment. Only a small percentage of these are parasitic on plants. The nematodes which attack plants are aquatic animals that live in the moisture on soil particles or in plant tissue. Nematodes that affect plants must feed on living plant tissues to survive.
Plant parasitic nematodes can be divided into two types. Those that always live outside of the roots and feed only on tissues on the exterior of the root and those that spend at least a part of their life cycle inside the roots on which they feed.
Although nematodes cannot be seen with the naked eye, gardeners can easily learn to recognize the damage they cause to plants. Several symptoms may lead to the suspicion that nematodes are present. Above ground symptoms of nematode infestations are similar to those produced by many kinds of root injury. Foliage often displays premature wilting in response to heat and moisture stress. Prolonged stress arising from nematode injury to roots may result in yellowing and eventual loss of foliage. New growth may appear weak with fewer and smaller leaves than healthy plants. The lack of vigor may persist despite the application of additional fertilizer and water. The damage caused by nematodes usually shows an irregular pattern corresponding to the irregular distribution of the nematodes in the soil itself.
Below ground symptoms of nematode infestations vary widely. Some kinds of nematodes, such as root-knot nematodes, produce easily recognizable symptoms. These make their presence known by producing galls or knots on the roots of many plant species. Other structures such as the nitrogen-fixing Rhizobium nodules on beans and other legumes resemble root-knot galls and are often mistaken for root-knot. Root-knot galls are firm and have a solid interior. Attempts to remove a root-knot gall from a root will tear the root tissue.
Although root-knot nematodes are the most widely distributed nematode species in Florida, the less obvious root symptoms produced by other nematodes are often overlooked or confused with other root problems. Short, stubby roots with swollen tips, stunted roots, dark discolored roots and root decay often indicates the presence of other nematode species. A soil analysis is the only positive way to identify the presence and types of nematodes associated with a particular problem. Laboratory analysis of soil for nematodes can be arranged through the Hendry County Extension Office.
Many popular ornamentals are susceptible to nematode infestation. These include many hollies, ixora, hibiscus, Barbados cherry, ti plant, gardenia, boxwood, rose, and figs. Other species such as citrus and wax myrtle, may become more susceptible if exposed to stress from pests or environmental factors. Many annual flowers and vegetables also suffer from nematodes.
It is important to realize that parasitic nematodes are present in almost all Florida soils. With proper precautions, it is relatively easy to establish and maintain plantings despite the presence of parasitic nematodes. Good site preparation gives plants a chance to become established rapidly with a minimum of stress. Old roots and plant debris should be raked up and removed when preparing soil for planting. Organic amendments, such as compost, incorporated into the soil before planting increases the water and nutrient holding capacity of the soil enhancing plant growth and establishment and the activity of the naturally occurring enemies of nematodes in the soil. Use of mulches will create a healthy root environment increasing a plants ability to withstand nematode attack.
If nematodes have been known to be a problem in the past or highly susceptible plants are to be grown, soil treatment may give plants a better chance. Unfortunately, all available chemical treatments and soil fumigants must now be applied by a properly licensed pesticide applicator. Alternative products, such as nematode attacking fungi and various other bio-nematicides are available to the public and may give some protection against nematodes. Soil solarization is a relatively new technique, which involves covering moist soil with clear plastic sheeting. The high temperatures that are produced in the soil under the plastic have been shown to be effective in reducing nematode populations. Plastic should be applied at the hottest time of the year and left in place for 4 to 6 weeks to bake out nematodes.
Crop rotation and use of non-susceptible cover crops are particularly useful techniques available to vegetable gardeners. Where possible it is advisable to avoid nematode susceptible plants on soils where nematodes are know to be a problem. A number of tomato cultivars and woody ornamentals are known to tolerate nematode infestations.
Any condition, including pests or environmental
stress, that weakens plants may render them susceptible to nematodes
that they had co-existed with for years. Fertilize as needed to maintain
plant health and vigor. Water deeply to promote the development of a large
root system that can better withstand nematode damage. Providing
optimum care to your plants will help them resist attack by nematodes.
Good luck and good gardening.
Gene McAvoy is the horticulture agent with the Hendry County Extension Service. Direct your horticulture questions to PO Box 68, LaBelle, FL 33975, e-mail - firstname.lastname@example.org or phone 863-674-4092 or 863-983-1598. You are also welcome to visit the Hendry County Extension Office at 225 Pratt Blvd., LaBelle. Office hours are from 8:00 - 5:00.
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