| General Recommendations: Nematodes are tiny, microscopic roundworms. Most are soil dwelling where they live off fungi and bacteria and are not harmful to plant but a few are plant pathogens. Others are actually beneficial as insect-predators, used to help control insect pest such as Japanese beetle and other soil inhabiting grubs. About 40 species of plant-parasite nematodes have been reported in Missouri where they infest a wide range of plants. In addition to being plant pathogens in their own right, root-feeding nematodes can provide entrances to root rots and wilts. Some also transmit viral diseases.
Nematodes are grouped into several categories but those which are most often recognized by gardeners are the root-knot nematodes that infest plant roots and foliar nematodes that live in leaf tissue. Both often go undetected because of the nematodes microscopic size and the general nature of the symptoms they cause.
Root-knot nematodes infest plant roots either by feeding from the outside or actually entering the root tissue where they cause small growths, galls or knots on the roots. Above ground symptoms are generally characterized as poor growth and stunting which results from the plant's reduced root system and its reduced ability to take up water and nutrients. Wilting may occur during times of stress. Symptoms of nutrient deficiencies may also occur. Unless plants are removed from the ground and roots examined, poor growth due to nematodes may easily evade detection. Furthermore, galls on the roots of legumes (plants in the bean family) may be confused with nitrogen fixing nodules and vise versa. (To distinguish the two, nodules caused by nitrogen fixing bacteria are loosely attached and can be easily rubbed off whereas galls or knots caused by nematodes are actually part of the root and cannot be removed.)
Many trees, ornamentals, grasses and vegetables are susceptible to root-knot nematodes. According to the University of Missouri, some vegetable crops in Missouri that are most susceptible to root-knot nematodes are tomatoes, okra, beans, squash, peppers, carrots, cucumbers, muskmelons, eggplant and watermelons. Nematode damage also has been observed on Swiss chard, peas, parsnips, Irish potatoes, New Zealand spinach and fall-grown turnips and spinach. Plants that are fairly resistant include: broccoli, Brussels sprouts, mustard, chives, cress, garlic, leek, groundcherry and rutabaga. Other plants that grow well even when root-knot nematodes are present are globe artichoke, Jerusalem artichoke, asparagus, sweet corn, horseradish, some lima bean varieties, onion and rhubarb.
Established trees and ornamentals may live with root-knot nematode damage for many years with few signs of damage. Even if the plant dies from the nematodes during a period of stress the nematodes may escape detection unless the root system of the plant is dug up and examined.
Foliar nematodes can infest leaves, stems and buds of plants where they can cause deformed leaves or yellow to dark brown spots between major leaf veins. Many ornamentals are known to be attacked by foliar nematodes; some common plants include: hosta, Japanese anemone, chrysanthemum, azalea, and ferns. Positive identification of the presence of foliar nematodes can be made with the aid of a microscope after the nematodes have been "teased" out of living tissue placed in a petri dish of water.
A very serious pest of many conifers in Missouri, especially pines, is the pinewood nematode. For detailed information on this pest see the IPM sheet entitled "Pinewood Nematode Wilt of Needled Evergreen".
Control of Nematodes:
1. Do not plant stunted plants in your garden. Root-knot nematodes are difficult to control so the best recommendation is to keep them from getting into your garden in the first place. Granted, this can be difficult because detection may be difficult, but if you notice root knots on the root system you are about to plant in your garden think twice. Examine it closely for possible nematode damage.
2. Keep plants healthy. Nematodes may already be in your garden and you have lived with them for many years. Since plants are most affected in sandy soils and during periods of higher temperatures and low moisture, avoid having plants become stressed during these times.
3. Plant resistant vegetable varieties. If you have identified root-knot nematodes on a vegetable crop, look for resistant varieties. Tomato varieties with an "N" behind their name such as in VFN means the variety is resistant to nematodes.
4. Crop rotation. Though it may be difficult to do in a small garden, plant a crop in the infested area that is resistant to the root-knot nematode. Nematodes need live plant material to live on so if they do not have a suitable food supply their numbers will decline. This may take 3-5 years to be successful.
5. Soil solarization. Some success has been achieved by covering moist soil with clear plastic in full sun during the hottest part of the year to solarize the soil. By maintaining high soil temperatures for 4-6 weeks some success has been obtained.
6. Soil fumigation. Most chemicals used for soil fumigation are very dangerous if not used properly and may require a licensed applicator to apply. They are generally not a realistic alternative for home gardeners.
7. Practice strict sanitation for foliar nematodes. Foliage on plants infested with foliar nematodes should be collected and destroyed. Do not add them to your compost pile.
8. Interplanting?Though some gardeners advise that interplanting susceptible crops with marigolds will reduce damage from nematodes, this has not been borne out with research. In some cases it has been found that the marigolds actually attracted rather than repelled certain nematodes.
University of Missouri information: http://muextension.missouri.edu/explore/agguides/hort/g06204.htm
Nematode testing fees: http://soilplantlab.missouri.edu/nematode/ | 
