The most important species of root-knot nematode in Florida are Meloidogyne incognita, M. arenaria, M. floridensis, and M. javanica. Problems result from root dysfunction and reduced root volume, which affects the uptake of water and nutrients. Yield reduction can be dramatic. In addition to the direct crop damage, infected plants may be predisposed to attack by fungal or bacterial pathogens that contribute to additional yield reductions.
Symptoms of root-knot injury are visible in both above-ground and below-ground plant parts. Above-ground symptoms include stunting, wilting, chlorosis, and other symptoms characteristic of nutrient deficiency. Affected plants usually occur in patches in a field. Below-ground symptoms consist of swollen areas (galls) on the roots of infected plants. Galls may range from a few swellings to extensive areas of elongated, convoluted, swellings, which result from multiple and repeated infections.
In general, the presence of root-knot nematode suggests a potentially serious problem. The extent of damage varies with host, timing of infection, and cultural conditions.
Survival And Spread
Root-knot nematodes have a simple life cycle consisting of egg, larvae, and adult. Larvae infect plant roots and take nutrients from the plant, causing the characteristic knots or swellings to form. Females may produce upwards of 2,000 eggs. Under suitable conditions, root-knot nematodes complete their life cycle within four to eight weeks. Development is most rapid when soil temperatures are from 70°F to 80°F.
Relative population levels and field distribution can be determined by examination of the crop root system for root gall severity. Immediately after harvest, a sufficient number of plants should be carefully removed from soil and examined to characterize the nature and extent of the problem within the field.
In general, populations increase with root gall severity. Such sampling can provide immediate confirmation of a nematode problem and allows mapping of current field infestation.
Nematode management in vegetables currently consists primarily of the use of pre-plant broad-spectrum fumigants to reduce nematode populations. For crop rotation to be effective, crops unsuitable for nematode must be introduced into the rotation sequence. Two leguminous cover crops adaptable for managing soil populations of sting or root-knot nematode include hairy indigo and American jointvetch.
Clean fallow during the off-season is probably the single most effective cultural control measure available for nematode control. When food sources are no longer readily available, soil population densities of nematodes gradually decline.
Recently, MeloCon WG (Certis), a biocontrol agent containing spores of the naturally occurring fungus Paecilomyces lilacinus, has been introduced on the market which has been used successfully to control nematodes in some instances.
By Gene McAvoy, Regional Vegetable Specialist IV, University of Florida/IFAS