Charles Overstreet, Xavier, Deborah
The Southern root-knot nematode can be a serious pest for many gardeners each year in Louisiana. This nematode attacks many of the plants that are grown in gardens but can be particularly destructive on tomato, okra, cucumbers, and melons. Although the nematode is most damaging during warm weather, it can be a problem during most of the year in our state.
The Southern root-knot nematode prefers soils that are fairly coarse including loamy sands, sandy loams, and some of the coarser silt loams. It is naturally found in many of these soils across Louisiana. It is also very easy to bring this nematode into the garden from contaminated plants or equipment such as trowels, shovels, or tillers from one location to another. The Southern root-knot nematode cannot withstand drying but can be spread on fresh soil attached to equipment. Once this nematode has entered a location, it becomes extremely difficult to eliminate.
Resistant varieties are available from several vegetables that are grown in the garden including tomato, cowpeas, and bell pepper. Resistant tomato varieties to our common root-knot species include Better Boy, Big Beef, Terrific, Amelia, Floramerica AAS, and Mountain Fresh Plus. Cowpea varieties with resistance include Mississippi Silver and Mississippi Purple. Clay/Iron are cowpea varieties that are used as a cover crop and also very effective against Southern root-knot. Carolina Wonder and Charleston Belle are pepper varieties which have strong levels of resistance to root-knot nematode.
How effective are these resistant varieties against nematodes under Louisiana conditions? The figure above shows the root systems of a root-knot resistant and susceptible tomato grown side-by-side in garden bed. There were four plants of each variety in the bed. All of the susceptible plants were severely galled by the Southern root-knot nematode. The galls are swellings of the root system around the nematode. Larger galls indicate multiple nematodes in the same area. However, the resistant plants had very low or no detectable galls on any of the four plants. Usually, plants that are severely galled by this nematode yield poorly or don’t last very long. Although the resistance in tomatoes or peppers may be reduced when soil temperatures get very high in the middle of our summers, the resistance usually holds up well in the spring with cool soils and fall as soil temperatures are decreasing.
The picture above also indicates that planting resistant and susceptible plants in the same area will not work. Although the nematodes that enter into the roots of the resistant plant may be killed, those that enter the susceptible plant continue with their life cycle and build up large numbers in the soil. It is always better to plant the area solid with the resistant plants to reduce the numbers of root-knot nematode. Although there currently are only limited vegetables in the garden with root-knot nematode resistance, using resistance can certainly help reduce problems from this pest.