I had a client come in last week who has been having issues with extensive root damage on the plants in her gardens. The culprit? Nematodes. Nematodes are microscopic parasitic worms that live in the soil and can have a huge impact on plant growth and development. Georgia is one of the top 4 producers of fresh vegetables in the U.S., though this production is primarily in the southern end of the state. A 2018 study found that more than 60% of vegetable fields in Georgia contained root-knot nematodes.
Nematodes generally need three conditions to survive: water, high temperatures, and a suitable host. There are a variety of different types of nematodes including southern rootknot, peanut rootknot, soybean cyst, and sting others. Different nematodes have preferences for what plants they affect, what damage they cause, and what soil types they prefer. Nematodes damage plants by feeding on the roots, which inhibits water and nutrient intake, causes root swelling and galls, and stunts growth. Nematodes will cause localized patches of stunted plants in a garden or field. Plants are typically more affected during the seedling and establishment stages when they are developing their root systems. Most crops have an economic threshold above which the population level of nematodes is damaging enough to justify the cost of treatment.
The most effective way to tell if you have a nematode problem in your soil is to submit a nematode assay to the UGA Nematode Laboratory. It is important that you know the species of nematode you are dealing with. Typically, nematode tests should be conducted towards the end of the growing season or in the fall. Nematode populations will be highest at harvest and increase over the course of the growing season. Testing at the wrong time of year or not following proper testing protocols can result in an inaccurate test result. Nematodes can be hard to find and keep alive during transport to the lab. If you suspect a nematode problem, reach out to our office for help with sampling and testing procedures.
From a homeowner point of view, there are very few effective and economical ways of managing a nematode population. The two most effective ways of minimizing nematode issues are sun solarization and plant rotation. Plant rotation is simply the practice of not growing a susceptible host in the same site for more than one year. Moving the susceptible crop or the entire garden a few feet from its previous location can help reduce the overall nematode population. Rotation works especially well combined with the use of plant varieties that are resistant to nematodes. Some flowers, grains, and grasses do well as a rotational cover crop. The second method is sun solarization which harnesses the heat from the sun to kill soil-borne pests and nematodes. The soil should be tilled and worked thoroughly, moistened, and covered with a clear plastic tarp. The edges of the tarp should be weighed down or buried and left for at least 6-8 weeks. Do not remove the plastic until you are ready to plant. This process causes the sun to heat the soil, and the long-term high temperature exposure will kill nematodes, weeds, and other pests. Usually the disinfected zone is 6-8 inches deep. It is important that you do not mix or till the soil after solarization. Sun solarization is only effective in beds with full sun and is best done in the summer. The final treatment would be a chemical application- but there are very few economical nematicides available on the market to homeowners and a change in cultural practices is recommended instead.
