As we all know this winter has been very mild in Central and Northern Missouri. If the ground froze at all this winter, it would have been at most a few inches only. This could be a problem. Southern Root-Knot nematode (Meloidogyne incognita) cannot survive a hard freeze, and this is the reason why it is usually not a problem in Central and Northern Missouri. Without getting a hard freeze down to 12-15 inches like we experienced during the mild winter last season, eggs of Root-Knot nematode most likely survived, and will hatch after the soil warms.
Since this pest is not commonly found this far north, it is present in gardens only where someone has inadvertently brought it. This nematode can only travel in soil or plant tissue. A tablespoon full of infested soil may contain tens of thousands of microscopic worms or eggs. For example, tomato seedlings received from Uncle Joe down south may be an entry point for this disastrous pest. It can also travel on bits of soil left on tillers or garden tools. Even dirty tires and boots can be a source of infection. Compost shared by a neighbor may also be a source, if the compost pile was fed with infested plant tissue and hadn't been properly turned.
We know from a study conducted a few years ago that Root-Knot is present in gardens in central Missouri. In Columbia six of the nine community gardens tested were positive for Root-Knot. We found that community and public gardens were more apt to have the pest than family gardens simply because more people were working these plots, and they were sharing equipment and compost. So the chance of spreading this pest is higher in a community garden.
Once the Root-Knot nematode has found a new home, it will happily feed on the roots of most garden plants. In fact it has over 2000 hosts. There is little you can do to control this nematode in your garden other than waiting for a good hard freeze the next winter. If your garden is free of this pest, the best thing to do is to practice good garden hygiene. Only use plants that come from reputable nurseries, or garden store and be sure that any borrowed garden equipment is cleaned of all dirt before using in your garden. Also make sure that any top soil or compost you use in your garden comes from a clean source.
Most people probably don't know if their garden has Root-Knot or not. Some plant symptoms of this pest are stunting, yellowing, and the tendency for the plant to wilt in the summer heat, even when there is plenty of moisture present. Vegetables yields may be reduced, due to fewer number, smaller size, and poor quality. A good way to determine if these symptoms are caused by the Root-Knot nematode or something else is to sacrifice a plant. Pull up a suspect plant and carefully observe the roots for bumps or galls (knots) that are caused by the nematode. These galls actually contain female nematodes that have swollen into spiracle shapes and laid hundreds of eggs in masses on the surface of the galls. These galls partially block the movement of water and nutrients through the vascular system of the plant, causing the symptoms mentioned above.
If you don't want to sacrifice a plant, simply wait until the end of the growing season. When cleaning up the garden, carefully check the roots of the old plants before discarding. Tomato, pepper, cucumber and most garden plant roots should be smooth. If they have big knots or galls along them, it is likely that your garden has become infested. In this case destroy all root material, and then remove any surface mulch or plant residue from the garden. Fall tillage may help by allowing cold temperatures of winter to penetrate more deeply into the soil, killing any Root-Knot eggs that may be present.
Another way to determine if you have this nematode is to take some soil plugs around plants showing symptoms and sending the sample to the University of Missouri Extension Nematology Lab for analysis. This $20 test will list all the different plant parasitic nematodes present and their numbers and comments. (Submit samples to: Extension Nematology Lab, Rm. 23, Mumford Hall, Columbia, MO 65211 with the sample submission form and the payment due).
Although managing Root-Knot nematode in the garden is extremely difficult, southerners have been dealing with this pest for many years and have developed some strategies. For management information see Missouri Environment & Garden, April 08, Vol. 14, #4, "Be Aware of a Potential Enemy in the Family Garden," or the MU Guide #G6204, "Managing Nematodes in Gardens."
Information on submitting samples to the Extension Nematology labs and sample submission forms can be obtained by visiting the lab's website at URL: http://soilplantlab.missouri.edu/nematode or by calling 573-884-9118.
REVISED: April 30, 2012