Mushy roots mean nematodes

Q. My onions look terrible. What’s wrong with them?

Bob from Ellsworth

A. Bob brought in onions that he had harvested from his garden that looked rotten. They had that characteristic brown, mushy look and smelled like they had rotted in the back of the pantry. I had my suspicions about the answer to his dilemma.

Upon examination under the microscope I found he had nematodes affecting his onions. These clear microscopic worms can be beneficial, while some may be harmful. These definitely were the harmful.

Once the soil has nematodes, it is important to do two things. First, do not plant onions, carrots, or any root crops, as well as some other plants that can attract them. Some of them eat on the outer edges of the roots, while others burrow into the plant roots and do extensive damage to the roots. This can cause stunted plants or wilted and dying plants, all due to the lack of nourishment that roots provide.

Second, after a diagnosis of nematodes, you must get rid of them. The type of nematode will determine the solution, but solarization is usually the best method. Solarization is a process where gardeners can use the sun to heat and kill all pests from the soil. It uses plastic over the soil. The plastic collects and holds the high heat to kill nematodes, fungi, spores, other insect pests and even weeds.

To do this, moisten the soil and cover it with a clear plastic tarp, burying the edges to pin it down. It takes the sunlight 4-6 weeks to sterilize the soil. Then, simply remove the tarp when you are ready to plant. Do not rototill or mix soil before planting.

In addition to solarization, gardeners should pay attention to other ways nematodes can get into the garden, according to Missouri Extension. All equipment, tools and anything used to start seeds for this garden should be thoroughly cleaned, then disinfected. New transplants should be inspected before placing them in the garden to check for “root-knot galls.” Finally, if making compost, Bob should ensure he gets the temperatures correct so his compost is done correctly. But, even if it is done correctly, nematodes may survive.

Other plants nematodes are drawn to are corn, potatoes, carrots, other root crops such as turnips, beets, rutabagas, parsnips, radishes, and of course, onions.

To learn more about nematodes and control of them in the home garden, go to http://go.osu.edu/nematode.

Stephanie Hughes is an OSU Extension master gardener volunteer in Mahoning County at the Mahoning Plant and Pest Clinic. Call the clinic at 330-533-5538 to submit your questions. Regular clinic hours are 9 a.m. to noon Mondays and Thursdays.