Root Knot Nematodes in My Beets

Root knot nematode damage on a Grex beet. PHOTO/Amy W.

Some of my fall-planted beets grew well and were large enough to harvest back in December. These didn't show any sign of nematode damage, so seeing masses of knotted roots when I pulled the last few beets last week was a surprise.
It hadn't occurred to me that root knot nematodes would affect my winter beets, even though I know that my garden is occasionally troubled by these pests, but the knots on the beet (from a packet of 3-Root Grex) pictured here show that winter barely slowed them down.

It probably didn't help that November and December were so warm; the ground didn't get good and cold until around mid-January.

Really, having had three wet/rainy years in a row didn't help, either. Nematodes are less likely to proliferate in drier soils. It also doesn't help that I've been bad about keeping the weeds out this winter. According to the University of Arkansas publication "Control root-knot nematodes in your garden", "Root-knot nematodes also feed and multiply on many garden weeds, although they may not injure these plants to any extent."

Since this nematode problem is unlikely to just go away on its own, I have developed a plan to bring the population down to a less-horrifying level. I've already turned the soil in the affected bed, to remove weeds and expose more nematodes to the cold, drying air. In a week or so, I'll repeat that activity, and then again a week or two after that. Normally, I would not want to disturb the below-ground community so much, but these, apparently, are desperate times.

After the soil-turning series, I plan to plant collard and mustard greens just as thickly as I can, since their presence suppresses root-knot nematode populations. A week before spring planting, which will rely on as many nematode-resistant varieties as I can find, I'll turn under those greens.

This plan will not make the nematodes go away, and I may need to work out some additional strategies to keep the momentum going. A big component will be keeping the weeds out. Wish me luck!

The good news is that not all garden crops are troubled by root-knot nematodes, and, according to a publication about nematodes by the University of California IPM Program, not only will resistant varieties of crops produce in spite of showing some galling in the roots, "An additional benefit of growing a resistant variety is the nematode levels in the soil decline rather than increase..."

Sounds good to me!

Benefits of Crop Rotation

I have understood for a pretty long time that crop rotation, which involves the practice of NOT planting the same crop (or crops in one plant family) in the same location year after year, is important for a variety of reasons.

One reason is that plants in one family often are attacked by the same pests and diseases. Rotating out of a particular space, and planting crops from a different family there instead, can help reduce the buildup of diseases and pests that attack crops in one plant family.

Another reason is that plants in one family often make similar nutrient demands on the soil. Jessica Strickland of North Carolina Cooperative Extension, in a May 2013 article, wrote:

"Vegetables in the same family are similar in the amount of nutrients they extract from the soil, so over time planting the same vegetables in the same spot can reduce certain nutrients in the soil. If the same family of vegetables is planted every year in the same location, insect and disease problems continue to increase and soil fertility drops. Using pesticides and fertilizer could provide little help but over time they would not be able to keep up with the increasing problems."

Also, rotating to some particular crops can help reduce a pest problem that already has built up to damaging levels. An example pest is root knot nematodes, which can lower productivity of a crop pretty dramatically - if they don't actually kill the plants outright. A population of these soil-dwelling pests can be lowered by planting a bed solidly in one of the nematode-repelling marigolds or in a grass-family crop like rye, wheat, or oats.

What I didn't know until recently is the effect of crop rotation on the diversity of soil microbial life, the maintenance of which is so integral to successful organic gardens. In the Science Daily article "Why crop rotation works: Change in crop species causes shift in soil microbes", Professor Philip Poole of the John Innes Centre in England is quoted as saying,

"Changing the crop species massively changes the content of microbes in the soil, which in turn helps the plant to acquire nutrients, regulate growth and protect itself against pests and diseases, boosting yield."

Professor Poole added: "While continued planting of one species in monoculture pulls the soil in one direction, rotating to a different one benefits soil health."

Yet another good reason to plan a careful rotation in the veggie patch.