From Farmgate.com (U of I’s new agricultural blog): The purple deadnettle thriving in your fields this winter has a nasty secret just discovered by agronomists at Purdue. Those cute little plants, which some Master Gardeners will sell to each other at their spring plant sales, have been found to serve as hosts for soybean cyst nematodes when there are no soybeans in that field; either during the winter or when the field is planted to corn. “SCN infests purple deadnettle roots, just like they do on a susceptible soybean variety,” said Bill Johnson, a Purdue weed scientist. To protect soybean plants from the pest, researchers are trying to find the best timing to control purple deadnettle to reduce nematode densities.

You probably knew that since SCN likes soybeans, other legumes might be good hosts, and they are, indeed. The University of Missouri provided the following list of SCN hosts:

Beans (snap, bush, green, mung, kidney); BurcloverBirdsfoot trefoil; Clover (alsike, crimson, scarlet); Common and mouse-ear chickweed ; Common mullein ; Cowpea ; Ground cherry ; Hemp sesbania ; HenbitHop clover ; Lespedeza ; Lupine, white and yellow ; Peas ; Pokeweed ; Purslane ; Spotted geranium ; Sweet clover ; Vetch (common, hairy, winter, crown) ; Winged pigweed.

So now you can add purple deadnettle to that list.

But, let’s address a different issue. SCN is in the soil. Out of sight. Out of mind. Right? Maybe so, but you can add “out of wallet” to that axiom. The United Soybean Board says, “In fact, soybean cyst nematodes (SCN) are the biggest yield-reducing pests each year for soybeans. According to checkoff funded-research, yield losses from SCN can vary year to year from about 100 to 150 million bushels.

“SCN has such an impact on crop yield due to the longevity of the pests, which can survive in the soil for 10 years, feeding on soybean plant roots, damaging plant growth and laying eggs. The lemon-shaped nematodes vary in color from white to brown, and their eggs hatch into larvae, which mature within 14-21 days, resulting in rapidly increasing population growth. Fifty SCN eggs at the beginning of the season can develop into 15,000 eggs by the end of the growing season.”

As you know, those eggs are on soybean roots; and when is the last time you looked for them? Iowa State Extension agronomist Palle Pedersen pleads with farmers to look at their soybean root systems, just as you look for corn rootworms. He writes, “I don’t think it is an overstatement when I say that many of us have not thought too much about soybean roots. Soybean roots serve as major vegetative organs supplying water, minerals, and substances essential for plant growth and development. Despite these vital contributions, roots are often taken for granted because they are not visible. But, why?

“Is it because you do not make much money on soybean, anyway, so you don’t want to deal with it? Or is it because you don’t want to get out of your truck, away from the AC and get dirty? Or…., yeah I think that I have heard all the excuses. However, I know that many farmers dig up corn roots every year to look at root worm feeding. So why ignore soybean?”

Now that you have been stirred to do something, you need to focus on managing your SCN problem and promise your spouse to make more money for her next year. Let’s look at how to do that. The University of Missouri says you need to know that SCN is difficult to manage

•SCN can survive in the soil under adverse conditions within cysts.
•SCN lives in the soil environment, which is difficult to manipulate.
•Plant resistance to SCN is not complete.
•SCN can reproduce on at least 97 legume hosts and on 63 other plant species.
•Because of its adaptability, SCN can build up on previously resistant varieties.
•SCN can be suppressed but not eliminated.

Infested fields
•Rotation: Rotate soybeans with crops that are not SCN hosts. SCN cannot reproduce if host plants are not present. Rotate sources of genetic resistance in soybean varieties if possible. A certain percentage of SCN individuals can reproduce on resistant varieties. If sources of resistance are not rotated, these individuals can produce a SCN race shift. This will reduce the effectiveness of genetic resistance available in commercial soybean varieties.
•Maintaining plant health: Plant stress from drought, nutrient deficiencies, weed infestation, insects, and other plant diseases will aggravate plant damage caused by SCN.
•Resistance vs. nematicides: Resistant germplasm is more reliable and cost-effective than nematicides in reducing SCN populations.
•Weed control: Reduce weeds in fields, because weeds can also be SCN hosts.

You first need to know your SCN pressure, and that requires a soil sample that is best taken now. University of Illinois Extension says, “The recommendation to sample in the fall is not just for convenience. The population density of SCN in a cornfield at corn harvest is highly predictive of the numbers of SCN that will be present in the spring, because overwinter survival is very high.” University of Illinois nematologist Terry Niblack says “A soil sample should be a composite of 20 or more cores taken in a zigzag pattern across a field. Most nematologists agree that one sample can adequately represent a 5-acre area; some say as high as 20 acres. So what do you do if the field is 300 acres? Collect samples from two or more arbitrarily selected 5-acre sections that represent similar soil types and crop histories. There’s no need to sample the entire field unless you’re planning to plant different varieties in different sections of the field.” She recommends that you follow prescribed instructions for sampling.

After you know your SCN pressure, look for resistant varieties of soybeans. Seed selection is key, says University of Illinois Extension, which provides a website that lists resistant varieties for soybean groups 0 through 8.

Summary:
Instead of SCN stealing your money next year, try to keep your hard earned funds by determining how much of a problem you have with soybean cyst nematode, then doing something about it. Now is the time to collect soil samples, and make seed selection based on your needs for resistance. It is also time to control some of those winter annual weeds, such as purple deadnettle, that have been found to be a host for SCN until soybeans again are planted in that field.

Stu Ellis

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