Selecting the right varieties

Pawel Wiatrak, Emerson Shipe, and Jason Norsworthy

Maximum yield potential can better be achieved if farmers choose nematode and disease resistant, and top-yielding varieties that match the soil, pest, and managerial (e.g., plant date) conditions imposed. Selection is complicated by the large number of varieties commercially available (100+). New varieties and promising breeding lines are annually evaluated in official Clemson University tests. Test locations are at the Pee Dee

Research and Education Center (REC) at Florence, Edisto REC at Blackville, and Calhoun Research Area at Clemson. Seed yield, plant height, harvest maturity, and lodging are measured for each variety. Researchers may also evaluate nematode or disease resistance at certain locations. Performance results are available both on the Internet and at County Extension offices. Farmers are encouraged to check the performance data when selecting varieties.

The following steps should be referenced when selecting varieties:

  • Select nematode-resistant varieties for fields where parasitic nematodes (soybean cyst, southern and peanut root-knot, Columbia lance, or reniform) have been identified as a problem.
  • Choose varieties (http://www.clemson.edu/edisto/soybeans/variety) that are high yielding over multiple years (environments) and locations.
  • Consider varieties with good tolerance to diseases, lodging, and shattering.
  • Select varieties appropriate for the time of planting [maturity group (MG) IV and earlier for April 15 through May 10, V to VI for May 1 through June 10, MG VII through MG VIII for June 1 through July 1].

If you have nematodes, the best variety won't yield well if it doesn't have resistance. There are some choices for root knot and other non-cyst nematodes. Maturity group is very important as well, especially when spreading risk is important or a grower is farming over large distances or in double-crop settings.

Roundup Ready (RR) varieties have been widely adopted in South Carolina, especially in fields with hard to control broadleaf weeds such as sicklepod or Palmer amaranth or in fields having herbicide resistant weeds (e.g. ALS-resistant pigweed and DNA-resistant goosegrass and pigweed). Since the release of RR varieties in 1996, farmer usage of this technology has increased annually, with 89% of the US soybean acreage planted to RR soybean in 2006.

Regarding the Roundup Ready (RR) soybean, choose varieties that are adapted to SC conditions and fit your farming operation. If you are double cropping with wheat, RR varieties from late MG VI through MG VIII are needed for best yield performance. Unfortunately, there are only a limited number of varieties available within these maturity groups. In addition, most of the RR varieties lack resistance to many of the nematodes common to SC. It is imperative that fields having a history of nematode problems not be planted to variety that lacks resistance to the nematodes present in the field.

If nematode infested fields are planted to nematode susceptible varieties and Roundup is used as the sole means of weed control, not only will yields be extremely suppressed from the nematodes, but weed problems will be exacerbated in field areas where soybeans are severely stunted or die as a result of the nematodes. If a RR variety with nematode resistance is not available, select conventional varieties that do possess resistance.

Select RR varieties that have good yield potential. Weeds are manageable using conventional herbicides; therefore, don't select a low yielding RR variety for the sole reason of controlling weeds. Consider using a soil-applied herbicide if you are using RR technology and planting in wide rows (see Soybean Weed Control section).