Success may mean soybean rotation

WOOSTER, Ohio — One of the best techniques a farmer can use to manage soybean cyst nematode is to rotate resistant soybean varieties, based on the preliminary findings of a Midwest soybean cyst nematode project.
Anne Dorrance, an Ohio State University Extension plant pathologist with the Ohio Agricultural Research and Development Center said the preliminary findings tells farmers that the recommendations by the OARDC to control soybean cyst nematode are on target and the date continues to emphasize the importance of sampling SCN population in the soil and manage the pest through the use of resistant soybean varieties.

Project complete

Dorrance and her colleagues analyzed Ohio soybean fields for the North Central Soybean Research Program regional project. They just completed year two of the three-year project.
The purpose of the project is to better understand SCN populations in Ohio and other regional states, as well as evaluate how soybean varieties with different sources of resistance respond to SCN populations.

Silent robber

Deemed the “silent robber of yields,” SCN is the No. 2 soybean pest in Ohio, behind Phytophthora sojae, which causes Phytophthora root rot. Soybean cyst nematodes feed on the roots of young plants, which prevents the roots from taking up vital nutrients. The result is a drop in yields and subsequent economic losses.
He said that the unique combination of genes developed for various PI88788 resistant soybean varieties offers varying levels of control for SCN.
For example, a variety with one set of resistance genes may give better control to SCN in one field, but not in another variety with a completely different set of resistant genes. “That’s why it’s key to rotate varieties with SCN resistance – to keep the pest guessing,” said Dorrance. “With weather conditions, field variations, plant performance, different gene packages and various SCN biotypes, a grower is not going to get 100 percent complete control out of one variety year after year after year.”

Recommendations

Dorrance recommends that growers work with their seed companies to make sure that they don’t plant the same resistant variety in the same field, giving the pest an opportunity to adapt. In the 2009 study, researchers planted five soybean varieties in three locations (Sandusky, Putnam and Shelby counties).
The varieties were replicated four times and planted in 200- to 250-foot strips and a soil sample was taken every 25 feet of each strip — 10 samples total. The fields were sampled at planting and before the soybeans emerged, as well as right after harvest so that the changes in SCN populations could be monitored during the season.

Key findings

In addition to the findings with resistant varieties, other key findings included:
• At the Sandusky location, uneven maturity keyed in on SCN presence. Stunting and uneven maturity are two key symptoms of soybean cyst nematode.
• The distribution of SCN in the test plots was very uneven. There were large pockets where there were no eggs detected and the next plot over contained 750 eggs per cup of soil,
• When SCN populations were high — greater than 500 eggs per cup of soil — varieties with Peking performed well. .
Dorrance said this was the first time in about 12 years that Ohio researchers have analyzed soybean cyst nematode so closely, and while much work still needs to be done to better understand the pest, the study reveals one unsettling truth: that SCN is widespread across the state and it’s not going away anytime soon.
For more information on SCN management, refer to the Ohio State University Extension fact sheet, “Soybean Cyst Nematode,” at http://www.oardc.ohio-state.edu/ohiofieldcropdisease/soybeans/AC_39_08.pdf, or go to the Plant Health Initiative Web site at http://www.planthealth.info/scn_basics.htm.