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Rotation manages soybean yield robber

One of the best techniques a farmer can use to manage soybean cyst nematode is to rotate resistant soybean varieties, according to the preliminary findings of a Midwest SCN project.

“These preliminary findings tell us that our recommendations to control soybean cyst nematode are spot-on,” says Anne Dorrance, Ohio State University Extension plant pathologist. “The data continues to emphasize the importance of sampling SCN populations in the soil and managing the pest through effective use of resistant soybean varieties.”

Key Points

• Two years of study confirm that rotation best controls SCN.

• SCN is the No. 2 soybean pest in Ohio after phytophthora.

• It is important to sample for the pest in your soils annually.


Dorrance and her colleagues analyzed Ohio soybean fields for the North Central Soybean Research Program. 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 and to evaluate how soybean varieties with different sources of resistance respond to SCN populations.

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.

Controlling SCN

“Growers manage SCN first with crop rotation, then by planting different sources of resistance, such as PI88788, Peking or Hartwig,” Dorrance says. “Here in Ohio, growers most commonly plant varieties derived from the PI88788 source of SCN resistance. But what we found in the study is that varieties from PI88788 don’t always act the same.”

The unique combination of genes developed for various PI88788-resistant soybean varieties offers varying levels of control for SCN. For example, in a given field, a variety with one set of resistance genes may give better control to SCN than another variety with a completely different set of resistance genes.

“That’s why it’s key to rotate varieties with SCN resistance — to keep the pest guessing,” Dorrance says. “With weather conditions, field variations, plant performance, different gene packages and various SCN biotypes, a grower is not going to get complete control out of one variety year after year.”

Dorrance recommends growers work with seed companies to make sure they don’t give the pest an opportunity to adapt by planting the same resistant variety in the same field year after year.

Pollock writes for OSU Extension.

Findings from SCN research

In a 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. A soil sample was taken every 25 feet of each strip — 10 samples total. The fields were sampled at planting, before the soybeans emerged and right after harvest so the changes in soybean cyst nematode populations could be monitored during the season.

In addition to the findings with resistant varieties covered in the accompanying article, other key findings include:

• Uneven maturity keyed in on SCN presence at the Sandusky location. “As we looked across the susceptible strips, there were areas where plants were already mature and leaves defoliated, and other areas where plants and pods were still green,” says Anne Dorrance, Ohio State University Extension plant pathologist. “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,” Dorrance says.

• When SCN populations were high — greater than 500 eggs per cup of soil — varieties with Peking performed well. “However, before this becomes a recommendation, we need to get the fall SCN counts and see if the SCN populations declined when Peking was planted,” Dorrance says.

This is the first time in 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: SCN is widespread across the state, and it’s not going away anytime soon.

For more on SCN management, refer to the OSU Extension fact sheet “Soybean Cyst Nematode” at www.oardc.ohio-state.edu/ohiofieldcropdisease/soybeans/AC_39_08.pdf, or visit the Plant Health Initiative at www.planthealth.info/
scn_basics.htm
.


This article published in the January, 2010 edition of OHIO FARMER.

All rights reserved. Copyright Farm Progress Cos. 2010.