Posted 16 December 2009. PMN Crop News.
Study Sheds More Light on Managing Soybean Cyst Nematode
Source: The Ohio State University Press Release. www.oardc.ohio-state.edu
Wooster, Ohio (December 7, 2009)--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.
“These preliminary findings are telling us that our recommendations to control soybean cyst nematode are spot-on, and the data continue to emphasize the importance of sampling SCN populations in the soil and manage the pest through effective use of resistant soybean varieties,” said Anne Dorrance, an Ohio State University Extension plant pathologist with the Ohio Agricultural Research and Development Center.
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.
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.
“Growers manage SCN first with crop rotation, then by planting different sources of resistance, such as PI88788, Peking or Hartwig,” said Dorrance. “Here in Ohio, growers most commonly plant varieties derived from the PI88788 source of SCN resistance. But what we found out in the study was that varieties from PI88788 don’t always act the same.”
Dorrance 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.”
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.
In addition to the findings with resistant varieties, other key findings included:
• At the Sandusky location, uneven maturity keyed in on SCN presence. “As you 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,” said Dorrance. “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,” said Dorrance.
• 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,” said Dorrance.
Dorrance said that 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 www.oardc.ohio-state.edu, or go to the Plant Health Initiative Web site at www.planthealth.info.