The weather was a big variable across the Midwest this year. In Ohio, for example, some areas got heavy weekly rains while there was severe drought in other portions of the state.
"Soybean cyst nematode seems to do well under both conditions, but we see greater impact when the dry spells are longer," says Ohio State University pathologist Anne Dorrance.
Over the past 2 years, Ohio State has participated in the North Central Soybean Research Program funded regional soybean cyst nematode (SCN) project. In this study, five soybean varieties were planted in two locations during 2008 and three locations during 2009 to better understand SCN populations, and to get some local data on how these varieties were responding to SCN.
This year, Dorrance says the fields that were selected had very low to negligible SCN populations, but they still saw effects. In particular for soybean cyst nematode counts from the spring soil collection, our Sandusky field average ranged from 0 to 767 eggs per cup of soil while the Putnam location had 0 to 20 eggs per cup of soil.
Dorrance lists a number of key findings about SCN from the field research.
1. At the Sandusky location, the key symptom was uneven maturity. "As you looked across the susceptible strips, there were areas where plants were already mature and leaves defoliated — no sudden death — and other areas where plants and pods were still green. Stunting and uneven maturity are two key symptoms of soybean cyst nematode."
2. The distribution of SCN in field plots was very uneven. There were large pockets where there were no eggs detected and the next plot had 750 eggs per cup of soil.
3. The varieties yielded quite differently. When SCN populations were high, the two varieties with resistance from PI88788 had significantly different yields. "We’ve heard about this, where the varieties that were developed from PI88788 don’t always act the same," Dorrance says. "The resistance in PI88788 for SCN comes from five to six different genes. In each new variety, they all have the main gene, but they also have a different set of the additional genes. This is why we can sometimes see that one variety with PI88788 may give better control to SCN in one field but not in another. It is key then to rotate varieties with SCN resistance to keep SCN guessing."
4. When SCN populations are high — greater than 500 eggs per cup of soil — varieties with Peking did very well. "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.
While Dorrance says there is more data to analyze and soil samples to count, they are gaining a much better understanding of SCN in Ohio.
"It is taking yield," she says. "There was a 21% loss in yield at the Sandusky location when the susceptible variety was compared to the best resistance line. The only symptom was uneven maturity."