Every time a farmer doesn’t spray his peanut crop for southern corn rootworm, he can thank the research and Extension faculty at North Carolina State University and Virginia Tech. They’ve just saved him some money.
After studying more than 400 commercial fields in trials, research and Extension faculty at the two land-grant universities determined that most didn’t need to be treated for southern corn rootworm, long considered a major pest of peanuts.
The work resulted in the Southern Corn Rootworm Advisory. The bottom line: a $15 per acre savings by not treating when it’s not needed. The Advisory is accurate 98.5 percent of the time.
"The advisory is designed to help you know in two minutes whether you need to treat for southern corn rootworm," says Ames Herbert, Virginia Tech Extension entomologist. Herbert and Rick Brandenburg, North Carolina State University Extension entomologist, developed the risk index that now is known as the Peanut SCR Advisory.
Take the two-minute drill to determine if your peanuts are at risk from Southern Corn Rootworm damage.
Loam soil is at highest risk, at 15 points; loamy sand has the least risk at 5 points; and fine-loamy sand is the middle ground at 10 points.
Poorly drained soil has a risk of 20 points; well-drained soil has the least risk at 5 points; moderately drained soil is 10 points; and somewhat poorly drained soil has the highest level of risk at 50 points.
When considering the field history of rootworm damage, assign 5 points if there has been low incidence; 10 points for moderate; and 15 points for high incidence. If the history of the field is unknown, assume moderate damage.
If peanuts are planted before April 25, assign 5 points; if planted April 25-May 15, 10 points; and after May 15, 15 points.
Cultivar resistance plays a role as well. For NC 6, assign 5 points to the risk index; for VA 98R, 10 points; and for NC 10C, NC12C, NC 7, NC9, NC-V11, VA 93B, runners and other varieties, 20 points.
A score of 50 or less means a low risk to Southern Corn Rootworm. A decision to not treat in this scenario results in a savings of as much as $15 per acre. Experts advise scouting for leafhoppers and treating with a foliar spray if needed.
A moderate score of 55-65 means rootworm damage may not reach economically damaging levels. The treatment decision should be made based on weather conditions and land-lease requirements. Consider treating low areas in fields.
In wet years, treating before rain may prevent severe pod damage, even in late July. Also, scout for leafhoppers and treat with foliar spray.
A score of 70 or higher on the Advisory means a field is at high risk for Southern Corn Rootworm damage.
Treat all high-risk fields and all irrigated fields for Southern Corn Rootworm. Scout for spider mites.
The bottom line to all the research is, most fields don’t need to be treated.
"More than a decade of research and on-farm tests demonstrate that only a small percentage of the peanut acreage actually needs to be treated for southern corn rootworm," says Rick Brandenburg, North Carolina State University Extension entomologist.
Last year, the researchers extended the Advisory to include borderline fields, those described as poorly drained. That accounts for only 3 percent of the fields surveyed. Southern corn rootworms thrive in moist soils. In dry years, they recommend treating preventative on poorly drained soils after you get an inch or more of rain every week.