Soybean rust may have been the talk in crop fields across Ohio this season, but now is the time for growers to turn their attention toward a more elusive pest.

Deemed the "silent robber of yields," soybean cyst nematode may be in the shadow of soybean rust, but its threat is far more immediate. And soil sampling is the only way to identify its presence.

"Now is the best time to sample, right after harvest. The test is very simple and once you've got the number of soybean cyst nematode eggs, you're whole management plan is centered around that," said Dennis Mills, an Ohio State University plant pathologist with the Ohio Agricultural Research and Development Center. "It's not a big thing on the grower's mind, but it should be."

Soybean cyst nematode (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 generally shrug off SCN (only 3 percent of Ohio's fields have been tested, based on samples submitted to Ohio State's C. Wayne Ellett Plant and Pest Diagnostic Clinic). However, what growers don't know can hurt them, as the pest does its best work out of sight: stealing yields in such small amounts over so long a period of time that poor plant performance is blamed on other factors.

"With SCN, you don't see above-ground symptoms in Ohio. Growers just notice that their fields are not yielding as well as they have in the past," said Mills. "A grower may say, 'That field used to give me 70 bushels per acre, now I'm getting 55 or 60 bushels per acre.' Well that's kind of a telltale sign. Growers just don't know that SCN is there, unless they sample for it."

Mills said soil sampling is inexpensive, quick, and easy and is an accurate representation of any SCN activity in a grower's field. In order to prepare a soil sample, growers should collect 10-20 soil cores from a soil probe over a 10-20 acre area in any given field. Mix the soil together and send a composite sample to the C. Wayne Ellett Plant and Pest Diagnostic Clinic. The cost per sample is $15.

The results of the test produce the number of SCN eggs and the number of cysts present in the soil sample that was submitted. The number is then matched against a management chart developed by Ohio State Extension plant pathologists.

Yield loss threshold of SCN in Ohio begins at 200 eggs per cup of soil.
At 2,000 eggs per cup of soil, most susceptible soybean varieties suffer significant economic losses. At 5,000 eggs per cup of soil, growers should avoid growing soybean varieties altogether, even resistant varieties.

"For low egg levels, growers should use resistant varieties or rotate their crop. Fields with continuous soybeans year after year are the ones that have the highest SCN egg levels," said Mills. "One Ohio field we evaluated had egg levels of 40,000, which is double the maximum level, and that field had been in continuous soybeans for 30 years.
Yields in this field were in the teens. Without sampling, growers have no idea whether they have SCN and at what levels."

For more information on sending SCN soil samples to the C. Wayne Ellett Plant and Pest Diagnostic Clinic, call (614) 292-5006, e-mail ppdc@postoffice.ag.ohio-state.edu, or log on to http://ppdc.osu.edu. 
For more information on SCN, log on to http://agcrops.osu.edu/soybean/.