Scout now for soybean cyst nematodes
A soybean plant seemingly suffering from nutrient deficiencies, diseases, herbicide injury or development issues due to compaction could be the victim of another more serious culprit: soybean cyst nematode.
Dennis Mills, an Ohio State University plant pathologist with the Ohio Agricultural Research and Development Center, said that now is the time to scout fields for the pest, specifically for females that may be feeding on plant roots.
"Soybean cyst nematode is an important soybean pest that often goes unnoticed or whose symptoms are mistaken for other plant problems," said Mills, who also holds an Ohio State University Extension appointment. "SCN can cause substantial yield losses, however, even without above-ground symptoms."
Mills said that growers can confirm SCN infestations in their soybean fields by digging up plant roots and shaking off excess soil. Females, if present on the roots, will be small, round, white-to-yellow objects about the size of a pinhead. Females will be present in fields now through early September.
"Although observation of the females will confirm a SCN infestation, it cannot tell you much about the level of infestation. If no nematodes are found that does not mean that SCN is absent," said Mills.
The best way to determine the presence of SCN and the level of infestation is to conduct soil samplinges in the fall after soybean harvest.
"Sampling in the fall will give an estimation of the population levels on which to base management decisions for planting next spring," said Mills.
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 follow these guidelines:
--Use a 1-inch diameter soil probe to collect soil samples (6 to 8 inches in depth).
--Following a zigzag pattern, collect 10 to 20 soil cores per 10 to 20 acres.
--Collect cores from areas of similar soil type and crop history.
--Dump cores from each 10-to 20-acre area into a bucket or tub and mix thoroughly.
--Place 1 pint (2 cups) of mixed soil in a soil sample bag or plastic zippered bag and label with a permanent marker.
--Store sample in cool, dark place until shipping.
--Send the composite sample to a lab doing SCN analysis, such as the C. Wayne Ellett Plant and Pest Diagnostic Clinic (http://ppdc.osu.edu).
Mills said that growers should take great care when preparing soil samples. Several environmental and biological factors exist that can cause variability of SCN populations and yield inaccurate sampling results. Such factors include SCN population patterns, soil structure, cropping history, timing of egg hatch, survival tactics, tillage, and the presence of alternate hosts.
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.
"The take-home management message is rotation, rotation, rotation," said Mills. "It's the most effective way of controlling SCN."
Currently, SCN is present in the majority of Ohio counties. Once infestation takes hold, it's almost impossible to rid the pest from a soybean field without intensive management practices.
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.
For more information on SCN management, refer to the Ohio State University Extension fact sheet, "Soybean Cyst Nematode," at http://www.oardc.ohio-state.edu/ohiofieldcropdisease/soybeans/AC_39_08.pdf.