Wooster, Ohio
October 18, 2007
Fall is here and the time is near
to soil sample for soybean cyst nematode (SCN).
The pest, which has a firm hold in Ohio fields, can damage
soybean plants and quickly depress yields if not managed
properly. The best way to begin managing SCN is to determine
population levels through soil sampling.
“To effectively manage SCN, you need to know which fields have
nematodes and how many nematodes are present,” said Dennis
Mills, an Ohio State University
plant pathologist with the Ohio Agricultural Research and
Development Center. “Sampling in the fall will give an
estimation of the population levels on which to base management
decisions for planting next spring.”
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.
“With SCN, you don’t always 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 follow
these guidelines:
- Use a 1-inch diameter soil
probe to collect soil samples (6-8 inches in depth).
- Following a zigzag
pattern, collect 10-20 soil cores per 10-20 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),
where the cost per sample is $15. Results report cyst counts
per 100 cc of soil.
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.
“Now is the best time to sample, right after harvest. The test
is very simple and once you know the number of soybean cyst
nematode eggs, your whole management plan is centered around
that,” said Mills.
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.”
For more information on SCN management, refer to Ohio State
University’s Department of Plant Pathology Ohio Field Crop
Diseases Web site at
http://www.oardc.ohio-state.edu/ohiofieldcropdisease/soybeans/scn.htm. |
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