By Adriana Murillo-Williams and Paul D. Esker et.al.
Soybean cyst nematode (SCN, Heterodera glycines) is the most damaging soybean pest in the United States. In Pennsylvania, it was detected in Lancaster County in 2002, however, very little is known about its distribution across Pennsylvania. In the 2019 growing season, we have documented suspected fields with SCN in three counties. SCN easily spreads through anything that moves soil and infected roots; therefore, we recommend soybean farmers scout and take soil samples to know if SCN is present in their fields and at what population levels.
What should we be looking for?
Six weeks after soybean emergence is a good time to visually inspect soybean roots and look for soybean cyst nematodes (SCN) female bodies (Figure 1).
Figure 1. A) Soybean root with soybean cyst nematode (SCN) females and nitrogen fixing nodules. B) Close up picture of SCN female body with egg mass (Photo credit: G. Tylka, Iowa State University).
When scouting for SCN, dig out (do not pull) soybean roots from different areas in your field and look for the white, lemon-shaped female bodies protruding from the root. You can also target areas in the field where plants look stunted and yellow. When the SCN females die, their bodies filled with eggs (cysts) turn brown and detach from the roots. Therefore, for diagnostic purposes, we do not recommend relying only on visual examinations of roots. Whether or not you find SCN on the soybean roots, the next step is to collect soil samples and submit them to a nematology lab.
To collect samples for testing during the growing season, use a soil probe or a shovel to collect soil samples in the root zone (i.e., within the row). Collect at least 20 soil cores, with each one being 8 inches deep, for every 15-20 acres. There are different approaches to collecting soil samples. For example, large fields can be subdivided into 20-acre segments and samples collected in zigzag pattern, as shown in Figure 2.
Figure 2. Soil samples for nematode analysis can be collected using a zigzag pattern across the field (Photo credit: A. Murillo Williams, Penn State Extension).
Samples can also be collected from different management zones within the farm, like hillsides or along waterways. Sampling can target areas that are considered of high risk, including, field entryways, low spots, areas prone to flooding, along fence lines, low-yielding spots, near buildings where equipment is stored, and high pH areas. Some of these examples are shown in Figure 3.
Figure 3. Areas of high risk of SCN. A) Field entryway; B) Areas prone to flooding; C) Low spots, and D) consistently low yield areas (Photo credit: A. Murillo Williams, Penn State Extension).
In the field, nematode populations are quite variable. Therefore, take as many soil cores as possible, even in smaller areas or fields. Once you have collected the soil cores, mix them well, and put them in a soil sampling bag. Place the bag in the refrigerator (not the freezer) until the sample is shipped to the nematology laboratory of your preference. As a reminder, we offer a
free nematode testing program available for soybean farmers in PA thanks to the collective effort of Penn State Extension, the PA Soybean Board, and the
SCN Coalition. This is a great way to obtain useful information about your farm and fields to better manage those if SCN were to be detected.