Submitting a soil sample for SCN diagnosis is the best step to take towards effective pest management. However, a diagnosis is only as good as the sample provided. Follow the guidelines below to receive the most accurate results.
Hand-out Materials Available for Distribution
Why sample for SCN?
The soybean cyst nematode (SCN), Heterodera glycines, is the most economically important pathogen of soybean in North America. SCN is distributed throughout the soybean production areas in the United States. Annual soybean yield losses due to SCN are estimated at approximately $1.5 billion.
In a recent Ohio survey, soil samples were collected throughout the state; over 80% of those sampled fields tested positive for the presence of SCN (Fig. 1). More than 75% of the growers from those fields were not aware they had this problem.
Classic symptoms such as stunted plants with chlorotic (yellowing) foliage may be observed only when SCN populations are high. These symptoms occur most often in fields with nutrient deficiencies and/or stressful environmental conditions (such as high temperature and drought). Most of the time, however, SCN infection causes no visible symptoms.
The fact that significant yield reduction may take place with absolutely no above-ground symptoms is one of the main reasons one must sample fields for the presence and abundance of SCN. The SCN presence and population levels are important information to make management decisions.
When should I sample?
Soil sampling is subject to weather conditions. Avoid sampling frozen, very wet or very dry soils. During the soybean growing season, the SCN population density fluctuates as juveniles emerge from the cysts to invade plants and new cysts are formed. In the soil profile, SCN is more abundant in the top 6 to 8 inches (15 – 20 cm) of depth. Soybean yield reduction due to SCN is related to its initial population density, that is, the number of eggs present in the field at planting.
The optimal window of time in which to monitor SCN population density is from one week before harvest until the ground freezes. At this time, the SCN population density is a good indicator of the next season’s initial population (Pi). Sampling before winter will allow time for nematology laboratories to process the sample and provide results for management decisions, such as selection of cultivars resistant to the specific SCN population in that field. Sampling in the spring can be done, especially in years where sampling was not conducive the fall before. SCN numbers will change as there is some winter kill of eggs.
If the purpose of sampling is diagnostic, to identify the presence of SCN in fields with no previous record of it or to conduct a survey to determine its distribution in a region, then sampling for SCN at any time is suitable. There are specific locations within the field to sample for SCN when its presence is suspected (see next section).
Where should I sample?
Diagnostic samples, to determine presence of SCN, should be taken from the following areas: any field areas that have been low yielding (use GPS from yield maps); pockets where soybeans mature early; areas with the presence of sudden death syndrome; places subject to flooding; entrances and borders of fields; and anywhere pH of soil is alkaline (pH higher than 7). Collect 6 to 10 soil cores from the root area of the plant, pool the cores and submit to a SCN testing lab.
To monitor overall populations to make management decisions, it is important to know that in SCN-infested fields, the nematode spatial distribution is concentrated in pockets (“hot spots”) and is not evenly distributed across the field. To estimate the average number of SCN eggs, a composite sample is collected from soil cores across a 15 to 20 acre (6 to 10 ha) area of the field (see Guidelines for SCN Soil Sampling below).
SCN is an obligate sedentary parasite; it will remain at the same feeding site on the root for the rest of its life. We find more SCN in the rhizosphere (root zone). If soybeans were severely stunted, sampling in the transition zone between healthy and symptomatic plants is recommended.
How should I sample?
Use a soil probe to collect subsamples (soil cores). The more soil cores collected for each defined sampling area, the better. The best technique is to push the soil probe slightly angled toward the root at a distance of 2 inches (5 cm) from the base of the plant. Pool the cores and mix the soil thoroughly, then send. If soybean is not currently planted in the field, collect soil cores over a defined area.
Samples should be collected from different parts of the field because nematodes are not evenly distributed. A consistent sampling pattern must be applied in order to make meaningful comparison when results are obtained.
Generally, a zigzag pattern is used to collect soil samples, however, other patterns may be applied (see picture below). Collect soil cores equidistant from each other to cover the defined area. A composite sample should represent no more than 20 acres (10 ha) and the area sampled should have similar soil texture and cropping history.
Guidelines for SCN soil sampling
(also see Visual Guidelines for SCN Sampling)
Conveniently, these soil samples can be used for soil fertility analysis. The best data is created when soil samples are collected from areas of the field with similar soil texture.
- A 1 inch (2.5 cm) diameter cylindrical probe can be used to collect soil samples. Soil cores must be collected at depths of 6 – 8 inches (15 – 20 cm).
- Collect 30 to 40 soil cores (subsamples) from 10 – 20 acres (5 – 10 ha) area in a bucket, breaking the soil cores and mixing them well. This will represent a composite sample for the area sampled.
- Place a homogenized composite soil sample (at least 2 cups [500 ml] in volume) in a plastic bag and label it with a permanent marker. Ziploc plastic bags are recommended. Do not use paper bags.
- Protect the soil samples from direct sunlight, overheating in a hot truck to prevent the nematodes from dying.
- Ship samples within a few days of sampling to obtain the best numbers.
What is the best way to label a sample for diagnostic submission?
Most nematology laboratories have a sample submission form, but sometimes these are not available. A soil sample submission will need the following information:
- Name, address, phone number, and/or email
- Location of the field (GPS coordinates if possible)
- Sampling date
- Size of the field that was sampled
- Previous crop history – if possible 2 or 4 years
- Identification number of the field (or plot)
- Application of any pesticide (current or previous year)
In the field, however, plastic bags must be labeled with a waterproof permanent marker. The label should have at least the sample identifier (name, location or code given to the field sampled) and the date sampled. Soil samples with no label are nothing but bags of dirt.
Where can I send my sample for diagnosis?
Nematology Lab at OSU
110 Kottman Hall
2021 Coffey Rd.
Columbus, OH 43210
Spectrum Analytic Inc.
1087 Jamison Rd. NW
Washington Court House, OH 43160
Brookside Laboratories, Inc.
200 White Mountain Dr.
New Bremen, OH 45869
Hand-out Materials Available for Distribution
Download Visual Guidelines to SCN Sampling (PDF).