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Extension > Agriculture > Crops > Soybean > Soybean cyst nematode management guide > How often, when, and how should I take soil samples for soybean cyst nematode counts to help make management decisions?

How often, when, and how should I take soil samples for soybean cyst nematode counts to help make management decisions?

Fields infested with SCN should be managed to minimize yield loss. In order to manage SCN populations effectively, it is important to monitor SCN populations over time. Distributions of SCN are generally uneven in most fields, and nematode egg numbers can vary with sampling technique. So, to minimize the variability for a representative SCN egg count, it is very important to use recommended sampling procedures:

Fig. 9. Zigzag sampling pattern in a field.

Fig. 9. Zigzag sampling pattern in a field.

There are a number of factors that contribute to the variability of egg numbers from soil samples. SCN eggs are deposited in a cluster, and the spatial distribution of SCN in many fields is an aggregated pattern. In some fields, soil cores may contain high egg numbers from hot spots and low, even zero, egg numbers from non-infested or recently infested areas.

Increasing the number of soil cores collected in each 10-acre area or reducing the size of the area for each sample can increase the precision of the sample. If the hot spots in the field cannot be managed separately from the rest of the field, the best option is to manage the entire field according to the higher population density.

The efficiency of extracting SCN from the soil is dependent on soil characteristics such as texture and moisture content at the time of sampling. Some variability may be associated with the actual laboratory processing of the sample, leading to a rough estimate of the average SCN population rather than an exact measure. However, an effective management program can be implemented using the rough estimate of the average SCN population in a field.

There are other reasons why SCN population densities may vary in two soil samples taken from the same field. SCN egg counts will be highest if samples are collected in the soybean row at the end of the growing season. Due to the variability, it is difficult to compare SCN samples taken from a field at different areas and times of the year.

Long-term SCN management based on soil samples is best done with a sampling plan that is consistent in area(s) sampled, crop sampled, and time of year samples are taken. Since SCN egg population densities are reduced during a year when a nonhost crop is grown, SCN egg counts from samples taken after corn harvest, but before soybean planting, are the most useful in estimating potential soybean yield loss. Sampling in the fall rather than spring allows more time for the soybean producer to develop an appropriate SCN management plan.

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