Saturday, December 4, 2021

Detect nematode woes in soybeans with fall soil sampling

• By Ed Sikora •

root-knot nematode damage
Figure 1: Root-knot nematode damage on a soybean root — photo courtesy Alabama Cooperative Extension

Soybeans in Alabama can be damaged by various nematodes with root-knot (Fig. 1), soybean cyst and reniform nematodes the most common culprits. Soil samples are the best way to correctly determine if plant-parasitic nematodes are present in a field.

The optimum time to sample soybeans for nematodes is in September or October as the crop matures. This is when nematode populations should be peaking so they are easy to detect and will tell growers what they will face the following growing season.

The worst time to sample for nematodes is in late winter through early spring as nematode population levels are at their lowest and may not be detectable.

Diagnostic or preventative

nematode damage
Figure 2: Some of the first visual symptoms of nematode damage are plant stunting and yellowing — photo courtesy Alabama Cooperative Extension

Nematode soil samples can be diagnostic or preventative. Diagnostic samples focus on portions of the field where plants look stunted (Fig. 2) or abnormally yellow during the season indicating a potential problem area.

Diagnostic samples should consist of soil samples from the edge of the affected area as well as a second sample from a relatively normal part of the field for purposes of comparison.

Preventative samples are for fields where the grower is interested in knowing what potential problems await, especially when considering new land to farm. Preventative sampling consists of collecting random samples from the whole field. Growers can divide the field into 5- to 10-acre sections and collect 15-20 random samples of soil from each section by following a “zigzag” pattern across the field.

Soil samples should be collected from the top 6 to 8 inches of soil using a soil probe or shovel with samples taken directly from the root zone if plants are still present. Mix samples thoroughly and remove 1 pint of soil for the laboratory analysis.

Place soil in a zip-lock bag and avoid exposing samples to excessive heat or freezing conditions, and don’t let samples dry out. Store samples in a cool area until shipment can be made to the diagnostic laboratory.

Recordkeeping

Keep written records of the number and origin of each sample. For us to make a useful recommendation, the following information must be given: (a) previous crop history and (b) crop to be planted. This information, along with the name and address where lab results are to be mailed, can be placed on the “Information Sheet for Nematode Soil Samples” (Form ANR-F7), available at Alabama Cooperative Extension offices.

Mail samples to the Plant Diagnostic Laboratory, 961 S. Donahue Dr., Auburn University, AL 36849-5624. The service charge for nematode soil testing is $10, but we are currently running free nematode soil samples for soybean growers in Alabama.

Support for the free service comes from funding from the Soybean Cyst Nematode Coalition and the Alabama Cooperative Extension System. This is for nematode testing only, and we will only accept samples that are collected from current soybean fields and/or fields that were in soybeans last year or will be going into soybeans in 2022.

We would accept a maximum of three samples per farm as we have limited funds for this service.

Dr. Ed Sikora is an Auburn university Extension specialist and professor of entomology and plant pathology. He may be reached at Auburn University.

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