Update from the Field: Nematodes, the Other Insect
Posted by Dave Dyson, Agronomist on August 08, 2018
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If I had to pick one insect that has the greatest influence on soybean production worldwide year in and year out, I would pick the soybean cyst nematode. These microscopic insects live in the soil and attach to the soybean root, literally sucking the life out of the soybean plant. These insects can reduce root growth, stunt otherwise healthy soybeans, and transmit diseases to healthy plants.
The American Phytopathological Society suggests that soybean cyst nematodes were introduced to North America during the import of soil from Asia in the late 1800s to obtain inoculum of Bradyrhizobium japonicum. This bacteria has a symbiotic relationship with the soybean plant, living on the soybean root and fixing nitrogen that the soybeans needs. Imported soil was distributed among researchers who were working on the improvement of soybean cultivation in the United States. Soil was also shared among growers to obtain nitrogen-fixing inoculum once its utility had been demonstrated. This sharing of soil spread the microscopic insects throughout North America, wherever soybeans were grown.
The conventional wisdom says that to prevent an explosion in soybean cyst nematode population, rotate to a grass crop (corn and/or wheat) for two years. This will work if you can control other host plant species as well. If soybean cyst nematodes have a host to colonize while the soybean crop is not growing in the field, rotating into a grass crop will have no effect on the nematode population. Some of the more common hosts for soybean cyst nematodes are weeds that can be very plentiful in grass crops. Figure 1 shows a chart from the University of Nebraska, outlining which plants are host and which plants will not host this insect.
Figure 1: This table from the University of Nebraska shows which plants will and will not host soybean cyst nematodes.
Planting soybean cyst nematodes-resistant varieties used to be a viable option. Dr. Jamal Faghihi from Purdue University’s Nematology Laboratory has found that resistant soybean varieties are not controlling the population as well as they once did. The new seed treatments from Bayer and Syngenta are your best option for controlling the current population of nematodes. This requires planning and forward thinking to ensure your seed is treated prior to planting.
Testing for soybean cyst nematodes is as easy as pulling a soil fertility test. If we get out and sample in August, we’ll have a good idea where to sample. Sudden death syndrome (figure 2) is a fungal disease that can be spread to the soybean plant by soybean cyst nematodes. This disease usually shows its ugly head later in the season, sometime in August. If we pull our soil samples where we find sudden death syndrome, we will not have to guess where the “hot” pockets of nematode will be.
Figure 2: This image shows sudden death syndrome, a disease that will always present with interveinal chlorosis. This picture was taken near Walton, IN, in 2017.
In conclusion, soybean cyst nematodes will always play some role in soybean production. How much yield they suppress is completely up to the producer. Just as in preventing weed resistance, controlling soybean cyst nematodes should be a four-prong attack:
- Rotate to a grass crop once or twice between soybean crops.
- Control host weeds, even in the winter.
- Plant soybean cyst nematodes-resistant variety soybean seed.
- Treat your soybean seed with a nematicide.
Contact someone from The Andersons’ agronomy team for help in testing and making seed decisions for the 2019 soybean crop.
Dave Dyson is a regional agronomist for The Andersons’ Farm Centers which are located throughout Ohio, Michigan, and Indiana. He is an Indiana native and grew up on a dairy farm in Miami County. A graduate of Purdue University with a degree in Crop & Soil Science, Dave has a deep knowledge of various agronomic topics and is committed to helping growers improve their crops. If you have any questions, Dave can be reached at firstname.lastname@example.org.