Final opportunity to scout for soybean cyst nematodes and sudden death syndrome

Soybean harvest can be a valuable, final opportunity to identify soybean cyst nematodes and sudden death syndrome in drought-damaged fields, and better prepare yourself for next season.

The summer of 2012 was one that many producers would just as soon forget. With extreme drought and spider mite infestations that were the worst in memory throughout much of Michigan, it would be hard not to want to put the season in the rearview mirror of the combine and move on to fall tillage. But if you are willing to invest a little more time into the harvest period, it could provide some better insights into what may have caused additional yield losses and ways that you could manage these problems in future years.

The process starts by looking for anomalies in plant stands and yields that don’t seem to “fit the pattern.” This is easier to evaluate during the growing season, but even if you didn’t, poor stands and yields can still identify areas that may pose future challenges. In fields I have walked this summer, lower portions of the fields received enough runoff water to provide areas of ample growth and higher yield potential. If you are seeing irregular patches in these areas that exhibit stunted growth or have sparse stands, drought was probably not the only problem.

There are several potential causes for poor plant growth. Spider mite damage in soybeans is sort of an unusual event that was very prevalent this year. Pockets of spider mite damage pretty much occurred across wide areas of fields in 2012. However, spider mites are not the only possibility. Soybean cyst nematodes can also cause severe stunting and stand and yield losses.

Sudden death syndrome is also another possibility. Look at the plants near the margins of the affected areas to see if the petioles are still attached to the plants. This is often an indicator that sudden death syndrome was the culprit. If the petioles dropped off, the damage may have been caused by soybean cyst nematode damage alone.

There’s no better time to sample for soybean cyst nematodes than right after harvest, before tillage is completed. Collect samples through the remaining root mass and submit them for testing. We have been seeing a soybean cyst nematode biotype shift in some of our research plots near Decatur, Mich., which is showing that the PI88788 source of soybean cyst nematode resistance (the most common source in soybean varieties) is not as effective in controlling the pest as it was in the past.

Be aware that deer feeding was also intensified by the dry conditions of 2012. Areas that suffered browse injury early often show signs of heavy branching and low, dense pod set.

Evaluating areas of poor stand and yield performance can help you to identify what caused the problems and improve management in future years. If you suspect soybean cyst nematode or sudden death syndrome issues, you can select varieties that exhibit partial resistance to sudden death syndrome or select a different source of soybean cyst nematode resistance to manage these pests.

One last thing to consider is the density of winter annual weeds in the fields that you are harvesting. Purple deadnettle, chickweed and henbit may not look to be a serious threat in the fall, but if you have enough plants in the field, they can lead to a thick mat of green as you approach planting time next spring. Purple deadnettle and Henbit are alternate hosts for soybean cyst nematodes. Many white grub species, including Asiatic garden beetle and Japanese beetles, can feed on winter annual roots in early spring.

With the early harvest season and expected warm conditions this fall, a quick pass with a fall-applied herbicide or fall tillage can help to reduce challenges next spring.

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