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Sort through soybean disease symptoms

Soybean Watch: Slideshow outlines how to identify sudden death syndrome.

The Soybean Watch ’19 field consists of two varieties from two different seed companies, both no-tilled into cornstalks with a John Deere 750 drill on June 12. “The planting date is important because if they had been planted two days later, on June 14, it’s quite possible they would have needed replanting,” says Steve Gauck, a Beck’s sales agronomist based near Greensburg, Ind. Beck’s sponsors Soybean Watch ’19.

Ten continuous days of rain and a sudden cool snap, which began June 15 where this field is located, prevented many fields of both corn and soybeans that were planted June 14 from germinating, emerging and establishing themselves properly. The two-day head start helped this field make it.

The two varieties share one thing in common: seed was treated with Ilevo. One variety was also treated with a full fungicide and insecticide package. The stand in that variety is estimated to be about 15,000 to 20,000 plants per acre higher, although both are above 100,000 in most areas of the field.

The Ilevo was added to protect against sudden death syndrome. Some areas of the field can be wet, and the farmer didn’t know when he would be planting when he ordered seed. “It still likely paid off,” Gauck says. “Those cool, wet conditions favor SDS infection, which occurs early. It just happened to occur in mid-June instead of mid-April or mid-May this year.”

Check for diseases

When Gauck visited the field in mid-September, he found an isolated plant or two in each variety showing symptoms of SDS. “[Ilevo is] not bulletproof,” he says. “You may still see some SDS. But you won’t see what you would have seen without using it.”

To identify SDS, Gauck first looks for interveinal chlorosis, or yellowing, and necrosis, or dead tissue, on upper leaves. To confirm, he pulls a plant and splits it open. If the pith is white and not brown, it eliminates brown stem rot. “You can usually find small watermarks inside the stem if the infection is caused by SDS,” he says.

Gauck also saw a few leaves with one or more frogeye leaf spot lesions, and several yellowish leaves, which he suspects may be related to bacterial disease. “You might suspect SDS at first, but upon closer examination, the symptoms didn’t quite match up.

“Leaves very low in the canopy were yellow because they just weren’t getting enough sunlight,” he adds. “It’s also the time of the year when some leaves may begin to turn naturally, although these plants still had a long way to go before reaching full maturity. It can make scouting more difficult.”

Gauck has even seen white mold in plots in southern Indiana this year, something he hardly ever sees. White mold is typically more common in northern Indiana, and there haven’t been widespread reports this season. However, another agronomist identified white mold in a field in Shelby County. No white mold was found in the Soybean Watch ’19 field.

Check out the slideshow to see photos of these diseases.

TAGS: Crop Disease
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