Foregoing field tests could spell nematode troubles for soybean crop

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COLUMBUS – Soybean growers who failed to sample their fields last fall for soybean cyst nematode may be in for a surprise this growing season.

Mac Riedel, an Ohio State University plant pathologist, said that snow cover and relatively mild winter temperatures may have aided in survival resulting in high pest populations this spring.

Those populations could spell trouble, especially for growers who rushed to plant early and may not have tested their fields for egg counts beforehand.

Planting early. “Growers have been planting very early this season,” said Riedel.

“If those growers didn’t test their fields in the fall, I’m wondering what kind impact that’s going to have on their crop.”

According to the Ohio Agricultural Statistics Service, 46 percent of the soybean crop is in the ground, 24 days ahead of last year’s scheduled. Nine percent of that crop has already emerged.

“If we have a spring with little rain and high soil temperatures, we could see a rapid development of nematodes. We may run into some problems in some fields,” said Riedel.

“If SCN is present, growers will start to see chlorotic plants in mid-June to early July.”

Damages crop. Soybean cyst nematodes feed on the roots of young plants, which prevents the roots from taking up vital nutrients. The result is a drop in yields and economic losses.

The best management tool to control nematode populations is to sample fields with a history of problems and rotate resistant varieties based on relative egg counts.

Yield loss threshold begins at 200 eggs per cup of soil.

At 2,000 eggs per cup of soil, most susceptible soybean varieties suffer significant economic losses.

At 5,000 eggs per cup of soil, growers should avoid growing soybean varieties altogether, even resistant varieties.

“With susceptible varieties, when there is stress on the crop or poor nutrition, you can detect economic losses under 1,000 eggs per cup of soil.

“So at the 10,000 range, susceptible beans are producing very little yield and resistant beans will probably have root damage and won’t yield optimally,” said Riedel.

Economics. Additionally, since populations tend to increase tenfold on host crops, planting another soybean crop next spring into a field with 20,000 eggs per cup of soil is likely to increase populations to 200,000 eggs per cup of soil-forcing the grower to plant non-host crops for five to six years to bring populations below economic threshold.

“That outlook is obviously not economically viable for a grower. So it’s important to get out there and test fields to determine what populations you do have,” said Riedel.

He noted production numbers in some fields during the late 1980s and early 1990s showed only a 6-8 bushel per acre harvest in fields with nematode populations of 200,000 eggs per cup of soil or more.

One shot. One thing that is going for growers so far that may help keep populations in check is recent rains and cool soil temperatures.

“Soybean cyst nematodes don’t develop too well in wet soils, and low temperatures, below 65 degrees, tend to suspend nematode activity,” said Riedel.

“Such conditions may allow early-planted soybeans to develop roots and start growing before SCN has a chance to pile on.”

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