Northwest Minnesota soil tests suggest that SCN is widespread

2013-04-18T15:00:00Z Northwest Minnesota soil tests suggest that SCN is widespreadBy ANDREA JOHNSON Assistant Editor Minnesota Farm Guide
April 18, 2013 3:00 pm  • 

Soybean cyst nematodes have followed soybean production into northwest Minnesota.

The microscopic roundworms have hitchhiked rides on floodwaters and equipment.

Now, northwest Minnesota soybean growers are being asked to manage their fields to minimize egg counts.

A farmer survey – funded by the Minnesota Soybean Research & Promotion Council – found soybean cyst nematodes (SCN) in soil from Wilkin, Clay, Becker, Norman, Mahnomen, Polk, Red Lake, Pennington, Marshall, Kittson and Roseau counties in the fall of 2012.

Larger numbers of SCN were found in soil samples from Wilkin and Clay counties than in counties farther north.

In Polk, Kittson and Roseau counties, only one soil sample in each county included 51-100 SCN per 100 cc’s (about 1/2 cup) per soil. Still, the findings are significant.

Five counties – Polk, Pennington, Marshall, Kittson and Roseau – do not have confirmed SCN.

Additional testing will be conducted in 2013 to determine if the counties do have SCN in their soils.

“Regardless of where you are in northwest Minnesota, there’s a potential to already have SCN. It’s time for everybody to put into practice some type of surveillance effort,” said Phillip Glogoza, University of Minnesota Extension crop specialist, Moorhead.

A team from University of Minnesota Extension oversaw the region-wide SCN survey. Unenthused with maps that simply showed whether or not a county had confirmed SCN, they wanted to find areas and fields within counties where SCN was found.

“We can start looking regionally at how this is starting to shake out,” said Glogoza last July. “What is the incidence or percent of fields that we are finding with SCN present? Where are they, and what is the severity? Are we talking 100 eggs per 100 cc, or 30,000 eggs per 100 cc of soil? We haven’t discovered that yet.”

During August 2012 field days and variety plot tours, Extension staff handed out over 1,000 free soil sample kits. Growers sent 330 soil samples, from 211 sites, to the Minnesota Valley Testing Lab of New Ulm.

Participating farmers and landowners received their results directly from the lab.

Extension received SCN counts identified by geospatial reference points. About a quarter – 28 percent – of the samples contained SCN, while 72 percent did not contain SCN, said Glogoza.

The egg counts ranged from less than 100 to 39,000 eggs/100 cc of soil.

“There are growers, field men and distributors who have not seen SCN before in the field,” he said. “It’s time they learn to recognize it.”

Soybean cyst nematode remains Minnesota’s number one soybean pest, and can cause 30-40 percent yield loss.

Glogoza reminds growers that if they see yellow or stunted soybeans this spring, check for female bodies on soybean roots at four or five weeks after planting.

The adult female is lemon shaped, and when fully developed, the body protrudes outside the soybean root and is visible without magnification.

Growers can quickly learn to distinguish the small female bodies from large bacterial nodules.

It’s also possible to see the dark brown cyst of the dead female that houses SCN eggs. The cyst is what is collected when soil samples are processed. Viable eggs within a cyst can survive many years.

The goal of any SCN management program, is keeping egg counts low.

“What we have seen as SCN moves into the region, growers discover it because of unexpectedly low soybean yields,” Glogoza said. “When that happens, that’s when you see high numbers – 30,000-40,000 or more per 100 cc of soil.

“If you are dealing with numbers in that 30,000 range, you put in a resistant soybean and the SCN will overwhelm the resistance. If you allow those high numbers, you’re looking at a longer rotation time away from soybeans, just to get numbers down where you can successfully use SCN resistant varieties.”

University of Minnesota Extension recommendations note that counts of 12,000 SCN per 100 cc of soil are considered in the “high” infestation category. At this population level, growers need to plant non-host crops, such as corn, wheat or alfalfa, for several years to decrease the SCN populations.

When populations reach less than 12,000, growers can begin a five year rotation including: year one – SCN-resistant soybean; year two – nonhost crop; year three – SCN-resistant soybean; year four – nonhost crop; and year five – SCN-resistant variety different than used in year one and three or a susceptible soybean variety if numbers are low enough.

Glogoza suggested that growers could take soil samples to check for SCN as soon as the soil thaws this spring, if they are suspicious. At the end of July or early August, growers can also begin digging and looking for the presence of cysts.

“If you see them, it tells you that you need to sample,” he said. “If you don’t see them, you may still want to sample.

“It’s your job, as a farmer, steward and good manager, to find SCN before they cause problems.”

Copyright 2015 Minnesota Farm Guide. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.

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