Knock on wood: Southern Minn. corn, beans look good

Southern Minnesota corn and soybeans are looking good, heading toward physiological maturity, benefiting from timely planting, timely rains. The region escaped a widespread derecho wind storm an hour or two to the south in Iowa.

SHERBURN, Minn. — Farmers in south-central and southwest Minnesota are likely to meet or exceed their yield targets for corn and soybean this year, according to one of the region’s leading crop watchers.

Lizabeth Stahl, University of Minnesota regional Extension educator in crops, has special responsibility for 14 counties but has a statewide role in weed issues, cover crops and private pesticide applicator certification.

Lizabeth Stahl, a University of Minnesota Extension educator for corn and soybeans, checks out crops on the Bill and Kaye Truesdell farm near Sherburn, Minn., in Martin County. Photo taken near Sherburn, Minn., in Martin County, Aug. 24, 2020 Mikkel Pates / Agweek

Stahl said her "armchair calculations" show yields in the 210- to 220-bushels per acre range in one corn field she looked at in the Sherburn area of Martin County. Many of the soybean fields will hit the 60-bushel averages that growers seek.

The region had a good planting season, followed by adequate moisture, particularly during corn pollination. Some areas got excessive shots of 4- to 6-inch rain. The moisture is ahead of average for the season, but there had been relatively little in August.


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Lizabeth Stahl, University of Minnesota regional Extension educator in crops, expects the crop in the Sherburn, Minn., area will reach physiological maturity by mid- to late-September. (Mikkel Pates / Agweek)

“We're working off that (subsoil) moisture right now. We could use a little more,” she said on Aug. 24. “You can see some stress."

Some farmers in the 14 counties she's most familiar with caught some strong wind storms, and spots of hail, but they escaped the brunt of the derecho straight-line wind storm that hit crops an hour or two to the south in Iowa.

One trend is that more farmers are looking harder at “conventional” corn hybrids, Stahl said. "A lot of people are planting Bt (expressing one or more proteins from the bacterium (Bacillus thuringiensis) hybrids,” she said. “But with economics the way they are right now, people are trying to see where they can cut costs."

Stahl pulled a representative cob from a field end row. The ear was filled out, pretty much to the tip. This indicates pollination was very successful, which can help optimize yields. It also indicates the farmer might have increased population a bit.

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The condition of corn cobs in the Sherburn, Minn., indicate pollination was successful. (Mikkel Pates / Agweek)

When breaking the cob, she noted it was about three-quarter “milk line” — the boundary between milky and solid (starchy) areas in the kernel — close to maximizing the dry matter accumulation.

"We want to extend the … grain-fill period as much as possible," she said. "We do have some warm temperatures in the forecast so that's going to speed things along." Based on computer models for growing-degree days in corn, Stahl expects the crop in this area will reach physiological maturity by mid- to late-September.


"We should really minimize the need to dry down corn artificially. We may get by, hopefully, with natural air drying. It's really going to help us with economics, cutting out that drying cost," Stahl said.

Soybeans on Aug. 24 were in the R5" (filling seeds) to the "R6" (reproductive) stage where the pods are full and maturing.

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Lizabeth Stahl, University of Minnesota regional Extension educator in crops. (Mikkel Pates / Agweek)

One trend is that more farmers are trying out the "narrow" rows — 7.5 to 15 inches widths — compared to a more traditional 30-inch spacing. Stahl says there is a trade-off with potential issues of white mold disease, which is more related to high population.

Stahl says farmers need to use a planter with good seed placement to make narrow rows work best.

Stahl judges field potential based on disease threats, including sudden death syndrome and soybean cyst nematode.

"If we’ve had decent moisture, low-stress: all of those things really play a big role in your yield potential," she said.

It's been a relatively low-stress year for soybean aphids. Yields will vary based on whether fields were sprayed when needed, and how effective the treatment was.


Stahl noted that Bruce Potter, a University of Minnesota integrated pest management specialist, is leading a region-wide watch for soybean gall midge — a newer pest first discovered in the region in 2018.

“A few more counties in 2019 and we’re still finding that in 2020," she said.

The University of Minnesota publishes variety recommendations for southern-, middle- and northern-Minnesota farmers, based on research results from multiple locations, with all of the major companies.

Producers should watch for plants affected by "sudden death syndrome." Leaf veins remain green, but brown "necrotic tissue" is taking over the interveinal area. A similar disease is brown stem rot. Farmers can send in questions to the University of Minnesota Plant Disease Clinic for a diagnosis, to help in variety selection and seed treatment decisions in future years.

Mikkel Pates is an agricultural journalist, creating print, online and television stories for Agweek magazine and Agweek TV.
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