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Crop stress = stalk rot risk


Four corn stems split lengthwise to show stalk rot symptoms.
Figure. Corn stalks split length-wise to reveal stalk rot symptoms. The left-most stalk reveals no symptoms, but for the three stalks to the right, symptoms progress from mild to more severe. Photo: Angie Peltier.

It likely goes without saying for even the least observant among us, that the severe to exceptional drought conditions that have been present in northwest Minnesota for most of the 2021 growing season stressed the corn crop considerably.

Kernels demand sugars. 

Developing corn kernels place a very high demand on the plant for sugars. Stress, like that caused by the 2021 drought, reduces the rate of photosynthesis, thereby reducing the amount of sugars that the plant is able to produce. In addition to the abnormally high temperatures and abnormally low precipitation totals, in 2021 much of the corn crop also suffered from nutrient stress as there was little soil moisture into which soil nutrients could be dissolved and carried into plants through mass flow and evapotranspiration.

Many additional stresses can also reduce the rate of photosynthesis: too much moisture, nutrient imbalances, plant injury (ex.: wind, hail, insects, diseases), excessive plant populations, and even long-periods of cloudy weather.

Stalk rots. 

If the plant is unable to keep up with kernel sugar demand, the plant can begin to redistribute sugars from stalk tissue, predisposing the plant to stalk rotting pathogens. In a typical growing year, corn plants are top-heavy and stalk rots increase the chances that plants lodge due to either gravity or wind and other weather events. While the 2021 corn crop in NW MN was abnormally short, gravity and wind can still cause plants to lodge and the crop will still be less than a joy to harvest.

Pinch or push test. 

To better understand how much stalk rot might be present in a field it is recommend that each field is scouted in one of two ways: by pinching or pushing plants. Regardless of the test, walk each field in a zig-zag pattern, checking 20 random plants from five different spots in the field. For the pinch test, pinch stalks toward the base, below the lowest node, checking for firmness. For the push test, hold your arm out from your body and push the plant to see if the stalk bends or breaks.

With either test, there is a significant lodging potential if 10 to 15% of the plants fail your particular test.

Triaging harvest. 

Pinch or push-testing your fields can help in prioritizing which fields need to be harvested first to avoid having to harvest lodged corn. Specialized reel-systems have been designed to better salvage downed corn but these are rare even in strict corn & soybean country like Illinois, Indiana and Iowa, and the southern half of Minnesota.  General harvest recommendations for downed corn include slowing drive speeds and harvesting against the grain.

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