Blast of wind cuts a swath through Midwest
It’s official—a derecho descended upon the Corn Belt last week.
Straight line winds exceeding 100 mph tore through the center of Iowa and continued into northern Illinois and Wisconsin on July 11. I saw some of the aftermath of the event near Dixon, Ill. It wasn’t pretty.
Green snap, where the corn stalks break at the node, was evident in some fields. However, I saw more root lodging, where the plants lean at different angles as the roots pulled partway from the soil.
Extension agronomists and plant pathologists in Iowa and Illinois have been quick to reach out to growers in impacted areas. Roger Elmore, Iowa State agronomist, notes in his reports that the damage was all the more gut-wrenching because the Iowa crop was in prime condition prior to the wind. However, he also notes that soils were wet at the time—thus, there was more root lodging than green snap.
According to Elmore, root mass reaches its maximum at silking (R1). This spring’s delayed planting and the resulting delayed crop progress might actually help in the stricken areas. Plants root lodged before the silking and blister stages (R1/R2 ) are somewhat able to compensate for the canopy disruption caused by lodging.
In the area I visited, impacted corn plants were already trying to stretch upward and resume a vertical growth pattern.
Emerson Nafziger, University of Illinois extension agronomist, says the two major types of injury suffered by "leaning" plants are disruption of the root system and disorientation of the leaves. Root systems often lose more than half of their contact with the soil, and this reduces their ability to take up water and nutrients. Having some of the leaf area underneath the plants and, in extreme cases, down against the ground, reduces the amount of sunlight these leaves can take in.
Unfortunately, this is happening at a time when plants need to have maximum photosynthetic rates to assure successful pollination. One positive is that this slows the rate of water uptake, and this may help roots to reestablish soil contact, both by soil settling (with rainfall) around the roots, and by some new root growth, Nafziger says. The closer to pollination this happens, the less ability plants have to regrow roots, but this ability doesn’t go away until several weeks past pollination.
"One of the keys to recovery of root-lodged plants is the degree to which the lower stalk can turn back upwards, bending so that the leaves can be reoriented better to intercept sunlight," Nafziger says. "The later in growth the lodging happens, the less flexibility stalks have to do this and the higher up the stem this flexibility exists. Such plants end up ‘goose-necked’, but that by itself doesn’t cause a lot of harm if the leaves can intercept the sunlight and the roots can recover well enough."
Research that has been done in which plants are artificially root-lodged at different times and to different degrees has generally shown some yield loss. But this loss has not been as great as the appearance of the crop immediately after the event might suggest, Nafziger adds.
Flattened corn may provide a better microclimate for disease development though. Alison Robertson, Iowa State plant pathologist, reviews the pros and cons of spraying downed corn with a fungicide.
University of Wisconsin agronomist Joe Lauer urges growers with fields in the wind-damaged areas to be patient and let the corn crop recover. Make notes about hybrid differences for lodging resistance, crop development and whether brace roots had formed. Watch lodged fields closely, especially later near harvest. He says growers should expect harvest to be more difficult.
Jennifer Shike contributed to this article.