and Jennifer Shike, University of Illinios
Last spring, bands of teenagers were seen brandishing weapons in soybean fields. A few rope wick applicators were re-commissioned into service. This week a field cultivator was actually spotted, not rusting behind the machine shed, but working through a field south of Shelbyville, Ill.
Those who lived through the eras when these practices were used regularly likely recognize the symptoms. We have a volunteer corn problem. You can thank last fall’s challenging harvest for corn in the bean field. Heavily reliance on glyphosate-tolerant systems is another culprit.
Aaron Hager, University of Illinois Extension weed specialist, says there are some mid-season options for chemical control. The first step in selecting an herbicide to control volunteer corn is to determine the type of corn planted in 2009.
“Volunteer corn can be controlled with glyphosate or glufosinate unless it carries the traits conferring resistance to these herbicides,” Hager says. “If volunteer corn in 2010 originated from an herbicide-resistant hybrid planted in 2009, alternatives to glyphosate or glufosinate will be needed.”
Volunteer corn density also determines if additional management options are needed. Previous research shows that volunteer corn, growing in clumps or as individual plants, can reduce soybean yield. The higher the volunteer corn density and the longer the interference duration, the greater the soybean yield loss.
Hager observes that several post-emergence herbicides provide excellent control of volunteer glyphosate- or glufosinate-resistant corn. ACCase-inhibiting herbicides (such as clethodim, quizalofop, fluazifop and sethoxydim) provide broad-spectrum control of grasses and are frequently tank-mixed with glyphosate for control of volunteer glyphosate- or glufosinate-resistant corn. Other post-emergence herbicides that can control or suppress volunteer corn include glufosinate (Ignite), imazaquin (Scepter) or imazamox (Raptor).
“Instead of including a tank-mix partner with glyphosate during the initial post-emergence application, farmers often wait to see if additional volunteer corn emerges before treating,” Hager says. “While it’s understandable, the longer volunteer corn grows with soybean, the greater the likelihood of soybean yield loss. Growers will also have to use higher rates of ACCase-inhibiting herbicides to control larger volunteer corn.”
Volunteer corn in corn is another issue. “Unless hybrid selection this year AND last year allow use of glyphosate or glufosinate to control volunteer corn in corn, the options available are identical to those available to farmers 30 years ago: a row cultivator and a weed hook,” Hager says.
“Problem with the cultivator is that it won’t get the volunteers within the row; problem with the weed hook is finding enough warm bodies to handle the implement.” Hager says he told one farmer earlier this spring that he might need to replant the corn or switch to soybean because the volunteer corn was so thick in a field that had two years of glyphosate-resistant varieties used back to back.