Volunteer corn pressure in soybean fields changes from year to year but the need to control these troublesome weeds should be standard operating procedure for growers in Eastern Canada.

Throughout a difficult 2018 harvest across Ontario, growers battled an epidemic of Gibberella ear rot in corn, resulting in unprecedented DON levels. To help manage the problem, combine settings were adjusted at harvest to help blow out diseased kernels. In some cases, fields were simply combined with the kernels being blown onto the ground.

With all those corn kernels set to germinate last spring, growers were on high alert to actively manage volunteer corn in their 2019 soybeans, says Syngenta territory sales representative Brad Garlough. He stresses that it’s vitally important that growers control these volunteers in IP soybean crops: “If there are kernels in your sample, you could lose the premium and opportunities in the export market.”

Start with a strong pre-emerge program

Most growers combined a strong pre-emerge herbicde program with second herbicide application to target the first flush of volunteer corn at the 1st and 2nd trifoliate stage of soybean development (V1 – V2), when soybeans are most vulnerable to yield loss. “A lot of people did a great job,” says Garlough. He adds that some growers did require a second in-crop application. “That’s what happens when you get a rain a little later on and you get a second flush of volunteer corn.”

Garlough’s territory includes Perth, Wellington and Waterloo counties, a hub of IP soybean production in Ontario. “Growers should always be paying attention to volunteer corn because it could make or break a premium. Proactive growers work hard to make sure volunteer corn doesn’t make an appearance.”

This year also brings some new concerns for growers looking to manage volunteers. Garlough notes that difficult harvest conditions last fall meant many acres of corn were left standing through the winter and were harvested this spring. “A lot of cobs fall during the winter and more are knocked down by animals during the winter. If you leave corn standing through the winter, you should put down a volunteer corn control product in your soybeans,” he adds.

Tidy up volunteers

It pays to tackle volunteer corn in both IP and Roundup® Ready soybeans, notes retired Syngenta Canada agronomic sales representative Steve Johns. He explains that research from South Dakota State University shows that volunteer corn density of 5,000 plants/acre can reduce soybean yields by 20% — that’s a 12 bu/ac yield loss in 60 bu/ac soybeans. Yield damage can be even more extensive in parts of a field where high numbers of dropped ears produce clumps of volunteer corn.

Johns reminds growers that volunteer corn is one of their soybean crop’s most competitive weeds. Generally, he believes growers spray volunteer corn too late. They tend to feel that more corn plants will emerge and wait for an opportunity to kill them all. “But it’s that first flush that will do the most yield damage,” he says.

Whether it be Roundup Ready 2 Xtend® or IP soybeans, growers do have herbicide control options like Venture® L, notes Garlough. Venture L is considered one of the most active products on volunteer corn and low rates will help tidy up volunteers economically. With a 90-day harvest interval for use on soybeans (75 days on edibles) growers can still spray Venture® L in early July, he notes. It’s always a good idea to check with your elevator on your volunteer corn herbicide choice on your IP soybeans before application. 

The trouble with tillage

Garlough says growers also need to be mindful of the impact pre-plant tillage in soybeans can have on managing volunteers. Recent Ontario Ministry of Agriculture, Food and Rural Affairs research indicates that growers can expect plant stands to be 10 percent higher and fields to yield an extra two bushels per acre at harvest when they till before planting. It also warms and levels the seedbed.

That’s enticing for growers, but it can cause headaches for volunteer management. In many cases, that spring tillage can effectively plant corn seed laying on the ground. “It’s much harder for that corn to establish if you don’t do tillage. In the case of volunteer corn management, no-till certainly has an advantage,” says Garlough.

Good resistance management strategy

Controlling volunteer corn is also a good resistance management strategy, especially when it comes to corn rootworm. Garlough points out that volunteer corn does not express the same level of Bt toxin for corn rootworm control as hybrid seed corn. That means volunteer corn can provide a bridge for rootworm to survive a soybean crop and pose resistance concerns for the following corn crop.

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