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The introduction of Roundup Ready Soybeans finally gave growers the tool to easily control many of the weed species that have caused so many problems in the past. The task of field scouting is now much less stressful than it once was. It seems that the only plants that are visible above the soybean canopy are a few stalks of volunteer corn. With the widespread use of glyphosate-tolerant corn followed by glyphosate-tolerant soybeans, control of these volunteers is a problem. This really is not a problem since they are only scattered through the field and never put on any kind of an ear. Insects often clip the silks and feed on the pollen, therefore leaving the soybeans alone. Volunteer corn is not a problem, or is it?

Volunteer corn is on the fast track to becoming the number one weed in soybeans. What is the yield loss from a few volunteer corn plants towering in a soybean field? Research studies have shown that as few as 2.4 corn plants per 100 feet of row can reduce yields by 10 percent. With current yields and prices that could result in an economic loss of $50 an acre.

Unfortunately, the problem goes beyond competition for water and nutrients. Corn rootworm has now found a new source of food and shelter in volunteer corn. Both northern and western corn rootworms have found that volunteer corn roots are a good source of nutrition and a very good place to lay their eggs for the next generation. One of the big problems in controlling this pest is the fact that it is so adaptable. The western variant has adapted to lay its eggs in soybean fields, therefore having corn to feed on next year. Northern corn rootworms have adapted to rotations with extended diapause, where the eggs lay dormant through two winters and one growing season. Therefore, in a corn/soybean rotation the eggs hatch occurs when corn is planted.  

When volunteer corn plants come from rootworm-resistant hybrids, the insecticide Bt is not a full dose.  Unfortunately, when the larvae are exposed to a sub-lethal dose of the insecticide Bt, they can build up resistance. This will ultimately cause rootworm corn to become ineffective in controlling the pest.

In studies conducted from 2007 through 2008 Christian Krupke, Ph.D., entomologist with Purdue University reported that Bt volunteer corn in soybeans can act as larval hosts for rootworms, and beetles can survive to adulthood. Krupke is concerned the situation could allow more corn rootworm larvae to overwinter in soybean fields and it could accelerate the evolution of Bt-resistant rootworm populations.

Glyphosate-resistant volunteer corn can be easily controlled by using a herbicide other than glyphosate.   Most grass herbicides, such as Select Max or Fusilade DX can be tank mixed with glyphosate, therefore eliminating an application. 

LibertyLink Soybeans also offer a solution to this problem. Ignite herbicide will eliminate glyphosate-tolerant volunteer corn, as well as any glyphosate-resistant weeds. There are currently no known weed species that are resistant to Ignite. The Liberty Link system is a great, cost effective solution to this problem.