Weed management isn’t as simple as it once was. While herbicide resistance seems to get most of the attention as one of the biggest weed management challenges, it’s just one factor that is making weeds tougher to control.
Consider that a single velvetleaf seed can remain viable in soil for up to 50 years and the likes of waterhemp or Palmer amaranth can produce hundreds of thousands of seeds – per plant. Even a few weed escapes can no longer be overlooked under the assumption that they might not affect the overall crop.
Yields Take a Hit
Take, for example, a 2009 to 2011 study conducted by University of Minnesota Extension1. Once weed height reaches 3 to 4 inches – usually when corn is around the V3-V4 growth stage – if the weeds are not removed, the corn crop loses nearly 12 to 13 bu/A in the first week and 27 to 29 bu/A within the second week.
Five Weed Competition Factors to Consider
These yield reductions are due largely to the crop competing with weeds over five factors, explained in detail by the University of Illinois Extension2:
This is especially critical when weeds grow taller than the crop.
After removing a dense population of weeds, the amount of water a crop can access is an essential factor in how well the crop recovers.
Weeds consume nutrients that otherwise could be used by the crop such as Nitrogen, particularly in coarse-textured soils and soils with low fertility.
Dense infestations of weeds lead to allelopathy – the suppression of plant growth due to release of natural plant-derived substances – which contributes to yield loss due to additional competition.
More than any other factors, soil and air temperature, and soil moisture and rainfall before, during and after initiation of competition affect weed emergence and growth, herbicide effectiveness, the competitive interaction between crop and weed, and the ability of the crop to recover from early weed competition once weeds have been removed.
Bayer Solutions for Weed Control
One of the most effective ways to control weeds is to stop them before they have a chance to emerge. Products such as Corvus® herbicide can be applied before your corn is in the ground and any weeds have had a chance to emerge for effective burndown control. Corvus can even be applied through the V2 corn growth stage, when the weeds that might emerge are still posing minimal competition. Corvus has two effective and complementary modes of action for weed control and uses the power of reactivation throughout the season with just a half-inch of rain.
Corvus can be tankmixed with atrazine, the preferred tankmix partner with Corvus, as the two herbicides work together to enhance weed control beyond what the two components offer individually. Corvus contains a proprietary safener, which enables plants to better withstand herbicidal activity. The safener imparts additional protection and reduces symptoms from certain herbicides used in a tankmix or used post-emergence in the early stages of corn growth.
Depending on the weed pressure and spectrum, a second pass of DiFlexx® DUO herbicide is recommended as a zero-tolerance approach to weed control. DiFlexx DUO provides powerful postemergence control against the full range of tough weeds, especially glyphosate-resistant ones. This approach will help keep competition at a minimum through the corn canopy and also help reduce the weed seed bank for the following season.