Eliminating Weed Competition

Weeding Out the Competition
Weed management isn’t as simple as it once was. You could make one pass over the field with a herbicide application and maybe make a second pass later in the season to catch any stragglers and hold weeds back until canopy. 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. Small weeds can no longer be overlooked as though they might not affect the overall crop.

Yields Take a Hit

Take, for example, a 2009-2011 study conducted by University of Minnesota Extension. Once weed height reaches 3 to 4 inches — usually when corn is around the V3-V4 growth stage — the crop loses nearly 12 to 13 bu/A within the first week and 27 to 29 bu/A within the second week.

Weeds also hit soybean yields hard. According to a 2012 study conducted by North Carolina State University and the University of Georgia, soybean yields were reduced by as much as 68 percent due to Palmer amaranth interference at a density of one plant per square foot. Likewise, waterhemp reduced yields by as much as 44 percent in 30-inch rows.

Five Factors

These reductions in yield and grain quality are due largely to the crop competing with weeds over five factors, explained in detail by the University of Illinois Extension:
  1. Light: This is especially critical when weeds grow taller than the crop.
  2. Moisture:  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.
  3. Nutrients: Particularly in coarse-textured soils and soils with low fertility, weeds can exhibit a “luxury consumption” of certain nutrients, such as nitrogen.
  4. Space: 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.
  5. Environmental: 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.


To effectively keep resistance at bay, growers need to incorporate mechanical means and cultural practices, and employ diversified herbicides. The LibertyLink® system provides efficient weed management that enables nonselective and selective herbicide rotation. In the field, this means starting the season with a residual product and using multiple effective modes of action during the year and from year to year. The more diverse the weed management program, the better the stewardship for all available weed control products.

In both conventional and traited corn alike, Capreno® herbicide is the longest-lasting postemergence product available, meaning it helps keep your fields clean until the corn canopies. When tankmixed with glyphosate or Liberty® herbicide and applied to corn with the respective traits, you have even more modes of action in the tank for further weed control.


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