Submitted to: Communications in Soil Science and Plant Analysis
Publication Type: Peer reviewed journal
Publication Acceptance Date: 9/16/2005
Publication Date: 6/1/2006
Citation: Clay, S., Banken, K., Forcella, F., Ellsbury, M.M., Clay, D.E., Olness, A.E. 2006. Influence of yellow foxtail on corn growth and yield. Communications in Soil Science and Plant Analysis. 37:1421-1435. Interpretive Summary: Knowing the levels of crop yield loss caused by weed competition is important for making weed management decisions. To an extent, some of this knowledge is common sense. For instance, the greater the density of weeds in a crop, the greater the expected percentage of crop yield that is lost to these weeds. However, in reality, the interaction between crops and weeds is more complex than simply the effect of weed density. Both weeds and crops interact with many other aspects of their environment besides one another. We explored the relationship between corn yield and a range of densities of yellow foxtail, which is a common grass weed of the Corn Belt. The study was conducted at sites in South Dakota and Minnesota, each for two years. As expected, we found that competition between corn and yellow foxtail varied between sites and years. The percentage of corn yield lost to weeds was highest when growing seasons were cool (growing degree days less than 2250, base temperature = 50 deg F), yellow foxtail emergence was rapid (greater than 10%) by 15 days after planting, and nitrogen fertility was low. In other words, weeds reduce crop yields more severely during cool than warm growing seasons, and in low rather than high fertility sites. Thus, the value of these results is that they provide a cautionary alarm to growers, co-op managers, crop advisors, and agrichemical industry personnel to ensure that corn fields are scouted thoroughly for weeds and adequate soil nitrogen, especially during cool growing seasons. Recognition of this alarm will lessen the frequency of weed control failures, stabilize crop yields, and increase the efficiency of crop production during poor growing seasons.
Technical Abstract: Field studies investigated the effect of yellow foxtail competition on corn growth and yield at two locations on the western edge of the United States Corn Belt: Brookings, SD, and Morris, MN, in 1995 and 1996. Treatments included four densities of yellow foxtail, a weed-free control and, at Morris, two levels of nitrogen (N) fertility. Yellow foxtail and corn growth parameters were measured at V-6 or V-8, silking, and harvest. As yellow foxtail densities increased, total foxtail biomass increased although tillers per plant and individual plant weight tended to decrease. Corn plant biomass and grain yield were correlated negatively to foxtail biomass and foxtail density. Yield loss differed between years and sites and was correlated negatively with growing degree-days (GDD). Timing of weed emergence also may have been critical to yield loss. Simulation models using maximum/minimum air temperatures and rainfall predicted 40% greater proportion of total foxtail emergence 15 days after planting at sites and years when yield loss was greatest. Nitrogen application resulted in greater corn growth and less yield loss than when N was not applied. Defining a single economic threshold level based on yellow foxtail density is not possible. To reduce risk of yield loss, the most conservative estimate for an economic threshold was three yellow foxtail plants/m**2. However, this value ranged up to 55 plants/m**2 under optimal N and weather conditions.