Effect of Time of Giant Foxtail Removal from Corn and Soybeans

With a corn (Zea mays L.) yield of 144 bu/A on weed-free plots, giant foxtail (Setaria faberii Herrm.) reduced corn yields 1, 2, 5, 7, and 18 bu/A, respectively, when removed when 3, 6, 9, and 12 inches high and at maturity. With a soybean (Glycine max L.) yield of 30 bu/A on weed-free plots, the same treatments reduced soybean yields 0, 0, 1, 2, and 18 bu/A, respectively. Giant foxtail competing with corn delayed tassel emergence but had little effect on moisture of grain or on shelling percent at harvest. The total dry matter produced per acre remained relatively constant whether the dry matter was made up of corn alone or corn and weeds. The greatest competitive effect of giant foxtail with soybeans occurred after the reproductive stage of soybeans began or after the weeds became sufficiently dense to reduce the light which soybeans received. Early-season competition had greater effect on corn than on soybeans. However, the taller growing corn competed better than soybeans with giant foxtail later in the season.