Competition of Smooth Pigweed with Corn and Soybeans

Yield reductions from the heaviest stand of smooth pigweed (Amaranthus hybridus L.) averaged 39% for corn and 55% for soybeans. For corn the increase in pigweed dry matter about equalled the decrease in the dry matter from the crop; the total dry matter yield was relatively constant. Pigweed grew taller than soybeans, and the dry weight of crop plus pigweeds was 1 1/3 times that of weed-free soybeans. As stand of pigweed was increased, there was a decrease in yield of grain, cobs and stalks or straw, diameter of cornstalks, height of crop, and soybean pods per plant. Yield reductions obtained emphasize the importance of both chemical and cultural measures for reducing competition between row crops and weeds.