Changes in the weed species composition of the southern United States: 1974 to 1995

The Southern Weed Science Society has conducted an annual survey of the most troublesome weeds in several major crops since 1971. The objective of this summary was to characterize shifts in weed populations over a 22-yr period in four major agronomic crops. For corn, soybean, cotton, and peanut, the largest increases in rank as the most troublesome weeds were found with sicklepod and bermudagrass. The largest decreases were found with johnsongrass, crab-grasses, and common cocklebur. Morningglories and nutsedges remained relatively constant weed problems over the 22-yr period. Sicklepod, nutsedges, and morningglories were the three most troublesome weeds averaged over all crops because they are so well established and relatively difficult to control. Pigweeds (Palmer amaranth, sandhills amaranth, tumble pigweed, and waterhemps) have become increasingly important in soybean, peanut, and cotton in a limited number of states.