Response of Four Summer Annual Weed Species to Mowing Frequency and Height

Greenhouse experiments were conducted in 2011 to evaluate the effect of mowing frequency and mowing height on four summer annual weed species (large crabgrass, barnyardgrass, giant ragweed, and common lambsquarters). Plants were clipped at three heights (5, 10, or 20 cm) and at two frequencies (single clipping or repeated clippings at the same height) to simulate mowing. A nonclipped control was also grown for each species. When clipped once, large crabgrass, barnyardgrass, and giant ragweed produced at least 90 % of the total dry weight (DW) of the nonclipped plants, and common lambsquarters produced at least 75 %. A single cut was generally not sufficient to prevent weed seed production or kill any of the weeds in this study. Repeated clipping reduced large crabgrass, giant ragweed, and common lambsquarters reproductive DW to 46, 27, and 10 % respectively, of the nonclipped control. Barnyardgrass plants that were repeatedly clipped produced between 0 and 8% of the seed DW of nonclipped plants, depending on clipping height. Repeated clipping reduced weed total DW to below 40 % for all species compared to nonclipped plants. Our results suggest that, unless combined with other weed management practices, repeated mowing may be necessary to limit the growth and seed production of these weed species.