Clipping Height and Frequency Effects on Japanese Brome Seed Production and Viability

Abstract

Japanese brome (Bromus japonicus Thunb.) is an invasive annual grass that is common in the Great Plains. Grazing or clipping in the spring has been shown to decrease Japanese brome biomass, but the effect on seed viability is not as clearly understood. We tested two clipping height and two clipping frequency combinations against nonclipped controls to determine effects on productivity and seeds of Japanese brome in greenhouse conditions. Pots containing two Japanese brome plants each were the experimental unit, with six per treatment, and the experiment was repeated a second yr. Plants were clipped to a 75-mm or 150-mm stubble height on a 7-d or 14-d interval starting at the boot stage, or no clipping occurred. Brome biomass was reduced 35% by clipping to 150 mm and 54% with clipping to 75 mm. No biomass differences were detected between clipping frequencies at either clipping height. Cumulative seed production was reduced at least 54% by clipping and reductions increased with shorter clipping and greater clipping frequency. At the end of the experiment, clipped plants had 7−310 seeds per pot, compared with a mean of 2 585 seeds per pot for nonclipped. Mean seed weight for all clipped treatments was 73% less than that of nonclipped plants. Only 15 seeds germinated from the 150-mm treatment clipped every 14 d. Plants clipped at 75 mm, regardless of frequency, and plants clipped to 150 mm weekly did not produce any viable seeds. Defoliation, across clipped heights and frequencies, drastically reduced the number and viability of Japanese brome seed. Targeted defoliation by mowing or grazing can contribute to Japanese brome control through seed limitation.