Abstract: Warm-season lawns are vulnerable to Imperata koenigii invasion in summer in subtropical regions. The purpose of this study was to determine the effects of mowing frequency on the competitiveness, plant growth, and quality of a Zoysia tenuifolia lawn invaded by I. koenigii to varying degrees. We established an experiment in which Z. tenuifolia lawn was artificially planted with I. koenigii at five different proportions (10%, 20%, 30%, 40%, 50%) and mowed at four different frequencies (0-3 times per month) to a stubble height of 7 cm for 3 consecutive months. Competitive parameters such as relative yield, total relative yield, attack power, and competitive balance index were determined for both plants. Growth parameters including plant height, number of tillers, number of leaves, biomass, and root-shoot ratio were also analyzed. The quality of the lawn was evaluated comprehensively by calculating indexes of density, texture, leaf color, and uniformity, and by determining grass height and biomass. The results showed that: 1) The mowing frequency significantly affected the aboveground and underground competition parameters of Z. tenuifolia and I. koenigii (P<0.05). Mowing increased the antagonistic effect of the aboveground parts between the two plants, while the antagonistic effect of the underground parts between the two plants was reduced by mowing 2-3 times per month. 2) Mowing frequency and the proportion of I. koenigii had stronger effects on the aboveground parts of Z. tenuifolia than on its underground parts. Mowing once per month improved the aboveground competitiveness of Z. tenuifolia, while mowing twice per month improved its underground competitiveness. The synergistic effect of mowing frequency and increased proportions of I. koenigii increased its attacking power against the Z. tenuifolia root system. 3) The mowing frequency and proportion of invasion significantly affected the growth of I. koenigii and Z. tenuifolia. Mowing 1-2 times per month increased the tiller number and leaf number of both plants. Mowing twice per month increased the tiller number and leaf number of Z. tenuifolia increased by about 40%. The biomass of Z. tenuifolia decreased when the proportion of I. koenigii was 10% or more, and the tiller number of Z. tenuifolia decreased when the proportion of I. koenigii was 20% or more. When the proportion of I. koenigii was 30% or more, the plant height of Z. tenuifolia increased but its leaf number decreased. Mowing frequency was the main factor affecting the plant height, tiller number, leaf number, and root-shoot ratio of Z. tenuifolia. The proportion of I. koenigii mainly affected the biomass of single Z. tenuifolia plants. 4) Mowing frequency mainly affected the density, height, and biomass of the lawn, but the proportion of I. koenigii mainly affected the texture, leaf color, and uniformity of the lawn (P<0.05). The best combination in terms of the comprehensive quality of the lawn was 10% or less I. koenigii and mowing twice per month. The lawn quality was mainly affected by the mowing frequency, followed by the proportion of I. koenigii. 5) Mowing 1-2 times·month^-1 significantly increased the aboveground and underground competitiveness of Z. tenuifolia against invading I. koenigii, and promoted tiller formation in Z. tenuifolia, reduced lawn height, and improved the density and texture of the lawn. However, mowing could not change the fact that the aboveground and underground competitiveness of Z. tenuifolia lower than that of I. koenigii. Therefore, the basic requirements for maintaining the quality of a Z. tenuifolia lawn in summer are to control the proportion of I. koenigii at 10% or less and mow twice per month.

Key words: Zoysia tenuifolia, Imperata koenigii, attack, competitiveness, mowing frequency, lawn quality