Kentucky bluegrass(Poa reptans L.) had been the problematic weed for zoysiagrass(Zoysia japonica Steud.) fairway since it shows dark green color during winter. Two experiments were carried out to determine the best herbicide, proper dosage and application timing to control kentucky bluegrass in dormant zoysiagrass fairway of Korea. To investigated the efficacy and proper dosage, four post emergent herbicides (asulam WG(87.6%), flazasulfuron WP(10%), glyphosate SL(41%) and paquat dichloride SL(24.5%)) were treated with various rates on 5 March 2003. Zoysiagrass green-up were evaluated 30 and 60 days after application for phytotoxic effects of the herbicides. As a result, both glyphosate SL(0.4ml/m2, 0.6ml/m2) and flazasulfuron WP(0.06g/m2) showed approximately 90% of control in Kentucky bluegrass, however, glyphosate (0.6ml/m2) and flazasulfuron WP(0.06g/m2) at 60 DAT(days after treatment) resulted in decreasing of zoysiagrass green-up by over 20%. Therefore, it is suggested that an application of glyphosate SL(0.4ml/m2) may be very effective to control kentucky bluegrass in zoysiagrass with the least phytotoxicity of herbicides. To determine the best application timing, asulam WG(0.5g/m2), flazasulfuron WP(0.04g/m2), glyphosate SL(0.4ml/m2) and paraquat SL(0.4ml/m2) were treated to kentucky bluegrass from 25 February to 15 March 2003 with 10 days intervals. In results, kentucky bluegrass was 90% controlled when glyphosate SL(0.4ml/m2) applied on 5 March 2003 with average soil temperature at 3°C. However, zoysiagrass green-up was substantially reduced in all treatments when the herbicides applied on 15 March 2003 with average soil temperature was over 5°C. Therefore, it is also suggested that application timing to control kentucky bluegrass in dormant zoysiagrass would be better under 5°C of soil temperature to avoid unnecessary injury.

Key words glyphosate; application timing; zoysiagrass; kentucky bluegrass; soil temperature