Calepitrimerus vitis (Nalepa) is a grapevine pest and distributed worldwide. This study was conducted to identify grapevine damage related to density of C. vitis and to suggest an effective control time. The damaged flower buds displayed retarded growth and became dried up, and symptoms of damaged leaves such as malformed and bronzed leaves were observed. Flower cluster and leaves were collected and density of the grape rust mite were observed by using a washing and sieving method. The highest mean density (±SE) of C. vitis was found to be 672.6±112.9 per flower cluster with mid-level damage, and 450.1±66.5 per 2 leaves was found on the damaged leaves. These severe damage symptoms were observed in the early spring, and the density of the grape rust mite was significantly higher as 80 times in damaged vineyard than in the undamaged at the early growth stages of the grapevine. To determine the emergence time of the grape rust mite from lower part of a winter bud the ratio of density of C. vitis on upper-bud to lower-bud was observed. On 13 April 2015, 80% of the grape rust mites were observed on upper-bud where the mite could feed at the bud burst stage. Therefore, once the symptoms of damaged flower clusters and leaves are observed, acaricides should be sprayed before inflorescence emergence, and at the early growth stage between bud burst and leaf development in following year. This would allow the decrease of the density of C. vitis in early spring, and the progression of severe damage could be prevented.

• Sun Kyung Lee(Entomology Program, Department of Agricultural Biotechnology, Seoul National University)
• Jae Seong Im(Entomology Program, Department of Agricultural Biotechnology, Seoul National University)
• Jong Kook Jung(Research Institute of Agriculture and Life Sciences, Seoul National University)
• Joon-Ho Lee(Entomology Program, Department of Agricultural Biotechnology, Seoul National University, Research Institute of Agriculture and Life Sciences, Seoul National University)