LAUSR

Abstract The grape rust mite, Calepitrimerus vitis (Nalepa), is an important grapevine pest worldwide. During the period of early spring emergence and movement to the overwintering refuge in the late season, growers need to control C. vitis properly. We developed forecasting models of early spring emergence and late summer overwintering movement of C. vitis in vineyards for control time. Their activation in the early spring was estimated by changes in density between upper bud and the whole bud. The density of C. vitis on buds was estimated using a washing out method. The proportion of C. vitis on the upper bud was increased as accumulated degree-day (DD) was increased. This relationship was well described by a linear regression model. Based on the model, 153 DD with a base temperature of 10.51 °C, at which emergence rate of C. vitis deutogynes was 70%, was proposed as the control time for C. vitis. Movement of deutogynes in the late summer was observed. The ratio of C. vitis movement for hibernation was increased as the relative night length was getting longer. This relationship was well described by a two-parameter Weibull function. Proportion of migrant deutogynes was low in August. It increased sharply when relative night length was 0.499 (11.97 h, middle September). Therefore, control should be conducted before autumnal equinox in late summer at the latest.