IMPROVED TIMING OF CONTROL FOR THE GRAPE BERRY MOTH, PARALOBESIA VITEANA, USING A DEGREE-DAY MODEL

The grape berry moth (GBM) Paralobesia viteana, is the key arthropod pest of grapes grown in the eastern US, requiring control in many regions to avoid significant economic injury. This injury is typically loss of berries due to GBM feeding, but additional significant losses can occur as a consequence of fruit rots brought on by the GBM damaged berries that can extend to entire clusters resulting in major crop losses. However, population size and potential for doing damage varies widely within vineyards on the same farm, from region to region and year to year. Hence, growers need reliable and effective methods for assessing risk from GBM, both in space and time, to make appropriate management decisions. One tool, originally developed in the 1970s and 1980s, is a trap baited with synthetic sex pheromone that attracts and captures male GBM. Pheromone-baited traps have been developed for a number of important moth pests and can be useful for understanding pest phenology, determining the need to apply an insecticide and timing of control measures. Unfortunately, the pheromone based lure, as currently employed, is only marginally useful for indicating the first flight of overwintered male GBM and not useful at all for indicating subsequent generations. Hence, there is a critical need for an alternative method to reliably time management decisions for GBM. Presently, the grape berry moth risk assessment protocol (GBMRAP) is the primary tool used by grape growers in the east to estimate timing of GBM management. For a high risk vineyard the protocol calls for an insecticide application at ten days post bloom (first generation GBM), early August (second generation), and if necessary, late August (third generation). As is true of other insects (and grapevines), development of GBM is temperature dependent. Although the recommended first spray is tied to bloom time, which in turn, is driven by temperature, the other timings are based solely on calendar date irrespective of temperature. In an average year the GBMRAP timings for control (using contact insecticides) may work fairly well but in cool years they may be applied early and in warm years they may be applied late. Hence, what is needed is a temperature based development or phenology model to provide growers with a more reliable method to time management actions. Such a model has been developed for GBM (Tobin et al. 2001, 2003) in which the number of degree-days (DD) for GBM to develop from eggs to egg-laying adult females is approximately 810 DD (F) (450 DD (C)) using a base developmental threshold of 47 F (8.4 C).