Investigation of Argentine ant biology and control methods in California vineyards

Argentine ants exacerbate grape and obscure mealybug populations in coastal California vineyards. Available ant controls are either toxic, broad-spectrum pesticide sprays, which disrupt natural enemies and are only moderately effective at controlling ants, or dry proteinaceous baits, which are unattractive to sugar-feeding ants. Over the last 5 years, we have worked to develop a sustainable ant control program, dispensing reduced-risk insecticides in sugar baits. These baits do not disrupt non-target species, nor do they contaminate groundwater (a concern with barrier insecticide sprays). Originally our system, although effective, was labor and material intensive, both of which were prohibitive to its adoption on a large scale by growers.

In 2004, we began testing a bait dispenser to replace previous models. We further updated the design of the dispenser in 2005, and report significant reductions in ant populations in treated blocks, with a corresponding decrease in economic damage to clusters. Subsequently, this bait station was accepted for use by CHEMSAC (US EPA), and can now be deployed in agricultural systems. In 2005, we also advanced registration of a product to fill these stations, one of which should be available no later than 2007. Registration of this product is based on 2 years of data demonstrating its efficacy in vineyard systems.

In 2005, we studied several aspects of the ant bait program in an attempt to decrease the cost of implementation and increase the efficiency of application. We delineated patterns of ant dispersion in two San Luis Obispo County vineyards, which show that during the winter months the ants were concentrated in riparian areas and moved progressively further into the vineyard from winter to harvest-time. This description provides better information to manage the spread of the pest, and suggests that bait stations may be strategically placed at the edges of fields to minimize ant movement into the field. We concluded studies of ant nest phenology, to ensure that baiting precedes and/or coincides with a period of intense brood production. We initiated a study of bait station densities and measured the relationship between the number of bait stations per acre and the level of ant activity. Initial data from temporal studies suggest that early-season baiting is preferable to late-season baiting, with significantly less economic damage to clusters in plots where baiting began in April as opposed to July. We studied Argentine ant foraging behavior and found that initial movement of sugar water baits is limited to the area within 50 feet of a bait station.

These studies provide the background information necessary to answer questions posed by growers regarding bait placement, initiation and duration of baiting, and density of bait stations per acre, allowing us to optimize the efficiency and effectiveness of the ant baiting program.