Reducing copper and chlorothalonil in staked tomato production on Virginia's Eastern Shore

Virginia ranks third in fresh market staked tomato (Lycopersicon esculentum Mill.) production with approximately 1,659 hectares on the Eastern Shore. Estimated annual gross value is $30,800,000. Copper and chlorothalonil have long been considered essential to control bacterial and fungal diseases in fresh market tomatoes. High rates of these fungicides on tomatoes grown under plastic mulch have led to concerns about their potential adverse effect on water quality in estuaries adjacent to fields. The development of new fungicides, such as azoxystrobin and acibenzolar-S-methyl, which have more favorable environmental fate characteristics and are used at much lower rates, may provide viable alternatives to copper and chlorothalonil. Using a disease forecasting system, such as Tomcast, may reduce the number of applications of fungicides.

The research objectives of this study were to reduce the amount of copper and chlorothalonil used in fresh market tomato production and to evaluate the effectiveness of the Tomcast disease forecasting system for controlling fungal leaf diseases on the Eastern Shore. Field studies compared copper to acibenzolar-S- methyl for bacterial diseases caused by Xanthomonas campestris pv. vesicatoria and Pseudomonas syringae pv. tomato. Research plots were established in a randomized complete block design with four replications in grower fields and at the Eastern Shore Agricultural Research & Extension Center. Acibenzolar proved to be as effective as the standard copper bactericides in controlling bacterial spot. Acibenzolar provided better control than the standard copper bactericides when bacterial speck was the target disease. Azoxystrobin application alternated with maneb was evaluated as a replacement for chlorothalonil. Azoxystrobin and Tomcast were studied as tools to reduce chlorothalonil use for control of Alternaria solani. Tomcast can reduce the number of applications by 40-70 % per year and provide adequate control of early blight. Azoxystrobin provides better control of early blight than chlorothalonil. Use of these new, more environmentally compatible, plant-protection products , along with the Tomcast disease forecasting system, can significantly reduce or eliminate the need to use copper and chlorothalonil for tomato disease management and therefore eliminate them as potential pollutants of the Chesapeake Bay and Atlantic Ocean estuaries.