The goal of my applied research/extension program is to improve the management of important diseases of vegetable crops grown on Long Island with both conventional and organic production systems. Typically these diseases have been important elsewhere in the northeastern United States. To reach this goal, I am conducting research to increase our understanding of these diseases and to develop effective components for integrated pest management (IPM) programs. Specifically, I identify the sources of the disease-causing organisms, determine how these organisms survive between crops, develop scouting protocols and action thresholds for timing the initiation of fungicide applications after disease detection, investigate factors that favor disease development and use this information for timing fungicide applications, and evaluate new control tactics. Fungicide resistance can be an important consideration in managing diseases, therefore effort is devoted to studying its occurrence, its impact on disease control and its management. Diseases studied include powdery mildew, bacterial wilt and Phytophthora blight of cucurbit crops, white rust of spinach, bacterial leaf spot of pepper, early blight and powdery mildew of tomato, and black rot of crucifers. Management practices for improving soil health are being examined for their impact on plant diseases. Research is also being conducted to determine the impact on plant productivity of ambient ozone, which reaches concentrations that cause acute foliar injury to many crops each summer on Long Island.