IMPROVING THE EFFICACY AND SUSTAINABILITY OF PEACH DISEASE MANAGEMENT STRATEGIES: INCORPORATION OF BIOFUNGICIDES AND REFINEMENT OF COVER SPRAY PROGRAMS

Peach blossom blight and rusty spot are two major diseases that need to be controlled by commercial growers. Significant blossom blight results in canker formation which provides inoculum for brown rot later in the season. In disease-favorable years, 100% of a crop can be lost to brown rot. Rusty spot can also cause significant yield loss on susceptible cultivars. Unfortunately, resistant peach cultivars are not available for control of blossom blight and not all cultivars have sufficient resistance to rusty spot. Furthermore, there are nocultural control practices that can effectively manage these diseases. Consequently, disease control is dependent on application of fungicides. Thus, the first objective of this projectis to determine if biofungicides, many of which are approved for organic production, can be effective for control of peach blossom blight and/or peach rusty spot. Any biofungicides observed to be highly effective can be deployed alone in disease control programs, replacing conventional fungicides. Biofungicides that provide only partial control can be deployed in combination with conventional fungicides. Either approach will result in reductions of conventional fungicide usage. Most biofungicides have lower levels of toxicity, which reduces harm to the environment and lessens applicator exposure. Conventional fungicide residues on fruit are also reduced by these programs.The second objective of this project is to refine a newly discovered approach to management of peach brown rot at harvest. Typically, brown rot is managed by application of two to three fungicide sprays during the final 21-day period prior to harvest. During this ripening period, the fruit become highly susceptible to brown rot infection and need to be protected by a fungicide. Unfortunately, most highly effective fungicides used at this time also have a high risk of resistance development in the brown rot pathogen. Consequently, fungicide resistance has already occurred in at least two, possibly three different fungicide classes in a number of peach and cherry producing areas in the eastern United States. A recent study showed that the summer cover sprays, applied to control other diseases such as peach scab, also provide control of brown rot at harvest. Further studies showed that cover sprays ofthe protectant fungicide captan consistently provided this additional control of brown rot. Since captan and other materials typically applied during the summer are primarily multi-siteprotectant fungicides, there is little if any risk of resistance development. Thus, application of captan cover sprays can reduce the pathogen population prior to usage of the at-risk fungicides, thereby reducing the likelihood of resistance development. This project seeks to refine this approach by determining the lowest possible rate of captan (to achieve the same benefit) and to determine if only end of season captan cover sprays can be effective. Further trials will also be conducted with sulfurto determine if higher rates can be as effective as captan for brown rot control. By reducing the risk of resistance, the summer cover spray program provides a mechanism for continued use of the highly effective site-specific fungicides against brown rot, the most important disease of stone fruit. The new approach requires no additional fungicide usage; growers only need to use the right fungicide at the prescribed rate in their standard cover spray program.