Summer rot diseases of apple can result in considerable production losses in warmer New York apple production regions. This project endeavors to understand the persistence and survival of apple summer rot pathogens as a means of refining disease management recommendations.

Summer apple rot diseases, black rot (Botryosphaeria obtusa), white rot (B. dothidea), and bitter rot (Glomerella cingulata) can severely impact apple orchard profitability in warmer production regions of New York. In addition to fruit rot, Botryosphaeria species in particular may also cause severe limb and trunk cankers on apple trees. A slight shift towards a warmer climate could result in an increased prevalence of these apple diseases in many apple production regions in New York. The older literature infers that apple rot pathogens survive in mummified fruit. However, no studies have investigated which pathogens or complex of pathogens reside in mummies, the extent to which pathogens overwinter in mummies, or the impact of production practices on pathogen presence in mummies. Specifically, there is little information regarding the impact of thinning and standard fungicide programs on pathogen presence or quantity of mummified fruitlets. It is also unknown if populations of these pathogens have developed resistance to the benzimidazole and Quinone outside Inhibitor (QoI) fungicides most frequently recommended for management.

Two years of data collected from surveys of experimental orchards in Geneva and at the Hudson Valley Laboratory suggest that both apple rot pathogens and several other apple pathogens colonize mummified fruitlets. Apple scab chemical management appears to have slight, but repeatable impacts on the number of mummified fruitlets retained through winter, but only on varieties that retain high levels of mummified fruitlets. Varieties that retain fewer mummies by comparisons do not appear to be affected by fungicides. Laboratory experiments are underway to investigate the impacts of fungicides on the internal colonization of mummified fruitlets. Preparations are being made to conduct field experiments in the 2008 growing season to investigate in the impacts on apple bloom thinners and growth regulators on mummified fruitlet retention and colonization.

This research will better define the role of fruit mummies in the development of apple rot diseases. One outcome would be the identification of factors that explain the observed prevalence of these diseases, including the possibility of fungicide resistance to benzimidazoles and QoIs. Other outcomes would include the identification of thinning practices and fungicide programs that impact the survival of apple rot pathogens. The identification of standard production practices that reduce disease inoculum could result in a reduction of unnecessary pesticide applications to control apple rot diseases.

My topic area is concerned with the prevention and spread of plant disease

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