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Chemical fruit thinning is a common practice implemented in commercial apple orchards to manage and regulate the number of fruit per tree (crop load) and consequently improve fruit quality and production. In this management practice, growers typically apply several sprays of chemical thinners to orchard blocks in the spring when the fruit is small and just beginning to develop. These thinning spray applications result in the abscission (detachment) of a percentage of the fruit. The occurrence of intentional fruit abscission or shedding is commonly referred to as “thinning.” Currently, chemical fruit thinning is the major means and standard practice of crop load management in apple orchards on the East coast. However, results can occasionally be variable due to the many factors (temperature, solar radiation, cultivar, etc.) which can affect the efficacy of the chemical thinners. These variable results can cause either under-thinning or over-thinning. As a result, proper chemical fruit thinning has come to be referred to as an “art” by many growers. Successful chemical fruit thinning in apple orchards is dependent on multiple factors but still relies heavily upon grower’s knowledge and experience. The purpose of this publication is to provide commercial apple growers with more insight in the predictability of using chemical thinners to better obtain desired thinning outcomes.
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Issued in furtherance of Cooperative Extension work, Virginia Polytechnic Institute and State University, Virginia State University, and the U.S. Department of Agriculture cooperating. Edwin J. Jones, Director, Virginia Cooperative Extension, Virginia Tech, Blacksburg; M. Ray McKinnie, Administrator, 1890 Extension Program, Virginia State University, Petersburg.
May 31, 2019