The Use of Aerated Steam as a Heat Treatment for Managing Angular Leaf Spot in Strawberry Nursery Production and Its Effect on Plant Yield

Xanthomonas fragariae, the bacterium causing angular leaf spot (ALS) of strawberry, is found routinely on strawberry nursery stock. Although ALS can be a serious disease in production fields, it can be particularly problematic in the sale and trade of commercial nursery stock because of international trade regulations. Heat treatment has been shown to be an effective treatment for managing ALS on nursery stock in small-scale experimental trials. The objective of this research was to design, build, and trial precision thermotherapy units for managing ALS for both research and commercial applications and to test a new thermotherapeutic protocol on strawberry nursery stock that combines a conditioning thermal treatment with an eradicative thermal treatment. Small-plot trials were conducted to evaluate the efficacy of precision thermotherapy on control of ALS using known sources of infected nursery stock. Additionally, trials were conducted in cooperation with commercial nurseries to determine the impact of thermotherapy on plant health and yield and on the natural development of ALS. In the small-plot trials, ALS incidence was significantly lower in plots treated with precision thermotherapy. In the commercial trials, precision thermotherapy had a variable, but negligible, effect on plant growth and yield. ALS, when it occurred, was always lower in thermotherapy-treated plots. Heat is a near-universal biocide. Thus, in addition to managing ALS, the commercial application of precision thermal therapy to strawberry nursery stock may be effective for managing a wide range of pest and disease threats to strawberry while simultaneously reducing pesticide usage. [Formula: see text] The author(s) have dedicated the work to the public domain under the Creative Commons CC0 “No Rights Reserved” license by waiving all of his or her rights to the work worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law. 2021