Steam-based thermotherapy for managing nematodes in strawberry transplants

Aerated steam-based thermotherapy was developed and evaluated for its efficacy in managing three nematode species (Aphelenchoides besseyi, Meloidogyne hapla, and Pratylenchus penetrans) that are often transported as quiescent passengers on strawberry transplants shipped to Florida from out-of-state nurseries. Initial studies were focused on evaluating the intrinsic temperature sensitivity of each nematode species to hot water in laboratory conditions. Each nematode species was exposed to hot water at 40, 44, 48, and 52°C for 1, 5, 10, 30, 60, 120, and 240 min. Exposure for 60 min or higher at 40°C paralyzed all three nematode species when examined immediately after heat treatment. Examination of the nematodes 24 hr post-treatment suggested that 100% mortality of all three nematode species was achieved when nematodes were exposed to hot water at a minimum temperature of 44°C for 120 min. Further studies were conducted to evaluate the efficacy of aerated steam to kill all three nematode species by exposing nematode-infested strawberry transplants at 44°C for 60, 120, and 240 min. Exposure of nematode inoculated plants to steam for 60 or 120 min reduced the populations of all three nematode species, but this was not enough to completely eradicate any of the three nematode species. Exposure for 240 min, however, was the most effective in reducing the populations of the three nematode species. A 240 min of exposure to aerated steam completely eradicated A. besseyi and M. hapla while P. penetrans populations were reduced only by 85%. Furthermore, the aerated steam had minimal to no adverse effect on plant biomass. Results from both the laboratory and greenhouse studies indicated that M. hapla was more sensitive to heat treatment followed by A. besseyi and P. penetrans. Results from this study suggested that aerated steam-based thermotherapy has good potential as a non-chemical method of management of nematodes of strawberry transplants.