Two-spotted spider mites are a major issue in Florida strawberries. Justin Renkema, former assistant professor at the University of Florida (UF), says mites make their way into Florida fields by blowing in from neighboring fields, but they may also be coming on strawberry transplants from nurseries.
After proving that spider mites were coming to Florida on transplants, Renkema wanted to figure out how to get rid of the pests before the transplants reached Florida fields. “We looked at heating the transplants with steam to kill the mites, which is also being trialed for control of certain strawberry diseases,” he says.
Working in conjunction with UF pathologist Natalia Peres, Renkema began experimenting with steam at different temperatures for different durations to determine if heat would kill the mites. According to Renkema, the mites were placed on leaf discs and then placed in the “plant sauna” or steam chamber. “We tested 44° Celsius (111° F), 46° Celsius (115° F) and 48° Celsius (118° F), for either 30 minutes, one hour, two hours or four hours,” Renkema says.
He found that to kill 100 percent of the adult female spider mites, the steam had to at 48° Celsius for at least two hours. Renkema says that there is still more research to be done on the correct amount of time to apply the steam. “In two hours, we killed all of the spider mites. In one hour, we killed about two-thirds of them. So somewhere between one hour and two hours would be required,” Renkema explains.
Currently, Renkema is not recommending the steam technique because there is still much to be learned about it. Aside from finding the perfect amount of time, impacts on the actual transplant need to be determined. “We don’t want to kill leaves or impair plant flowering or growth,” he concludes.
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