As two-spotted spider mites continue to be a serious issue in Florida strawberry fields, Justin Renkema, former assistant professor at the University of Florida, has been working with his colleagues to figure out where these spider mites come from and how best to manage them. He has conducted spider mite research over the past two strawberry seasons. Renkema presented his research at the recent Agritech Trade Show in Plant City, Florida.
A good portion of Renkema’s research involved finding out where the spider mites in Florida fields came from. He says spider mites were moving in from neighboring crops or vegetation on field edges. “Spider mites are moving from the Florida landscape into strawberry fields,” he says.
However, that is not the only origin of spider mite populations. Renkema says spider mites are also coming into fields from nurseries. “Plants from every nursery that we evaluated had at least some mites on them (sometimes in low numbers), but they’re still coming in,” he explains.
For control, Renkema says several effective conventional miticides are registered for use in strawberries. “There is a good opportunity for growers to use a rotation of products, all with different modes of action,” he says. It is crucial to rotate miticides to minimize the likelihood of spider mite resistance to any particular miticide.
Nursery growers may be using the same miticides as Florida growers. So, if plants receive multiple applications of a miticide in the nursery and subsequently in Florida fields, this may causes the miticides to become less effective more quickly. Research to date shows some loss of spider mite sensitivity to miticides when they are used multiple times in both nursery and production fields. However, Renkema says highly resistant spider mite populations were not evident in the experiments he conducted so far.
In addition to miticides, beneficial insects could be helpful in controlling spider mites. Renkema says some Florida growers are seeing good results from releasing predatory mites into their fields when the spider mite populations are low.
According to Renkema, sometimes growers may need to use a miticide before or after releasing predatory mites, which is an option because there are some miticides that will kill spider mites and not predatory mites. However, he says there were some questions about insecticides used to kill pests like thrips, and the impact those products could have on the predatory mites. “Some of them are highly toxic; some of them are totally non-toxic,” he says. Renkema suggests using recommendations from new University of Florida Institute of Food and Agricultural Sciences documents to find out which products are safe for the predatory mites.
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