Although mites don’t have the same pest status as codling moth or pear psylla, they are becoming more difficult to control in some areas because of resistance to pesticides.
In recent years, growers have had increasing difficulty controlling rust mites, which used to be low on the list of pests of concern, Dr. John Dunley, entomologist with Washington State University, Wenatchee, reported at the North Central Washington Pear Day.
Three species of mites are commonly found in pear orchards in the Pacific Northwest: two-spotted spider mite, McDaniel spider mite, and European rust mite. The importance of the various mites has evolved over time. Twenty years ago, McDaniel spider mite was the big problem, Dunley said. Now, the McDaniel mite can hardly be found, and two-spotted spider mite and European rust mite are increasing problems.
Damage thresholds for pear rust mite are so low that the predatory mite Typhlodromus occidentalis cannot be relied upon to control them, Dunley said. Biocontrol is a good goal, but tough to rely on in pears.
Growers tend to try to keep their pest control simple, using the same program year after year, but there are many products with different modes of action that they can use to avoid pests developing resistance to certain products.
New products include Zeal (etoxazole) and Fujimite (fenpyroximate), which were registered in 2004; Envidor (spirodiclofen) and Kanemite (acequinocyl), which were registered in 2005; and Acramite (bifenazate), which has been available under a Section 18 exemption. The new materials tend to be selective and are soft on predatory mites, Dunley said.
Older materials still available include Agri-Mek (abamectin), the standard control for spider mites and pear psylla, Nexter (pyridaben), Savey (hexythiazox), Apollo (clofentezine), and Vendex (fenbutatin-oxide).
Before mites developed resistance to it, Agri-Mek used to be the number-one choice for controlling pear psylla and spider mites.
Resistance of pear psylla and two-spotted spider mites to Agri-Mek has been seen throughout Washington State, and Dunley said he fears that pear rust mite is also developing resistance to the product. Vendex, an organotin, has been around for many years but has not been used much in recent years because of resistance. Dunley said it can be included in a rotation and might be one to consider using for serious mite outbreaks.
When deciding what to use for mite control, growers should consider the history of the orchard, the target species, and whether they need to control pear psylla also.
“If you had russeting by pear rust mite the previous year, you should probably stay on a control program,” Dunley advised.
Nexter or Pyramite (pyridaben) work well for European red mite, while Envidor, Zeal, Savey, and Apollo work well for both rust mites and two-spotted spider mite. However, Savey and Apollo are labeled for only one use per year.
Growers should look at what products they have used in the past, and avoid repeated use of products of the same chemistry, Dunley suggested.
“There are lots of options. Try to use materials only once per season—some are limited on the label to once per season. We’re trying to protect the materials and reduce the likelihood of resistance. Just because you’re in a soft program, it doesn’t mean you should not use resistance management and avoid using materials repeatedly.”
Miticides can be mixed with oil, which kills adults and enhances uptake of the product, as long as there are no concerns about phytotoxic effects on the tree.
Dunley also recommends postharvest and prebloom sulfur treatments where there’s a history of mite problems.