Written by Dylan Beal and Betsy Beers, July 1, 2022
Pressure from spotted-wing drosophila (SWD) varies from year to year. Some years (like 2015) with mild winters and early springs can produce high levels of pressure regionally, but some areas or orchards may have high (or low) pressure in most years. Trapping over multiple years will help you characterize where your orchard falls in this spectrum. Prophylactic sprays for SWD may not be necessary in low-pressure years or low-pressure orchards. It is important to distinguish between SWD and the other ‘fruit fly’, western cherry fruit fly (WCFF). WCFF is a quarantine pest with serious consequences, but you should work with your packinghouse to determine tolerances for both pests.
A bait spray, GF-120 NF Naturalyte Fruit Fly Bait has proven very effective against WCFF, but only partially effective against SWD. This is based in part on the formulation of the product and the biology of the pest. The thinking is that if you don’t have any SWD pressure (as determined by trapping), you can just protect against the quarantine pest, WCFF. And that can be done with GF-120 NF Naturalyte Fruit Fly Bait, especially as harvest approaches. Many broad-spectrum sprays will hit both pests, but also cause some non-target effects. And at some point, over-use of broad-spectrum canopy sprays may lead to resistance in either or both pests. And we don’t want that.
Trapping is the key to knowing about the pressure in your orchard. The Scentry Spotted Wing Drosophila Lure is the most attractive lure we have tested – better than apple cider vinegar or wine-vinegar mixes (liquid baits), or other home-made mixtures. The Trécé High Specificity Lure is pretty close. But the more attractive the lure, the more ‘by-catch’ you get – closely related species of Drosophila that are really hard to distinguish from SWD. Worst of all, in certain times of the year, the other Drosophila out-number SWD by about 1,000 to 1. This makes monitoring a tough process. A reasonable compromise is an attractive synthetic lure combined with a yellow sticky trap. This is a more selective than the liquid baits, or a synthetic lure over drowning fluid, and although not quite as sensitive, perhaps sensitive enough.
For more information visit https://treefruit.wsu.edu/crop-protection/opm/spotted-wing-drosophila/
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