As a follow up to Phil’s earlier post about managing sour rot and spotted wing drosophila (SWD), I just want to mention that grapes are now becoming attractive to SWD, so if you have had issues with SWD and/or sour rot in the past, now is the time to start considering management options. The research that Phil discussed is encouraging, thus I would agree that it might be worth incorporating OxiDate with your insecticide sprays for SWD. Please note that we have not tested this in Georgia and while she recommends applying Mustang Maxx + OxiDate weekly until harvest, please make sure to rotate the insecticides with varying modes of action to help inhibit the development of insecticide resistance. See recommended insecticides and their modes of action below (always read and follow the label). Also note that the use of pyrethroids, like Mustang Maxx, especially when it is hot and dry, can flare mite populations, so when managing SWD keep an eye out for mites.
If you are unsure whether or not SWD is a problem at your vineyard, it is relatively easy to monitor for the flies. Traps can be made from plastic cups with lids.
- Approximately 1 inch from the top and 2/3 around the cup, cut or punch six to twelve evenly-spaced 3/16-inch-diameter holes.
- Fill the cup with 1-2 inches deep with bait.
- There are several bait recipes out there, but one of the easiest is using either straight apple cider vinegar or a mixture of red wine + apple cider vinegar (60:40, wine:vinegar), both with a drop of unscented soap to break the surface tension.
- Additionally, sticky card can be hung inside trap to catch flies
- Place traps on the north side of rows at fruit level.
- Females may be caught first, but are difficult to identify. Males have the characteristic spot on their wings (see image).
- For more information, check out: extension.psu.edu/plants/vegetable-fruit/fact-sheets/spotted-wing-drosophila/spotted-wing-drosophila-part-3-monitoring
Unfortunately capturing SWD flies in traps does not correlate with potential infestation of the fruit. In order to determine whether infestation has occurred and/or whether your management program is effective, you can monitor the fruit for SWD larvae.
- Collect intact, ripening or ripe grapes
- Place fruit in a flat, dark pan or zip-lock bag
- Add a salt solution (1⁄4 cup salt to 4 cups water)
- Wait ~15 minutes for larvae to exit fruit
- Larvae found in recently ripened fruit are most likely SWD (see image).
- If larvae are found, begin or continue management program.
- The full life cycle from egg to adult for SWD can be as quick as 9 days, so continue to monitor and manage until harvest.
- Note that flies will infest fallen fruit and discarded fruit, so waste disposal and sanitation are important
Management recommendations can be found at: https://www.smallfruits.org/SmallFruitsRegGuide/Guides/2016/BunchGrapeSprayGuide2016.pdf