With the potential of the new fruit fly, Drosophila biarmipes, to become a problem in the Watsonville- Salinas fruit production district, it is important for growers to know what they might do to control it. The pesticides Malathion and Pyganic offer a measure of control against adult flies, and will need to be applied frequently, meaning once every week to 10 days.
Another pesticide which has been used with significant success in other areas of the country suffering fruit fly infestations is GF120 Naturalyte Fruit Fly Bait. Since it is a bait, GF120 is used differently than other pesticides, and it is worthwhile reviewing this with applicators and growers.
Being a bait means that GF120 draws the target pest to it, instead of having the pesticide delivered to the pest. This means that coverage and distribution is far less important with GF120 than with regular pesticides.
Indeed, this is the case because in most cases the application rate of GF120 plus water carrier is less than one gallon per acre. Obviously, it will not be possible to apply GF120 with an airblast or rowcrop sprayer because the rate is so low. One must use equipment which can apply very low rates, such as the hand held sprayer pictured below, to apply this material. There are also automated sprayers in use in the Central Valley for olive fruit fly control specifically for application of this bait.
Distribution of GF120 means applying a spot (around 2-3 milliliters) of the material (see second photo below) over fairly widely spaced intervals in the field. In the trial conducted this past winter, it was found that every thirty feet on each side of a raspberry hedgerow was sufficient to reach the rate required by the label.
While there are no restrictions on the label concerning contact of GF120 with berry fruit, it is suggested to avoid contacting the fruit with the bait as it does not taste very good. In raspberries, spray to the base of the hedgerow some two to three feet off of the ground. This seems to be where most of the flies are found anyway, so this serves a second purpose. In strawberries, it is probably best to spray between the plants during the early part of the season when the canopy has yet to close and then towards the midtier where there is less fruit when the plants are larger.
Mixing of GF120 is important. While soluble in water, it takes significant agitation to go into solution, more so than most other pesticides. It is vital that GF120 be properly mixed, because unsuspecting applicators could end up applying the bulk of the active ingredient in the first run of the application and water on the rest. Additionally, it is very thick when not well mixed and clog the lines. Once properly mixed, it does not come out of solution.
Finally, the label for GF120 recommends re-application every one to two weeks, depending on weather conditions. Rain will wash the bait off and sun breaks it down over time. Our experience in macro-tunnels informs us that the bait lasts longer in the protection of the tunnels, but even so, it is advisable to re-apply every three to four weeks.
There are several insecticides mentioned for control of fruit flies in this article. Before using any insecticides, check with your local Agricultural Commissioner's Office and consult product labels for current status of product registration, restrictions, and use information.
Equipment suitable for GF120 application.
GF120 as applied on leaves.
Drosophila biarmipes female feeding on recently applied GF120 Fruit Fly Bait.