One question often asked of Master Gardeners and extension agents is, "How do I keep fruit flies from stinging my fruits and vegetables?"
It is difficult to completely eradicate fruit flies because there are so many wild host fruits, such as guavas for Oriental fruit flies, wild bitter melon and ivy gourd for melon flies, and coffee for Mediterranean fruit flies. However, there are some strategies that gardeners and farmers can use to reduce the fruit fly population.
The most basic is to remove fallen fruits and vegetables that might host fruit fly eggs and maggots. If left on the ground, the fruit flies will emerge and continue to infest your garden.
TRAPS
Use male lures in traps to monitor and reduce the adult male fruit flies. Because male lures attract specific male fruit flies, you will need to determine which fruit fly is infesting your fruits or vegetables. The Oriental fruit fly infests tropical fruits such as mango, lychee, papaya and guava, and is attracted to the lure methyl eugenol. The lure for Mediterranean fruit fly, which infests coffee, peach, persimmon and other fruits normally grown in cooler climates at higher elevation, is Biolure or Trimed.
The lure for the melon fly, which targets fruiting vegetables such as cucumbers, squash, zucchini and tomatoes, is Cuelure. There is a Malaysian fruit fly, also called the solanaceous fruit fly, that infests bell peppers, tomatoes and eggplant. The lure for this fly has not been effective, and it is not recommended.
Most gardeners use inexpensive plastic bottles with the male lures. The insects are attracted to the lure, enter the bottle in small holes drilled into the container and are either drowned in soapy water or cannot find their way out and eventually starve. If the dead fly solution is too smelly, you can omit the water.
BAITS
Use a protein bait with an appropriate insecticide to destroy both adult male and female fruit flies. One available bait spray product is GF 120, which already has the insecticide in it; another is Nu-Lure, which is a protein bait to which insecticide must be added.
Because the GF 120 bait already has the insecticide in it, you dilute it with water, approximately 1 part GF 120 to 5 parts water. For example, if you use 1 fluid ounce of GF 120, you would add 5 fluid ounces of water and mix it. Apply the diluted spray to the underside of the leaves of fruit trees such as mango. Mix only what you can use in one application. Do not save the mixed spray for another application.
If you want to spray Nu-Lure on your mango tree, for example, find an insecticide that can be used on mango, dilute it with water according to the label instructions, then add the Nu-Lure as directed.
If you are controlling melon flies on vegetables, spray the diluted bait spray on a border planting such as corn. The melon flies roost on plants such as corn and castor bean, then fly onto the vegetable plant to lay their eggs into the fruiting vegetable. It is more effective to apply the protein bait spray on the roosting plants, where the flies spend more time, than on the vegetable plant itself.
For more information on controlling fruit flies, call the Master Gardener help line on your island (visit www.ctahr.hawaii.edu/UHMG for contacts). The Master Gardeners hold workshops on controlling fruit flies and will show you how to make the traps, how to use the bait spray and where you can get the bait spray and male lures on your island.
The next fruit fly control workshop on Kauai is Jan. 7. Call 274-3475 to register.
Richard Ebesu is a University of Hawaii extension agent and Master Gardener coordinator at the Kauai Extension Office. You can reach him at rebesu@hawaii.edu or by calling 274-3475.
