Special to The Sun
A new invasive species has begun flying around and pestering fruit growers in Oklahoma.
A Tulsa County grower recently captured a suspicious looking fly. The grower called the Tulsa County Extension Office who shipped the insect to Oklahoma State University’s Department of Entomology and Plant Pathology for identification. The OSU Plant Disease and Insect Diagnostics Laboratory confirmed the capture as the spotted wing drosophila.
The rather small vinegar fly or fruit fly attacks ripening or ripe soft fruits including blackberry, blueberry, boysenberry, grapes, raspberry, strawberry and tree fruits (peach, apricot, cherry, mulberry, nectarine, persimmon and plum). The SWD also has been known to attack melons and tomatoes.
“Spotted wing drosophila was first detected in the United States in California in 2008, where it eventually spread north to British Columbia and south all the way to Florida,” said Phil Mulder, EPP department head. “As recently as 2012, SWD was confirmed in Arkansas, Colorado, Idaho, Illinois, Indiana, Iowa, Kentucky and Minnesota.”
Based on its rapid movement across the country and the fact these flies cannot fly very far, it is thought to be spread by humans transporting infested fruits.
“What makes SWD potentially more economically important than other fruit flies is its ability to cut into intact fruit, using their serrated ovipositor to inject eggs under the skin,” said Eric Rebek, OSU Extension entomologist. “This allows the subsequent larval stage to be present during ripening and can lead to detection in ripe fruit after harvest.”
Oklahoma fruit growers should be mindful of three important components in effective management of SWD. The first step is monitoring, which can be easily conducted through a simple trap baited with pure apple cider vinegar.
“Identification is the second component, which can be difficult for the untrained eye. These tiny flies are only 2–3 millimeters in length,” Mulder said. “Male SWD possess a shadowy spot near the apex of each forewing, while females lack these spots.”
The females have a distinct ovipositor with two rows of serrations longer and darker than other vinegar flies. For help with identification, samples can be submitted to the OSU Plant Disease and Insect Diagnostics Laboratory (http://entoplp.okstate.edu/pddl/pdidl).
“Once SWD have been detected, management activities should begin immediately,” said Jackie Lee, pesticide coordinator for the Division of Agricultural Sciences and Natural Resources at OSU. “From a cultural standpoint, growers can minimize the population buildup by harvesting on time and removing overripe fruit and wild hosts such as wild grape, raspberry and blackberry from nearby locations.”
If an insecticide is applied for control, selection should be based on several factors including harvest date, re-entry restrictions, impact on existing Integrated Pest Management (IPM) programs, beneficial insects and environmental conditions.
Spinosyns (Delegate®, Success® Entrust®) and organic pyrethrum (Pyganic®) insecticides have shown activity on this pest, but so have some of the carbamates (Sevin® or Lannate®), organophosphates (Imidan® or Malathion®) and pyrethroids (Asana®, Brigade®, Danitol®, Mustang-Max®). Azadirachtin (Aza-Direct®) also has proven to be effective.
“Irrespective of the choice of insecticide, it is imperative growers strictly follow restrictions regarding harvest and re-entry,” Lee said. “In addition, it is also important to rotate between the various chemical classes to avoid development of insecticide resistance.”