Spotted-Wing Drosophila in Blueberries
Management of Spotted-Wing Drosophila in Georgia Blueberries
Spotted-wing drosophila, an invasive insect pest of Asian origin, has recently emerged as a devastating pest of blueberries in Georgia causing significant crop losses. UGA Blueberry Entomology program in collaboration with county extension agents conducted research and educational activities to help blueberry farmers implement effective season-long management programs to minimize crop losses due to this pest.
Blueberries are the biggest fruit crop in Georgia with an annual farm gate value of $284 million and economic impact of over $1 billion on the State economy. Spotted-wing drosophila (SWD), an invasive pest of Asian origin, has recently emerged as a major threat to blueberry production in Georgia. Since its first detection in Georgia in 2010, SWD infestations have led to 15-20% loss of blueberry crop annually. Georgia blueberry growers are very concerned about this problem because fruit marketers have zero tolerance for this pest and detection of even a single SWD larva in fruit can result in rejection of the entire shipment. Due to lack of information on biology and ecology of this invasive pest, growers have to make repeated applications of broad-spectrum insecticides to control this pest which is not a sustainable approach and could lead to resistance development in this fly and increase in secondary pest problems. Further research is therefore needed to develop more sustainable management programs.
In collaboration with blueberry growers and county extension agents, field trials were conducted at the University of Georgia Blueberry Research and Demonstration Farm in Alma, GA and at multiple commercial grower farms to evaluate multiple season-long management programs designed to serve the variety of grower needs. Detailed studies were conducted to evaluate effectiveness of organically certified products to control SWD in organic blueberries. We also evaluated effectiveness of adjuvants and phagostimulants to enhance the efficacy of insecticides. In our studies, we not only determined efficacy of various programs but also assessed non-target impacts of the management programs. Our results showed that season-long management programs can be developed to maintain effective control of SWD while keeping residue levels below Maximum Residue Levels (MRLs) established in United States and major export markets.
Several studies were conducted to investigate various aspects biology and seasonal phenology of SWD. Our results indicate that SWD flies are active in and around blueberry fields year-round and the trap captures were higher in the wooded areas surrounding blueberry fields. In another project, woodland habitats surrounding blueberry orchards were surveyed at seven sites in six major blueberry producing counties to determine potential wild host plants which can sustain SWD populations beyond blueberry field season and serve as source of new infestations in the spring. Our surveys and subsequent assays revealed that SWD can utilize a number of wild plants in woodland habitats surrounding blueberry orchards as alternative hosts when blueberries are not available in the field. Within a 24-hour period, SWD flies were most active in the blueberry fields during dawn and dusk when temperature in the field was pleasant and very little to no activity was observed during hot hours of the day or during the night. These results indicate that dawn and dusk would be the most appropriate times to make insecticide applications to directly target active flies rather than relying on residues in the fruit and foliage.
To make insecticide applications, blueberry growers employ a wide range of technologies and use different methods such as every row middle or alternate row middle but the level of coverage achieved by those specific technologies and methods has yet to be evaluated. We conducted studies to compare spray coverage achieved by sprayers most commonly used by blueberry growers, residue deposition on the fruit, and effectiveness of the spray residues against SWD. Spray coverage was uneven in different sections of the blueberry bush canopy in all treatments. Spray application using alternate row middle didn't provide sufficient coverage and SWD control.
A significant amount of rainfall occurs during the blueberry field season which can potentially wash insecticide spray residues off the blueberry fruit and foliage leaving blueberries unprotected from SWD. In order to help blueberry growers make informed decisions on re-treatment intervals after a rainfall event, studies were conducted to correlate the amount of rainfall to the residual efficacy of most commonly used insecticides. Our results showed that a rainfall event of more than 0.5 inches can significantly reduce the effectiveness of most of the insecticides and therefore insecticide should be reapplied to protect fruit from SWD infestation.
Based on results of our studies, we developed management recommendations in terms of season-long programs to enable growers to effectively control SWD in blueberries under conventional as well as organic production systems without compromising their ability to sell their fruit to U.S. and export markets of their choice. Communication with county extension agents, pest management consultants, and growers suggest that majority of the growers utilized our recommendations and consequently the total crop losses have significantly decreased than previous years with no fruit rejections due to SWD infestations reported from farmers using our recommended management programs. It has saved Georgia blueberry growers millions of dollars in crop losses due to SWD and increased profitability by enabling them to access export markets of their choice.