Spotted wing drosophila (SWD) represents a serious threat to the livelihood of small fruit growers in the USA. This invasive pest is now present in 45 states, including all Northeastern states, decimating small fruit crop yield and quality. Losses are estimated to potentially reach $718 million annually. SWD attacks healthy, intact blueberries, caneberries, strawberries, and cherries by laying eggs in ripening fruit before harvest. Emerging maggots feed in the fruit causing rapid quality decline and consumer rejection. Threatened small fruit production in the Northeast alone includes 70,000 acres. Low thresholds for damage and infestation in fresh markets and zero tolerance for infested fruit for exportation have led some growers to either cease production or begin applying weekly or semi-weekly preventative insecticide applications in the absence of sensitive monitoring tools. This approach is not ecologically or economically sustainable. Alternative strategies for managing SWD in commercial small fruit operations that reduce the need for frequent insecticide applications, prevent outbreaks of secondary pests, and improve ecosystem services provided by beneficial arthropods are critically needed.
Ripening small fruit experience intensifying pressure from SWD, and in response, growers’ pest management practices have changed substantially; severely disrupting IPM programs or halting small fruit production altogether. Growers continuing to produce small fruit, protect them with frequent insecticide applications, and endure increased production costs plus secondary pest outbreaks. Additionally, because bramble crops can have both ripening fruit and blossoms on the same plant simultaneously, increased threats to native and managed pollinators exist.
Recruited Northeastern growers will incorporate SWD monitoring traps, frequent harvest intervals and/or attracticidal spheres as part of their SWD management programs in small fruit to demonstrate the benefits of incorporating IPM tactics. As monitoring traps continue to be refined, we will deploy standard designs on grower farms to determine if trap captures correlate with presence of fruit injury, thereby allowing for potential management decisions to be made regarding insecticide inputs.
We will also deploy an attracticidal sphere system that will effectively attract SWD adults to the red-colored surface, elicit feeding, and kill them with toxicant-laced sucrose. Flies attracted to spheres will be effectively removed from the foraging population. We will determine if particular deployment strategies for spheres improve overall performance and we will determine if harvest practices can improve overall system performance as well. The project team will conduct broad educational initiatives for the grower community via workshops, and field days at grower farms and research facilities.
Fifty farmers in the Northeast will adopt IPM-based strategies, such as attracticidal spheres, to aid SWD management on an average of 1 acre per farm. Adoption will result in up to 4 fewer insecticide applications per season for a savings of $91/acre in small fruit plantings
One hundred Northeastern growers will receive a survey to establish baseline information regarding current SWD management, secondary pests, pollinators, and willingness to adopt alternative strategies, including attracticidal spheres. Fifty growers will return surveys and participate in educational programs.
Over 150 growers were distributed. Surveys were completed by 74 growers from MD, WV, NJ and MI, all states with growers heavily affected by SWD in small fruit. Results of the surveys indicated that 68% of grower had SWD present on their farms with 66% reporting injury on 499 acres or 12.8 acres per growers. Over 77% used conventional insecticides, while only 42% use a monitoring trap, while 48% monitor for fruit damage. Over half of the respondents indicated that they were interested in using IPM-based management strategies for SWD.
Seven growers in MD, NJ, and WV will agree to collaborate in on-farm research trials to document the utility of attracticidal spheres for management of SWD. Each grower will receive twice-weekly team support for season-long management of SWD and other pests.
Attracticidal spheres were deployed at the top or bottom of small fruit plants on 7 commercial farms in WV, MD and NJ in blueberries, raspberries and blackberries. Spheres were deployed at a rate of 1 sphere every three meters in the upper third of the canopy, 1 sphere every three meters in the lower portion of the canopy, and no spheres as a control. Each plot was at least 1 acre in size. SWD fruit infestations rates were compared among treatments. For blueberries, SWD populations were quite low at the time of ripening, and no significant differences were observed. In raspberry plots, attracticidal spheres significantly reduced SWD in raspberry fruit compared with control plants (F = 6.8, P < 0.0001),though there was no difference if spheres deployed at the top or bottom of the plants. Attracticidal spheres did not reduce SWD infestation rates in blackberry and will investigate why this is the case in future studies in 2018.
Finally, the team investigated if non-target pollinators and beneficial insects visited attracticidal spheres. Spheres were observed during the morning and afternoon in flowering raspberry and blackberry plantings. A total of 18h of observation was conducted. During that time, over 1,500 beneficial insects visited plants with or without spheres, but only 2 syrphid flies and no bees landed on spheres indicated the risk to non-target organisms is low.