Validation of a Spotted Wing Drosophila Growing Degree Day Model for the Southeast for Sustainable Blueberry Production

View the project final report

Commodities

• Fruits: berries (blueberries)

Practices

• Pest Management: integrated pest management

There is a need for technologies that will enhance or increase the efficacy of alternative methods to control SWD as a means to reduce or eliminate pesticide usage. We propose to employ a modified Growing Degree Day Model to counter the growing threat of SWD in the Southeast Growing degree days (GDD). Based on the amount of heat units accumulated in a specific area, this model will allow growers to predict the occurrence of the various life cycle stages of plants and animal species. Specifically, the GDD model allows growers to know when the first appearance of an insect pest is in fruit their production systems, when egg laying activities occur, the emergence of new adults, and peaks in population growth. Being able to predict when a particular life stage of an insect will occur will enable growers to apply sprays targeted for a specific life stage. Additionally, spraying with such specificity will enhance the overall efficacy of softer chemistries or other non-chemical control options such as ‘catch and kill’ or mass trapping.

Researchers in the Pacific Northwest have developed a GDD model for SWD. Validation of this GDD model must be conducted for the climate of the Southeast given the vast differences in climate between the two regions. The proposed objectives of this study are to:

1) Validate the SWD GDD model developed for the Pacific Northwest for accuracy in the southeastern climate of Alabama, and

2) Provide supporting data for larger studies that will result in more effective control of SWD using more sustainable practices such as softer chemistries or ‘catch and kill’ or mass trapping strategies.

Meeting these two objectives will assist us in applying for the SARE Research and Education funding opportunity to further our research efforts to increase sustainable practices in blueberry production.

This study will be conducted at an on-farm blueberry orchard in Chilton County in Central Alabama (32.097°N 86.683°W), which is a major fruit producing region of the state. An additional study will be conducted on a blueberry orchard (32.532° N 85.431° W) near Auburn, AL, which fully adopts organic production practices.

Trap Construction and Bait Preparation. Spotted wing drosophila traps will be constructed from red, 12 oz Solo cups. Restaurant grade plastic tops will cover the opening to prevent escape of captured fruit flies. A black strip border will be painted around the circumference of each trap 2.5 cm below the lip. Corresponding to the black border strip, 0.9 cm holes spaced 0.15 cm apart will be drilled over the entire circumference of the cup, 1 cm below the lip to allow SWD to gain entrance. To construct hanging supports, additional opposing holes will be drilled in the traps. One end of a 20-gauge copper wire or material providing a similar function will be inserted in the hole and bound to prevent slippage of the wire. The same will be done with the other end of the wire, which will enable the trap to be hung.   Each trap will receive 250 ml of a prescribed bait consisting 14 g active dry yeast, 118 cm3 granulated sugar, and 1.5 L water. Yeast/sugar baits were previously found more effective in trapping SWD than leading bait and is a cheaper alternative to manufactured baits (Burrack et al., 2015). Contents will be thoroughly mixed prior to placement in the traps.

Trap Placement and Data Collection. Traps containing yeast and sugar bait will be deployed in the field on February 1, 2020. Two traps spaced 25 m apart will be placed on opposing border rows of the blueberry orchard. Additionally, three traps will be placed along the border of a wooded area located near the blueberry orchard with the anticipation that wooded areas are where overwintered SWD are first detected. In order to determine GDD for each phenology stage, both monitoring of SWD traps and calculation of GDD will occur weekly. Phenology stages will include first flight (these will be overwintered SWD), initial presence of SWD in the blueberry orchard, peak population, egg laying, presence first generation SWD. Traps set along the wooded area will likely have the initial captures though all traps will be monitored. In addition to SWD phenology, the phenology traits of blueberry such as, date of first flower, fruit set, veraison of berries and harvest periods will also be recorded.

Environmental Monitoring. Ambient temperatures will be collected hourly using WatchDog A- 125 datalogger (Spectrum Technologies, Aurora, IL). Temperature data from dataloggers will be retrieved weekly using Specware Pro 9 software (Spectrum Technologies, Aurora, IL). Two dataloggers will be placed at the borders of wooded areas surrounding the blueberry orchards at each location and within the blueberry orchard. In blueberry orchards, a datalogger will be placed in the center of two opposing border rows as well as in the center of the orchard. At all locations, dataloggers will be placed 1.5 m above the ground. Monitoring of traps will continue until the end of blueberry season in mid-July.

Calculation of GDD. Calculation of GDD will begin on February 1, 2020 according to the GDD model developed in the Pacific Northwest. Calculation of GDD will be executed using the following equation as prescribed by Felber et al., 2018:

aGDD (k) = ∑ ^k_d=1 ∑ ^∞24_h=1 max (O,T_h (d)-T_b)

Where k is the upper limit summation, T_h is the temperature recorded at each hour of the day, which is represented by d. T_b represents the base temperature, which is 10 °C.