The "1-2-3" IPM Approach for Spotted Wing Drosophila Management

Be on the lookout this year for the Spotted Winged Drosophila.  It is expected to be in every county this growing season.

This document briefly discusses the most relevant Integrated Pest Management (IPM) practices that are recommended for Spotted Wing Drosophila Management (SWD) in berry crops. The “1-2-3” approach to SWD management is meant to provide easy-to-understand steps to manage SWD in small farms. The three main components being discussed here are monitoring, cultural practices, and timely application of insecticides.

1. Monitoring

For 2014, a monitoring program for susceptible crops is recommended throughout the harvest season. Place one monitoring trap baited with active dry yeast (1/2 tablespoon), sugar (2 tablespoons) and water (6 ounces) every 2-3 acres (Washington State Univ. recommends 1 trap in each crop or 1 trap per acre for large plantings). The trap needs to be hung on a plant, stake, or trellis 3–5 ft. or feet above the ground on the most shaded / coolest side of the plant canopy.

Articles discussing the importance of SWD monitoring, trap construction, and monitoring protocols can be found at Lincoln University's IPM website.

2. Cultural Practices

Cultural controls are practices that reduce the establishment, reproduction, dispersal, and survival of immature SWD.

o    Sanitation: Fruit should be harvested frequently and completely. Culled fruit should be removed from the field and either frozen, “baked” in clear plastic bags placed in the sun, or disposed of off-site.

o    Canopy and water management: Prune plants to maintain an open canopy. This may make plantings less attractive to SWD and will improve spray coverage. Leaking trickle irrigation lines should be repaired, and overhead irrigation should be minimized. Allow the ground and mulch surface to dry before irrigating to increase the likelihood that larvae/pupae of SWD in the soil will desiccate and die.

3. Insecticide Sprays

No action threshold is available for SWD and in other states traps have not consistently been able to detect adults prior to fruit infestations. Based on this information, Michigan State University researchers are recommending a more conservative approach involving application of insecticides when SWD are captured by monitoring traps and the crop being protected has the first fruit beginning to soften and turn color.

Assessing the efficacy of an IPM program targeting SWD

It is important to highlight that an IPM program includes the use of monitoring traps to assess adult SWD population levels. Quantifying fruit infestation through fruit sampling is critical to determine the effectiveness of control systems implemented against SWD.

1.   FRUIT SAMPLING: North Carolina State University researchers suggest sampling at least 30 fruits from each field to determine insecticide spray efficacy.

2.   DETECTING LARVAL INFESTATIONS: Fruit infestation can be analyzed through various methods. Five methods are discussed below (source: NC State):

§  Sugar flotation: Add ¼ cup sugar to 4 cups water then lightly crush the fruit to break the skin. Place fruit and sugar-water in a one gallon zip bag and observe larvae. The larvae should float and the fruit should sink, but this isn’t always the case. A hand lens may be needed for small larvae.

§  Salt extraction: Place fruit in a flat container in a thin layer. A dark container or a clear container against a dark surface works best. Pour salt water (1/4 cup of salt per gal of water) over fruit. After 10-15 minutes, larvae will exit fruit. If no larvae are visible, gently crush fruit to ensure salt water has penetrated. Keep in mind that larvae are more visible when moving; however, immersion in salt water will eventually kill them.

§  Freezing or chilling: SWD eggs and larvae cease development at temperatures less than 41F, likely preventing further damage to the fruit. The longer fruit are stored and the cooler the temperature of storage, the more likely that small SWD larvae will die. Holding fruit at cooler temperatures also give growers the added benefit of determining how significant the infestation, as large larvae will exit fruit as it cools. To do this, place fruit into a sealed, clear plastic bag and freeze or refrigerate overnight. Larger larvae will exit fruit and typically die on the surface of the fruit or the bag but small larvae may not exit fruit.

§  Direct observation: directly crush or cut the fruit, larvae may directly observed (a hand lens may be needed).

§  Rearing flies out: Since it is practically impossible to tell SWD larvae from other vinegar fly species, then holding larvae and pupae in a container with ventilation until adult flies emerge is currently the only definitive way to confirm SWD infestations. Fruit should be held at room temperature for up to 14 days to ensure all adults will emerge.

For the last five years or so, researchers have been evaluating numerous insecticides to identify the products that provide effective SWD control while reducing negative impacts to non-target organisms including pollinators. A number of registered conventional insecticides have shown to be effective against SWD in recent trials by Michigan State University researchers. Insecticides with fast knockdown activity such as the organophosphate Malathion*, the pyrethroids Asana (esfenvalerate), Danitol (fenpropathrin), Mustang Max (Zeta-cypermethrin), and Brigade (bifenthrin), and the spinosyns Delegate and Entrust (organic) have performed best. In a recent paper, researchers from Michigan State University (Van Timmeren and Isaacs, 2013) documented that spinosad (Entrust) and Spinetoram (Delegate) consistently performed as well as some pyrethroids such as Zeta-cypermethrin (Mustang Max). Malathion also showed good performance. Most insecticides lost efficacy after rainfall, and one of the exceptions was Zeta-cypermethrin (Mustang Max). Efficacy of most treatments was reduced greatly after exposure to just over 2 cm of rain. By one week after treatment adult mortality was not significantly different from the untreated controls for most insecticides that had been exposed to rain.

(*While effective at suppressing SWD, malation degrades with UV light, therefore increasing the rate could help mitigate the effects of environmental degradation of this insecticide.)

Research done in Florida also indicates that Danitol, Mustang Max, and Delegate performed equally well at reducing adult SWD activity and injury to blueberries.

References
Lincoln University IPM program: http://www.lincolnu.edu/web/programs-and-projects/ipm and http://www.LU-IPM.net 
Michigan State University: http://www.ipm.msu.edu/invasive_species/spotted_wing_drosophila 
North Carolina State University: http://ncsmallfruitsipm.blogspot.com/p/spotted-wing-drosophila-general.html 

Oregon State University: http://spottedwing.orgCornell University SWD website: http://www.fruit.cornell.edu/spottedwing/ 

(by Patrick Byers, MU Regional Horticulture Specialist and Dr. Jaime Pinero, LU IPM Specialist)