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.
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)
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