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Detecting larval infestations and insecticidal options for Spotted Wing Drosophila, a significant pest of small fruit crops in Missouri
By Dr. Jaime C. Pinero
State Integrated Pest Management Specialist
Spotted Wing Drosophila (SWD) is a very serious new invasive pest that attacks small fruit
crops, some stone fruits (cherry, nectarine, peach), high tunnel tomatoes, and wild hosts
(including pokeweed, autumn olive, crabapple, nightshade, Amur honeysuckle, and wild grape).
Raspberries, blackberries, blueberries, and grapes are at the greatest risk. SWD flies look similar
to the small vinegar flies that are typically found around or on fermenting fruits and vegetables.
However, unlike those native vinegar flies, SWD females have a serrated egg-laying device
(called ovipositor) to cut a slit into the skin of intact fruit to lay their eggs. This makes SWD a
more significant pest. An identification and monitoring guide has been developed by the Lincoln
(LU) IPM program. It is available at: http://www.lincolnu.edu/web/programs-andprojects/ipm.
This article discusses how to detect larval infestations and management of SWD based on
key IPM components listed below. A SWD control program starts with monitoring. If SWD is
detected, chemical control is necessary to preserve the marketability of fruit. For commercial
growers, some chemicals already used in your IPM program for similar pests should give
effective control of SWD.
1. Monitor fields with traps and check them
2. Check trapped flies to determine presence and
number of SWD.
3. If SWD are found and fruit are ripening or ripe,
apply effective insecticides registered for that crop
to protect the fruit until harvest is completed.
4. Continue monitoring to evaluate your
management program, this time checking traps
twice a week, and respond quickly if needed.
5. Use cultural controls where possible (mainly
removing old, infested, or damaged fruit from the
field) to reduce SWD food resources.
6. Stay informed. These recommendations are
subject to change based upon new information.
Use of effective insecticides that are well
timed and have good coverage can keep
SWD controlled through harvest.
However, given the potential for rapid
population increase by SWD, especially
during fall red raspberry season, means
that active management through
monitoring of flies and fruit infestation
is critical. Always follow the specific
label restrictions for raspberry /
blackberry crops. The level of control
achieved will depend on the SWD
population, timeliness of application,
coverage of fruit, and product
DETECTING LARVAL INFESTATIONS IN FRUIT
The following recommendations are largely based on guidelines provided by Michigan State
University (MSU) and Oregon State University (OSU). A first sign of SWD infestation in
raspberries may be noticed as red patches left on the receptacle when the berries are picked.
The fruit of raspberries and blackberries may also begin to collapse in areas where the larvae
are feeding inside. Opening the berries may reveal the larvae within the fruit, but it is time
consuming to check individual berries. Fruit can be selected in 2 ways, either by collecting fruit
at random, or by collecting only fruit you suspect is infested (i.e., the presence of oviposition
scars and/or soft spots on the fruit).
(i) Sugar-water method: Place fruit in a plastic “ziplock” bag and crush lightly to break the skin.
Then add a sugar-water mixture (4 cups water to every 1/4 cup sugar). SWD larvae will float in
the liquid and the fruit will sink. Detection of small larvae may require the use of a hand lens,
and this works well with a light behind the bag to create backlighting
(ii) Salt-water method: A salt solution will irritate the larvae causing them to wiggle out of holes
in the fruit. To prepare a salt-water solution, dissolve 1/4 cup plain salt in 4 cups warm water.
Place fruit in a shallow white pan and cover with salt solution. Observe the fruit closely for at
least 10-15 minutes to see larvae exiting fruit out of egg- laying holes. Detection of small larvae
may require the use of a hand lens and good lighting. Count as quickly as possible while they
are still alive and moving.
Because this pest is so new to Missouri, there has been no research on insecticidal treatments
to manage SWD and therefore recommendations are based on findings from other states.
Before you spray, confirm that you have SWD in your area by hanging out traps or checking
fruit. Sprays must be timed to kill adults before they lay eggs, as sprays will not control larvae
already in the fruit. Always read product labels to make sure pesticides are registered for use
on the fruit or berry you are treating.
If monitoring indicates a need to spray, the application should be made about 2 to 3
weeks before berry harvest. Depending on the residual effectiveness of the insecticide, a
second application may be needed 5 to 10 days later. In the case of indeterminate fruiting
berries such as raspberries or strawberries, sprays might need to be repeated to keep
populations low during summer and fall. You can use monitoring traps to help you decide if and
when additional sprays might be needed. Be sure to wait the interval specified on the pesticide
label before harvesting fruit. Thus far an economic threshold for SWD has not been developed.
MSU recommends a conservative approach in which fly capture on your farm triggers
protection of fields if berries are at a susceptible stage.
For commercial raspberry and blackberry farmers – conventional. A number of registered
insecticides have been very effective against SWD in laboratory trials, including some recent
trials done at MSU. The most effective chemicals are organophosphate, pyrethroid, and
spinosyn classes of insecticides. Under field conditions, insecticides with fast knockdown
activity have performed well at protecting fruit. Insecticides with fast knockdown activity have
performed well at protecting berries from SWD. These include Malathion which is an
organophosphate insecticide; the pyrethroids Danitol, Mustang Max, and Brigade; and the
spinosyns Delegate (spinetoram) and Entrust (organic). Delegate 25WG has been labeled for
control of SWD in various crops in all States. Neonicotinoids such as Provado and Actara are
considered weakly active on SWD flies and are not recommended for control (MSU info).
For commercial raspberry and blackberry farmers – organic. In bioassays conducted by MSU
with Azera and Pyganic these options performed less effectively than Entrust. However,
pyrethrum class insecticides can still be a valuable tool for organic growers because the Entrust
label requires rotation to another product for resistance management. Pyganic or Azera can
very well fit that need. Entrust is the only organic product with residual activity (5-7 days
control). While it doesn’t appear to provide residual control, Pyganic® applied at 5 day intervals
at the high labeled rate has shown to reduce SWD populations in California. Organic growers in
the Pacific Northwest have used 2-3 applications of Entrust (spinosad) effectively to protect
fruit in the pre-harvest period alternated with Pyganic (pyrethrum) to extend the period of
control and also to reduce the chance of resistance development.
For home-owners. The insecticide Spinosad (e.g., Monterey Garden Insect Spray) is effective
and has the least negative environmental effects of currently available products. Some spinosad
products are sold to be applied with a hose-end sprayer, but a compressed-air sprayer will give
more reliable coverage. Fertilome® Borer, Bagworm, Tent caterpillar and Leafminer spray
(spinosad 0.5%) and Green Light® (spinosad 0.5%) are also labeled for use in bushberries and
caneberries against fruit flies. The organophosphate insecticide malathion is widely available
and will also control SWD, but malathion is very toxic to bees and natural enemies of other
pests in the garden so care must be taken to keep the application on the target plant and avoid
drift and runoff. Improper application also can result in injury to cherry trees. Because of the
potential negative impact of malathion in the garden, use it only where you are certain you will
have a SWD infestation, either because you had a problem last year or from trapping and
positively identifying insects this season as SWD.
Table 1. Insecticides for SWD control. Products are not complete listings of all available options.
(H) signifies that the product is registered for homeowner use, (O) signifies an organically
compatible insecticide. Not all products are labeled on all fruits; read label to ensure that your
product matches the site. Alternate the MoA (mode of action) of the product you choose on a
yearly basis to minimize resistance build-up.
INSECTICIDAL CONTROL CHART
1 - For use against SWD on various crops in all US states
2 - Labeled for use against fruit flies (SWD is a ‘vinegar’ fruit fly)
3 - For use against SWD in strawberry in 12 US states, MO is not included
4 - For use in all US states except NY
Registrations and recommendations change, so keep informed through SWD websites and your localExtension educator. For all pesticides, consider REIs, PHIs, surface water and buffers, and safety to pollinators and other beneficial arthropods when selecting a product. Remember to rotate classes of insecticides to delay possible development of insecticide resistance.
To address pollinator safety, make
early morning or late evening applications of all products.
As with all uses of insecticide to control pest insects, the label is the legal document that provides the official guidance on the appropriate use pattern. Refer to the label and any supplemental labels for the full restrictions on use in your crop. A good place to locate all the most up-to-date information is through http://www.cdms.net/labelsmsds/LMDefault.aspx. If new supplemental labels are developed allowingexpanded uses for SWD control, those will be posted at this site
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