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by Aaron Cato - June 8, 2020
Provided here are factors to consider when developing a management plan for spotted
Blackberry harvest is beginning across the state and our #1 insect pest, spotted
wing drosophila (SWD), is out and about in high numbers. Growers across much of Arkansas
should have already initiated insecticide applications to manage SWD. There are several
factors that can influence when you should start spraying and which insecticides you
should use, and we will discuss these below. Be sure to check out the Southeast Caneberry IPM guide from the Southern Small Fruit Consortium for more information.
How does SWD damage berries?
Damage from SWD is caused only by the larvae (immatures) and control should focus
on preventing adults from laying eggs in berries. The larvae of this species feed
on drupelets leading to the berry becoming soft and sunken making it unmarketable
(Photo 1). More importantly these larvae are visible to consumers, and detection of
infestations can lead to loss of part of your market. Considering it is hard to determine
which berries are infested, egg laying by the adults must be prevented to assure a
low risk of selling infested berries to consumers.
Photo 1 – Spotted wing drosophila (SWD) larvae feeding on a blackberry. Photo by Dr.
Rick Bessin, Univ. of Kentucky.
When is my blackberry at risk of infestation?
Drosophila fruit flies can generally only lay eggs in overripe or damaged fruit
which aren’t considered for harvest. SWD are a pest with major impact on berries because
they can lay eggs in ripening or ripe fruit that are previously undamaged and marketable.
When berries are beginning to turn color, from red to black, their skin begins to
soften enough for SWD to successfully lay eggs. This means that blackberries are at
risk of infection around 7-10 days before harvest.
When should insecticide management programs begin?
Insecticide management programs should begin no later than 7-10 days before your
first harvest. Use traps baited with a yeast+sugar solution or apple cider vinegar
to determine whether SWD adults are present in your planting prior to this timing.
If adult SWD are present more than 10 days before harvest, begin weekly insecticide
applications a week or so early. Be sure not to confuse SWD adults with other fruit
fly species that will also be present (Photo 2).
Photo 2 – Photo of spotted wing drosophila (SWD) adult flies. Males are identifiable
by black spots on wings and females by a serrated ovipositor. Other fruit flies that
look similar will have neither of these features. Photo and illustrations by John
Obermeyer, Purdue University.
Insecticide options for SWD
Insecticides that effectively control SWD are listed in Table 1 below. Four main
factors should be considered along with economics when choosing insecticides:
Table 1 – Effective Insecticides for Control of Spotted Wing Drosophila (SWD).
** Pyganic offers no residual activity and berries are potentially at risk the day
How to determine if Control Efforts are Effective
It’s important to understand how effective your management efforts have been
because failures that slip through can negatively impact market sources. Take a representative
sample of your planting consisting of 50-75 berries. Put these berries in gallon sized
bags or a metal pan that contains a salt water solution (1 cup of salt per gallon
of water). After 15 minutes larvae will float to the top and infestation levels can
be assessed (Photo 3).
Photo 3 – Spotted wing drosophila assessment technique using a salt water solution
with raspberry. Larvae floating to the top after 15 minutes in the solution are indicated
by yellow circles. Photo by Jim Jasinski, OSU Extension.
Spotted wing drosophila (SWD) continues to be one of the biggest issues blackberry
growers in Arkansas face each year. Although there is a lot of thought that has to
go in to devising an effective and efficient management plan, most growers will find
that a high level of control is achievable. If you have any questions about the factors
mentioned here please give me a call or shoot me a text at 479-249-7352 or email me at firstname.lastname@example.org. Also be sure check out the Southeast Caneberry IPM guidefrom the Southern Small Fruit Consortium for more information.