We usually expect spotted-wing drosophila to be our main issue each year, and although
we didn’t have many in 2022, 2023 proved that rainfall and cool spell at the right
time could generate a lot of worms in fruit. Depending on where you are in the state,
you may have gotten rain almost every other day for the last couple of weeks. This
is a prime spotted-wing environment, regardless of the heat we’ve had. In addition,
we’ve already got several calls about stinkbugs in blackberries, and I haven’t been
to field yet where I can’t easily find them. The last two years were some of the worst
stinkbug years we’ve ever had and the early warm starts we’ve been getting the last
few years has made this sporadic pest a problem seem annual. See below for recommendations
on management of these two pests through the rest of the blackberry picking season.
Spotted Wing Drosophila Spotted-wing drosophila (SWD), Drosophila suzukii, is a familiar pest to most concerned
with berry production in Arkansas at this point but see this fact sheet by Donn Johnson for more on the biology of SWD. In 2021 we observed intense SWD infestations
and I believe we learned a lot of lessons about control in that year. In every instance
breakthrough infestations occurred where an acceptable spray program of at least every
7 days was in place. What was lacking in most cases was an effort to integrate cultural
control methods. This led to breakthrough populations that meant infested berries
in customer hands. Although populations were high again in 2023, growers who implemented
more cultural control measures saw a marked decrease in worms in their fruit compared
to 2021.
The main issue we seem to deal with each year is when to start the SWD spray schedule.
We often see many farms apply the first applications after the first harvest, which
yields many larvae in berries (Picture 1) . Research consistently suggests these first few sprays are the most important, and
growers need to use the best products first (bifenthrin, fenpropathrin, zeta-cypermethrin,
and malathion). A spray program during fruiting is a necessary facet of SWD management,
but without integration of cultural tactics, acceptable levels of control will generally
not be realized. This is especially evident in “bad” SWD years like we saw in 2021
and 2023 where populations quickly got out of control. Below I will go through some
ways to manage the environment on blackberry farms and make it less amenable for SWD.
Prune plants to maximize airflow and sun penetration. Research shows that SWD prefer
humid and cooler environments during the day.
Harvest fruit as soon as they are ripe. SWD are attracted to ripe or ripening fruit
and will lay eggs on blushing fruit when populations are high.
Increase harvest frequency when possible. This lowers the exposure time of ripe blackberries
to SWD adults which will mean less egg-lay.
Do not leave culls on the cane or deposit them within the field . Getting culled fruit out of plantings and disposed of will drastically reduce the
number of flies. This is one of the key areas where many Arkansas growers are hurting
their management efforts.Move berries to cold storage as quickly as possible. Getting berries close to 32°F
will slow/stop the development of eggs and larvae, and even kill many. There may be
trade-offs with berry quality when you move from hot berries picked in the late afternoon
to a cold facility. If problems occur consider a step-wise manner of cooling down
berries, but push the envelope as much as possible.
Tips to optimize spray programs:
Spray an effective insecticide at least every 7 days starting whenever fruit begin
to blush (Picture 2) or when your SWD traps indicate infestations are beginning in plantings.
Make sure your first insecticide sprays are highly effective chemicals (https://secure.caes.uga.edu/extension/publications/files/pdf/AP%20121-3_1.PDF) . Research shows that keeping populations down early is the key to full-season success.
Rotate effective modes of action (IRAC codes) with each spray.
Use a saltwater rinse to make sure infestations are not getting out of control. Increase
spraying intervals if you are finding large amounts of larvae in samples. See our fact sheet for more info on monitoring SWD using a salt-water rinse.
Picture 1 . Spotted-wing drosophila larvae pictured in a salt-water rinse of harvested blackberry
fruit.
Picture 2. Blackberry fruit beginning to blush (drupelets turning from red to black). This is
the point in which a spray schedule should begin for SWD.
Stink Bugs Stink bugs are often brought up in relation to blackberry, but I would argue that
before 2022 I had rarely stepped into a commercial planting that warranted an insecticide
application for this pest. Almost every field that I’ve been in the last 3 years likely
needed to be sprayed for stink bugs, likely due to the early springs we got each year.
Most growers can achieve suppression through their SWD sprays if the right chemistries
are used when stinkbugs are observed. See below for information regarding how stink
bugs can affect a grower’s bottom line, when control is necessary, and how to get
rid of them.
Stink Bugs and Blackberry Stink bugs are commonly found in blackberry and don’t usually cause too much of a
stink. They do feed on blackberries as seen in the picture below (Picture 3) , but they aren’t after the tasty drupelets like you and me. Dr. Doug Pfeiffer at
Virginia Tech University demonstrated that stink bugs are actually feeding on the
receptacle of the berry, which is the white portion of the berry structure behind
the drupelets. Stink bugs will pierce a drupelet every now and again trying to get
to the receptacle, but that usually isn’t enough to make the berries unmarketable
in local markets. It is not uncommon to find several different species of stink bug
feeding on blackberry such as the adult green stink bug (Chinavia hilaris) in picture 3 , or the immature green stink bugs shown in picture 4 and 5 . We also commonly see brown stink bugs (Euchistus servus), brown marmorated stink
bug (Halymorpha halys), and many leaf footed bug species.
Picture 3. Adult green stink bug (Chinavia hilaris) feeding on a ripe blackberry.
Picture 4 . Immature green stink bug (Chinavia hilaris) feeding on an unripe blackberry.
The Problem with Stink Bugs It’s not hard to find drupelets that have been pierced by stinkbugs but that usually
isn’t too big of a worry. The real issue is that stinkbugs will readily release a
foul-smelling defensive chemical when startled, which will in turn foul the fruit.
Fouled fruit taste just exactly as stink bugs smell, which is not a pleasant experience.
I think everyone reading this who has been unlucky enough to eat one probably remembers
it. Sadly, I have eaten enough stink bug-fouled berries over the last three years
to almost keep me from trying anymore. I say almost because I have a short memory
and I really love fresh blackberries.
The main issue that growers face from large populations of stink bugs is an increased
chance that consumers may have a bad experience. The risk of eating fouled berries
increases at high populations as stink bugs are startled by pickers or others working
in plantings, and also because stink bugs potentially become more easily agitated
when they run afoul of each other often. We’ve seen this in many places where you
can hear bugs buzzing each other and often can smell them in that area. One thing
to note is that leaf-footed bugs do not foul berries and are therefore not a worry
for growers.
Picture 5. Immature green stink bugs (Chinavia hilaris) feeding on unripe blackberry.
How to Manage Stink Bugs in Blackberry In a normal year we tell growers to keep on the lookout for stinkbug egg masses, hatched
out immatures as seen in picture 5 , and a large amount of adults. Currently a threshold doesn’t exist for stink bugs
and it can be hard to gauge what number translates to consumers eating foul berries.
In normal years we see stink bugs very infrequently, maybe 1-2 adults every 50 plants
or so and don’t seem to encounter fouled berries. We normally begin to find issues
when we are seeing stink bugs every few plants or seeing a lot of hatched out immatures
like in picture 5 .
Controlling stink bugs should be fairly simple for blackberry growers. Although we
wouldn’t normally recommend automatic insecticide applications (especially for stink
bugs), in blackberry they are necessary for spotted-wing drosophila. The advantageous
part of this schedule is that many insecticides that work for spotted-wing also do
a pretty good job with stink bugs. Currently growers are utilizing chemistries including
pyrethroids, organophosphates (Malathion), diamides (Exirel), spinetoram (Delegate),
and spinosad (Entrust) for spotted-wing management. Of those insecticide chemistries
listed, growers should only expect reasonable control from pyrethroids which includes
Brigade (bifenthrin), Danitol (fenpropathrin), and Mustang Maxx (zeta-cypermethrin).
Mustang Maxx is most commonly used when blackberries are ripe due to the PHI only
being 1-day, while Brigade and Danitol both have a 3-day PHI.
We currently recommend growers use Brigade (bifenthrin) to clean up stink bugs if
they are observed at high levels pre-harvest, like was observed in picture 5 . If harvest has already started, growers will need to rotate back to a pyrethroid
in their spotted-wing spray schedule when stink bug controls becomes necessary. Growers
that have rotated back to Mustang Maxx in their schedule will see a marked reduction
in stink bug numbers, but keep an eye out for populations that are bouncing back.
In conclusion… I doubt we will ever implement (or develop) a perfect pest management plan for blackberry,
but what we have seen is that implementing cultural tactics, scouting, and hitting
important timings will pay dividends. This year is also a reminder that we must continue
to optimize management plans as the environment seems to become less amenable. In
future years this means more integration of pest prevention and cultural controls,
which research shows helps to mitigate the impact of the environmental curve balls
we will continue to see.
As always, give me a call at 479-249-7352 if you have any questions.
