March 2019 - 32

Caging orchards viewed as a method to protect apples
By USDA Western IPM Center
When brown marmorated stink bugs
hit the Mid-Atlantic region, they wreaked
havoc with the tree fruit industry. Growers
were forced to abandon effective integrated
pest management programs and resort
to frequent sprays of broad-spectrum
insecticides to protect their crops.
Elizabeth Beers and her colleagues
at Washington State University are
working to make sure that doesn't
happen again in Washington's valuable
apple and pear orchards.
Beers, stationed at the university's
Wenatchee Tree Fruit Research and
Extension Center, is investigating whether
IPM tactics - specifically exclusion and
biological control - can keep the voracious
invasive insect at bay.
" The brown marmorated stink bug
Apple trees inside a shade-netting enclosure. Photos: USDA
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is still in the process of invading our
state, " she said. " About half the counties
in Washington have had a confirmed
detection, and growers are on the threshold
of where they're getting damage. Based on
what happened the eastern U.S., that's going
to get steadily worse. "
To prevent that, Beers and her graduate
students, Adrian Marshall, Joshua Milnes
and Jim Hepler, are testing whether the
shade netting growers already use to protect
their apples from sunburn can also protect
it from stink bugs.
" We're looking at physical exclusion, "
Beers said. " Literally putting the trees in
a cage. "
The idea isn't as crazy as it sounds. As
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apple orchards increasingly move toward
high-density, trellised plantings, the fruit is
less shaded by foliage and more susceptible
to sunburn, so growers are increasingly
encasing large swaths of apples in netting
that provides 20 percent shade. The
openings in that netting are about 2 by 5
millimeters.
" Will that netting exclude stink bugs? "
Beers asked. " Will it exclude other direct
pests, like codling moth, because you can
never have too many controls for codling
moth. And are there unintended effects of
the netting? "
The team already has answers to some
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of those questions, and yes, there are
unintended effects. While the netting
does seem to keep the stink bugs out (and
help a little with codling moth) it also
keeps out beneficial insects that control
other pest species.
" We're seeing outbreaks of secondary
pests, like woolly apple aphid, due to the
exclusion of natural enemies, " she said.
The team is trying to introduce natural
enemies into the enclosures, but haven't
have much success yet. They are also testing
insecticide-infused netting, which works
very well but indiscriminately, and testing
a variation of exclusion tactics that puts a
barrier between natural vegetation where
the stink bugs come from and the orchards.
Beers and her colleagues are building big
bug walls.
" What I like about the idea is that it
m
a
32 | FruitGrowersNews.com
uses the behavior of the insect to target
it, " she explained. " Some insects may just
fly around a barrier. We believe stink
bugs, when they fly into something, they
Elizabeth Beers in an experimental apple
cage.
Native parasitic wasps don't much care
to attack brown marmorated stink bug
eggs, but several Asian species do. Some of
those species are being tested in quarantine
to see if they are exclusive or preferential
parasitoids of the brown marmorated stink
bugs or if they'll also attack native stink
bugs, some of which are beneficial.
But that research is in quarantine
laboratory conditions, so in Washington,
researchers are looking at the parasitic
wasps in the wild.
" It's not a species-specific parasitoid,
but it clearly shows a preference for brown
marmorated stink bugs, " Beers said. " And all
the native species we've tested it against are
all pests, too. "
Beers believes there won't be a silver
bullet to managing the brown marmorated
stink bugs - or codling moth, or spottedwing
drosophila, or pear psylla, or any of
the other pests they study at the Wenatchee
Tree Fruit Research and Extension Center.
Instead, classic integrated pest management
will continue to provide the best option for
long-term pest control that protects crops,
consumers and the environment.
" Unfortunately, when you go through an
invasion, the first priority is control damage
by any means possible, " she said. " And that's
usually broad-spectrum insecticides that
are unfriendly to IPM. We want to avoid
that and find IPM solutions to these pest
challenges. " FGN
cling to it then crawl up to get over it. " So
researchers are sewing flaps into the net
wall that traps stink bugs as they make that
climb, and looking at lining those pockets
with the insecticide-infused netting to make
the traps even more effective.
Both full enclosures and the orchard
border walls have been tested for one season
but it was a low-pressure year for stink bugs
so their effectiveness was hard to measure.
(One thing the team did learn was that
successfully erecting a 12-foot-tall screen
wall in a windy environment requires
engineering and construction expertise not
typically found in research entomologists.)
Unleash the parasitic wasps
" I think the long-term solution to
suppressing brown marmorated stink bug
will be biological control, " Beers said. " A
survey looking for parasitoids of brown
marmorated stink bug in 2015 detected
the samurai wasp, (Trissolcus japonicus),
an exotic egg parasitoid in Vancouver,
Washington. Since then, there's been
more surveys and more detections in
Washington and around the U.S. "
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http://www.orchard-rite.com http://www.FruitGrowersNews.com
March 2019

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