Parma, Idaho
May 22, 2008
When alfalfa blooms, lygus bugs
take heed. The quarter-inch long pests—with their voracious
appetites for the buds, flowers and seeds of alfalfa—swarm out
of weeds and less-tasty crops and into an alfalfa seed crop
worth about $15 million annually to Idaho growers. Spanning
14,000 acres—most of them in the Treasure Valley—and totaling 10
to 11 million pounds annually, Idaho’s alfalfa seed crop ranks
second in the nation overall and first in the production of
dormant seed for colder climates.
Jim Barbour, a University of
Idaho entomologist who specializes in lygus bugs, calls them
the “scourge of the West” and “the pest problem in alfalfa
seed.” Fields can tolerate five or six lygus bugs per sweep of
an entomologist’s net, “but we can get 50 to 100—and that’s in
areas where we’ve treated.”
Vigorous use of traditional organophosphate and pyrethroid
pesticides—two to eight applications a season—have been
essential to controlling lygus bugs in Idaho’s alfalfa seed
crops. “If growers didn’t treat, they would lose all of their
alfalfa seed,” said Barbour simply. But those older chemicals
also threaten the lives of alfalfa leafcutter bees, which
pollinate Idaho’s alfalfa blooms and trigger the seed production
that puts dollars in growers’ pockets.
Fortunately, trials of “environmentally softer” new chemicals
conducted by Barbour over the past seven years have contributed
to “special local needs” approvals of three products that are
significantly less dangerous to pollinators. While no single new
chemical works as well against lygus bugs as the older
chemicals, Barbour says growers may be able to switch to the
softer chemicals for the four- to six-week period in June and
July when alfalfa leafcutter bees are working blossoms. Using
the new chemicals in combination and enlisting the assistance of
beneficial insects that prey on lygus bugs may prove helpful as
well.
The most recently approved chemical is flonicamid or Beleaf,
which causes lygus bugs to starve by preventing them from
feeding. Another chemical, acetamiprid or Assail, attacks insect
nervous systems, delivering its biggest wallop to insects like
lygus bugs that draw up plant juices through probing parts. A
third chemical, novaluron or RimOn, keeps young lygus bugs from
molting into adults.
“All of these new chemicals are safe to adult bees when applied
according to label instructions,” Barbour said. While adult
leafcutter bees chew circular pieces out of alfalfa leaves for
use in building their nests, they don’t feed on plant parts.
This summer at the University of Idaho’s Southwest Idaho
Research and Extension Center at Parma, Barbour will evaluate
the new chemicals in tank mixes and sequential applications—two
strategies that he hopes will maximize their effectiveness. A
West African graduate student, Tiecoura Traore, will assess the
impact of such beneficial predators as big-eyed bugs, damsel
bugs and minute pirate bugs on lygus bug populations.
“Right now, we don’t know if we can manage lygus bugs with
predators,” said Barbour. “The lygus numbers grow way too
quickly for the predators to keep up with them.” But if the
scientists can pinpoint when the predatory insects should
intervene and what size lygus populations they’re capable of
knocking back, they might be able to manage lygus populations
with the double-barreled strategy of teaming beneficial insects
that aren’t friendly to lygus with chemicals that are friendly
both to beneficial insects and to pollinators.
Founded in 1889, the University of Idaho is the state’s
flagship higher-education institution and its principal graduate
education and research university, bringing insight and
innovation to the state, the nation and the world. University
researchers attract nearly $100 million in research grants and
contracts each year; the University of Idaho is the only
institution in the state to earn the prestigious Carnegie
Foundation ranking for high research activity. The university’s
student population includes first-generation college students
and ethnically diverse scholars. Offering more than 150 degree
options in 10 colleges, the university combines the strengths of
a large university with the intimacy of small learning
communities. |
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