Agriculture Reference
In-Depth Information
weapons of war, to use against insects. Scientists and growers discovered
they could use one organophosphate—azinphosmethyl (Guthion)—with
their pear IPM strategies. By spraying it conservatively and precisely,
growers managed their codling moth populations until 1991, when it
stopped working. They applied the maximum legal rate—four sprays of
3 pounds of Guthion per acre—and still failed to stop the pest from
eating into Hemly's income. When azinphosmethyl lost its efficacy
against the codling moth, Weddle knew they had a problem. He con-
tacted Stephen Welter, a professor and researcher at the UC Berkeley
entomology department specializing in plant-insect interactions and the
management of insect populations in agroecosystems. Weddle himself
had received an MS degree from that department, inspired by
Silent
Spring
and attracted to the ecologically informed initiatives undertaken
by its faculty. Welter and his graduate student John Dunley devised a
new methodology to assess resistance. They confirmed that codling moth
populations in the Sacramento River pear district were now effectively
immune to this pesticide.
2
Fortunately, some Australian scientists had developed a novel product
that releases a chemical mimicking the sex pheromones female codling
moth release to attract the male for mating. Isomate dispensers appear
like plastic twist-ties, and over a period of months they release their
0.0028 fluid ounce of synthetically produced pheromone into
the orchard air, frustrating mating. In theory, flooding the orchard with
artificial pheromones could disrupt the pest's reproductive cycle, but no
one had ever done this in a commercial orchard. Because mating disrup-
tion is not lethal to insects, it would have to be deployed fully and
consistently throughout the orchard when the codling moth is in flight.
A failure to completely blanket the orchard with pheromones could
result in an economic disaster.
Weddle had experimented with an earlier pheromone product on one
orchard block, but used the regular organophosphate application to kill
any additional codling moths that flew in from adjacent orchards. This
proved effective, but at twice the cost. Weddle had more than 20 years
of applied IPM experience, but the technical skills this experiment
required were daunting. Welter thought the product could work, but
only if the entire contiguous block of pear trees were managed to disrupt
codling moth mating. He agreed to work on the project, but only on the