Grapevine moth eradication efforts face uncertainty

Experts agree that the European Grapevine Moth population has
been reduced from last year, thanks to control measures undertaken
by grapegrowers. But just how many moths are still out in vineyards
is impossible to pinpoint.
“We haven’t had any finds in our county,” said Lisa Correia,
Chief Deputy Agricultural Commissioner. “For those people who are
on the ground monitoring, not just the adults, but the larvae is
much harder to find this year. Everything’s pointing really
positively.”
While no European Grapevine Moths have been trapped in Sonoma
County to date, a change in eradication strategy has made the moths
harder to trap.
“It’s the same pheromone in traps as in the mating disruptors,
so it makes it harder for them to find one another, and harder to
find the traps, too,” said Dr. Monica Cooper, Viticulture Farm
Advisor for Napa County University of California Cooperative
Extension.
Mating disruption was not widely used as a control strategy last
year due to a shortage in pheromone supply. This year, use is
widespread. In Napa County, approximately 10,000 acres are under
mating disruption treatment.
“There’s a logistical improvement this year,” said Larry
Hawkins, spokesperson for the USDA. “Last year, there was not
enough of the mating disruption product to go around. That’s not
the case now—the availability is much better this year.”
Last year, traps set in Napa County caught approximately 100,000
male moths. Sonoma County trapped 59. This year, with first
generation peak flight concluded in both counties, Napa County has
caught only 26 moths and Sonoma County has caught zero.
Napa, which first found EGVM in September of 2009, was the
epicenter of last year’s outbreak. Because of the high
concentration of pests, Napa is the only location where the
different stages of the moth can be readily observed in a vineyard
setting. And as it turns out, Napa’s warmer climate is a boon to
eradication efforts in Sonoma County.
“In this first flight, Napa has accumulated more degree days
than Sonoma has, and therefore they are more advanced,” said Rhonda
Smith, viticulture farm advisor for Sonoma County UCCE. “As a
result, we are relying on what Napa sees, and we’re tempering the
timing for our control practices relative to that delay.”
Degree days are commonly used by biologists to predict plant and
animal development, and represent days above the temperature
threshold required for growth.
“There’s a lower threshold of 50 degrees Fahrenheit, and
coincidentally that’s the lower threshold for grapevine
development,” Smith explained.
Dr. Lucia Verela, integrated pest management advisor for UCCE,
is working on developing a degree day model to predict EGVM
development in order to effectively time pesticide applications.
But developing an accurate degree day model takes three years of
data, and this year marks only the second year of the Sonoma County
EGVM invasion.
“What’s really critical at this stage is to have the ability to
monitor what moths are out there in Napa, as well as eggs, larvae,
and feeding damage, with our eyes,” Smith said.
Peak flight in Napa occurred the week of April 18.
Ready-to-hatch eggs known as “black caps” were first noted in Napa
on April 28. Peak egg hatch—the ideal time to spray—is expected to
occur around May 5 and 6 in Napa.
Because of Sonoma’s cooler weather, egg hatch is expected to
begin mid-week. The peak hatch for warm microclimates is expected
to occur the week of May 8, with cooler microclimate delayed even
further.
Staff Writer Lynda Hopkins can be reached at www.hbgtrib.com.