May 2021 - 5

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FGN | MAY 2021 | 5
C
oncerned that rainfall
could increase the chance
of pests damaging
your tree fruit, even though
you recently treated with an
insecticide?
How well your insecticide fares
during a rain depends both on
how much precipitation occurs
and the active ingredient's
susceptibility to wash-off,
according to recent Michigan
State University studies.
The studies rated the rainfast
qualities of several active
insecticide ingredients on apples
and tart cherries. Results show in
general that organophosphates
are the most sensitive to wash-off,
whereas spinosyns, pyrethroids
and diamides are more rainfast.
Neonicotinoid surface residues
are sensitive to wash-off, but
subsurface residues are not.
The studies show that
several compounds, including
spinetoram, the active ingredient
in Delegate®
WG insecticide,
continue to provide plant
protection despite rain showers.
Rainfall of less than one-half
inch caused little, if any, product
loss from fruit or leaf tissue,
says John Wise, Michigan State
University entomologist.
Studying insecticides used in
apples and tart cherries, Wise
analyzed fruit and leaf tissue to
determine insecticide loss due to
rainfall.
Apples treated with
Delegate®
WG insecticide,
a spinosyn, had negligible
loss with less than 1 inch of
precipitation.
In the study, a product loss
of 30% or less was considered
highly rainfast. A moderately
rainfast rating was given if
product loss remained below
50% and a product loss of 70%
was given a low rainfast rating.
Overall, Delegate applied to
fruit and leaf tissue was rated
highly rainfast to a half-inch or
less of rain. When rain totaled
1 inch, Delegate was rated as
highly rainfast on fruit tissue
and moderately rainfast on leaf
tissue. Even with a 2-inch rainfall,
Delegate maintained a moderate
rainfast rating on fruit tissue.
" This is commonly seen with
Is Your Pest Protection
Washing Away?
Delegate® WG Insecticide Performs Well in Michigan Rainfast Studies
spinosyns that tend to be more
rainfast on fruit tissue than leaf
tissue. With 1 inch of rain, which
is a substantial rainfall, there
was minimal product loss on
fruit tissue, " says Wise, who
presented his findings at the
2021 Mid-Atlantic Fruit and
Vegetable Conference.
Wise's bioassay studies also
found a significant effect of
rainfall wash-off only when
precipitation surpassed 1 inch.
He attributes the continued
pest protection to the binding
affinity of spinosads (Delegate)
to fruit tissue.
A second tart cherry study
with spotted wing drosophila
demonstrates a similar rainfast
pattern.
" With spinetoram or Delegate,
there's sensitivity to wash-off on
leaf tissue at the higher rainfall
amounts, but not so much on the
fruit tissue, " Wise says. " There
was a statistical loss in protection
at the higher rainfall levels, but
not as dramatic as some of the
other compounds we tested. That
matches the rainfast data we saw
in the apple study. The product is
persisting on the fruit. "
Bioassay data reveals
significantly more spotted wing
drosophila larvae collected per
cherry in the untreated check,
no matter the precipitation
amount. Significantly fewer
larvae were documented in the
trial for Delegate.
" Left untreated, spotted wing
drosophila larvae didn't care if
there was simulated rain or not.
We collected at least 30 to 40
larvae per fruit whether there
was zero, half inch or 1 inch of
rainfall, " Wise says.
Wise also examined the
potential differences between a
1-inch rain falling in an hour or
a day.
" We varied that factor in a
number of studies using the
university's rainfall simulation
chamber and did residue
analysis, " he says. " We did not
find that the intensity or the
duration of the rainfall event
had a major effect on product
wash-off. "
He also looked at the role of
surfactants in insecticide wash-off.
" Many surfactants improve the
end result of residue remaining
after a precipitation event, but
the data suggests that it is not
necessarily that the surfactant
directly inhibited wash-off.
In many cases, it may simply
increase the deposition because
the surfactant treatment began
with a lot more residue than the
comparison without surfactant, "
he says.
Contact your local Corteva
Agriscience representative or visit
DelegateWG.Corteva.US to learn
more about how Delegate®
WG
insecticide can protect your
fruit crop against yield-robbing
pests.

http://www.FruitGrowersNews.com http://DelegateWG.Corteva.US

May 2021

Table of Contents for the Digital Edition of May 2021