January 2019 - 16

Balancing between pest, pollinator management
By Jacob Pecenka
Purdue University
Insecticides are often needed to
control pests in vegetable crops, but
in crops that require pollinators we
often worry about the impact those
insecticides may have on those
pollinators (Figure 1). In the summer
of 2018, a team of researchers at Purdue
University explored the effects of
insecticide applications on watermelon
yield across Indiana, considering their
impacts on both pests and pollinators.
Using five of the Purdue Agricultural
Centers (PACs), pairs of one-half acre
watermelon plots were planted, each
in the middle of a 15-acre cornfield
(10 total plots) (Figure 2). The two
watermelon plots at each site were
assigned either to a conventional or
an integrated pest management (IPM)
system. The corn surrounding the
conventionally managed watermelons
had a neonicotinoid seed treatment, the
watermelons were given a neonicotinoid
soil drench at transplant, and four or
five pyrethroid sprays were applied
throughout the summer regardless of
pest pressure.
The IPM system had no insecticides
applied to corn or watermelons at planting,
and foliar sprays were only applied when
striped cucumber beetle reached the
economic threshold of five beetles per
plant. Only the IPM plot at the Pinney
PAC (outside Wanatah, Indiana) ever
reached the threshold and received a single
pyrethroid application. The other four IPM
plots received no insecticide applications.
Each pair of watermelon plots
had the same fungicide applications
throughout the summer using Purdue's
MELCAST system (www.melcast.info).
Striped cucumber beetle populations
were higher in the IPM plots than in
the companion conventional plot in all
locations. The yields for the IPM plots
were higher than the conventional plots
Figure 1. Honeybee visiting a male
watermelon flower.
with two plots showing significantly
greater yields.
How can yields be lower in fields
with more applied insecticides and
fewer pests? We believe that the crucial
difference comes from a non-target effect
of insecticides on visiting pollinators.
During five weekly surveys during
peak watermelon flowering, there were
653 pollinators in the IPM plots, as
opposed to just 349 in the conventionally
managed plots. These visitors included
" managed " species such as honeybee and
bumblebees along with numerous native
sweat bees and syrphid flies.
The total number of visits to flowers
and number of pollinating events
(traveling from a male to a female flower)
were recorded for all of the surveyed
insects. The IPM plots had twice as
many total flower visits and three times
as many pollinating events compared
to the conventional watermelon plots.
Since multiple insect visits are required
for watermelon to produce healthy and
marketable fruit, the reduced frequency
of pollination could be leading to the
differences in yield.
These trends show that a " less is more "
approach may be a superior management
strategy when it comes to insecticides
in watermelons and the other vegetable
crops that rely on bees for pollination.
This chart records watermelon weight in 50 m2 subplots at five Purdue Ag Centers (PACs)
with nearest town below. Conventional plots had prophylactic insecticides applied while only
the IPM plot at PPAC reached the economic threshold and received a single spray. The other
four IPM plots never reached thresholds and no insecticides were applied. Source: Purdue
This work was led by entomology
Ph.D. student Jacob Pecenka and he,
along with other members of the team
will continue to look at these trends
for the next few years, examining
the effects that insecticides have on
managed pollinators like honeybees
or bumblebees that are often found
near cucurbits. The goal is to provide
guidelines for growers who want to
employ more sustainable management
practices in their farming operations.
It seems that a return to an old, and
often neglected practice - IPM - may
offer a solution.
If you have questions or would like to
learn more contact at jpecenka@purdue.
edu or check out the project's website
for updates and information: www.
pollinatorprotection.org. VGN
Figure 2. Example of research plot design; half-acres of watermelons within a 15-acre
cornfield.
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January 2019

Table of Contents for the Digital Edition of January 2019

January 2019 - 1
January 2019 - 2
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