Computer Tool Provides New Methods Of Plant Disease Control
WOOSTER, Ohio A
computer model linking sim
ulation techniques with a
geographic information
system (GIS) is providing
vegetable farmers with new
strategies for controlling a se
rious plant disease carried by
insects.
The epidemiological
model, developed by Ohio
State University researchers,
combines GIS technology
with a mathematical repre
sentation of insect and plant
populations, to map out the
movements of aster leaf
hoppers among lettuce fields.
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Such a tool enables the re
searchers to track the spread
of aster yellows, a disease
carried by the aster leaf
hopper, that can cause severe
economic losses to such crops
as lettuce, carrots, and celery.
Casey Hoy, an Ohio Agri
cultural Research and Devel
opment Center entomologist
and the project leader, said
that since the aster leaf
hopper is responsible for
spreading aster yellows from
plant to plant, it’s important
to understand the movement
of the insect as a means for
controlling the spread of the
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disease.
“With the model, we can
predict where the leaf
hoppers will go, how many
wind up in each field, and
whether they are healthy or
infected with the disease.
Such information allows us to
recommend to farmers better
timing on when to spray their
fields,” said Hoy, adding that
farmers will frequently spray
whether the disease is present
or not. “This model also is al
lowing researchers and farm
ers to evaluate alternative
control methods to using in
secticide.”
The researchers studied
population movements of the
insect in lettuce fields near
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by capturing thousands of
them, marking them with flu
orescent paint, releasing
them at a single point, and
then recapturing them 24
hours later. Using the pattern
of leafhopper movement and
such variables as field shape
and spatial patterns, time
and location of insecticide
applications, the number of
immigrating leafhoppers,
and wind direction, the re
searchers were able to predict
aster yellows epidemics for
an entire growing season.
“One thing we found was
that keeping fields separated
from each other by 60 meters
cut down a lot on leafhopper
dispersal rates from field to
field,” said Hoy. The study
predicted a 22 percent reduc-
tion in aster yellows inci
dence when such a distance
separated the fields.
The study also pointed to
the crucial timing involved in
the harvest. “The percentage
of the crop showing symp
toms at harvest depends on
how long it takes for the leaf
hoppers to get in and infect
the crop,” said Hoy. “If
farmers plant a crop that will
mature faster or that will ex
press symptoms more slowly,
we predict a significant de
crease in the disease and in
the need to spray for the leaf
hoppers.”
Hoy said aster yellows has
the potential to wipe out 100
percent of a lettuce crop. The
disease causes the crop to
turn yellow, making it un
marketable, and eventually
die.
Other OSU researchers in
volved in the project include
OARDC Associate Director
L.R. “Skip” Nault and
OARDC Plant Pathologist
Sally Miller. Funding for the
project was supported by
grants from the U.S. Depart
ment of Agriculture Cooper
ative State Research,
Education and Extensive
Service (CSREES) North
Central Region Integrated
Pest Management Grants
Program, the USDA
CSREES National Research
Initiative Assessing Pest
Control Strategies Program,
and the Ohio Small Fruit and
Vegetable Research Founda
tion.
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