A34-Lancaster Farming, Saturday, April 21,2001
CONDUCTING AN
ON-FARM TEST
John Rowehl, CCA
Cumberland County Agent
Many farmers like to conduct
tests of hybrids, varieties, crop
protection chemicals, or other
crop inputs on their own fields.
Done correctly, this is a good
thing to do. If not done the right
way, results may be misleading.
The most important thing to
keep in mind is that you want to
remove as many confounding
factors as possible from any test
you do on your farm. A common
mistake is making a comparison
between one year and another or
between one field and another
with different soils, soil fertility,
different crop history, etc.
Doing a side-by-side compari
son is the best approach to take.
This removes influences of time,
planting and harvesting condi
tions, cropping history, and
weather changes.
Try to use a field with soils as
uniform as possible. But varia
tions in soil type and soil fertility
exist in even the best fields and
must be taken into consideration.
Anyone who has seen a yield
map or had grid soil sampling
has seen this.
There are two different ap
proaches to dealing with this.
One popular way, particularly in
hybrid testing, is to use a multi-
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pie check system in which a
“tester” hybrid is planted every
third or fourth strip. This check
is used to adjust the yields of the
other hybrids to compensate for
changes in the field.
The other way and preferred
method of crop scientists is to
replicate the treatments several
times in the field. By not doing
one of these things, there is a
good chance that the results you
see are due to the differences in
the field rather than differences
in the products themselves.
Look at the following example
of two hybrids that were tested
last year in an on farm test. The
yields shown are from each repli
cation. Look at any single repli
cation and ask yourself what
conclusion you would come to if
only one side-by-side test had
been done. Then look at another
replication and ask yourself the
same question.
Bu/Ac
Hybrid Rep 1 Rep 2 Rep 3
A 173 208 186
B 181 186 203
(The average of these two hybrids can be found at the
end of this article).
In some areas, several fanners Hybrid A = 189 bushels per
work together to do the same acre.
comparisons on several farms in Hydrid B = 190 bushels per
the area. The advantage of this is acre.
Ohio State Pathologist
Plant Pathogen Test
Improves
WOOSTER, Ohio A test
commonly used to detect the
presence of a plant pathogen in
the aster leafhopper has been im-
that it reduces the number of
replications needed on any one
farm.
Make the width of each treat
ment as narrow as possible so
that the variation in soil change
is as small as possible. Likewise,
keep the number of things you
are trying to compare to a min
imum for the same reason. Try to
use a field that’s at least several
hundred feet long to help dilute
the effects of extra good or poor
spots in the field or from the ef
fect of a planter or spreader not
operating normally at the end or
beginning of a field as it starts
up.
An informational circular
about conducting on farm tests is
available from cooperative exten
sion. If you are interested in
doing a test of your own, you can
always contact one of the agron
omy agents to bounce some ideas
off of us.
RABIES VACCINATION FOR POOS
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DATE: Saturday, April 20th, 2001
WHERE: Ooodville Fire Hall, Rte. 23 in Ooodville east of Blue Ball
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TIME: 9:00 AM - 3:00 PM
COST: $9 per dog
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proved to further differentiate in
sects that are likely to spread the
pathogen from plant to plant
from those insects that are just
merely infected.
The aster leafhopper, an insect
that feeds on such crops as let
tuce, carrots and celery, is a vec
tor for aster yellows phytoplas
ma, a pathogen that can cause
severe economic losses of the
crops, especially lettuce. Dis
eased plants turn yellow, are
malformed and may bolt prema
turely, making them unmarket
able. Aster yellows phytoplasma,
a cell wall-less bacterium that
causes the aster yellows disease,
cannot be cultured in the lab and
is difficult to detect in the field.
Ohio State University plant
pathologist Sally Miller said spe
cifically identifying the reproduc
tive status of the pathogen within
the leafhopper may help predict
seasonal epidemics leading to ef
fective preventive methods of
control. Miller works at the uni
versity’s Ohio Agricultural Re
search and Development Center
in Wooster.
The most common method for
detecting aster yellows phyto
plasma involves a polymerase
chain reaction assay (PCR) that
amplifies specific fragments of
phytoplasma DNA in the leaf
hopper. The test, though quick
and highly effective, only detects
the presence of the pathogen and
does not differentiate between in
sects that are infected and those
that are inoculative, or able to
transmit the pathogen from
plant to plant. Miller and
OARDC graduate student J.H.
Zhang developed a sucrose-feed-
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ing solution method preceding
the PCR assay that screens for
those differences.
“The PCR assay is good for
detecting the pathogen. But the
feeding solution method goes one
step further in determining
whether or not a leafhopper can
transmit it to plants,” said Mill
er. “From those results we can
predict aster yellows epidemics
and recommend to farmers cer
tain preventive or control mea
sures.”
The idea behind the technique
involves feeding infected leaf
hoppers a sucrose solution
through a parafilm membrane.
While feeding, leafhoppers with
a high phytoplasma content will
spit the pathogen into the solu
tion. Leafhoppers that do not
carry the phytoplasma, or those
in which the phytoplasma’s dor
mant period is not complete, do
not return the pathogen to the
feeding solution. The solution is
then tested by PCR.
“From the test, we can esti
mate how many insects are inoc
ulative and how many are only
infected, and not yet inocula
tive,” said Miller. The study con
ducted to determine the accuracy
of the sucrose solution showed
that the method could positively
detect inoculative insects over 99
percent of the time.
The sucrose-feeding technique
is part of a larger research proj
ect being conducted by OARDC
scientists using simulation mod
els and a geographic information
system to map out aster leafhop
per populations to track the
spread of aster yellows through
out lettuce fields in northern
Ohio.
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