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CORN
Crop Observation and Recommendation Network
August 28 - September 4, 2000
C.O.R.N. 2000-28
In This Issue:
A) Yellowing Between theVeins of Soybean Leaves is Not a Reliable
Symptom for Diagnosis!
B) Estimating Grain Yields in Corn Prior to Harvest
Several soybean samples were received this last week in
which the leaves had
yellow spots with some leaves turning brown or necrotic between the veins.
There were few roots on these plants and absolutely no secondary roots. The
piths were entirely degraded and if you squeezed the top of the plant with
your fingers the stems collapse. Additionally, the Rhizobium nodules were
dead, many of them empty. Also the roots had no epidermis, or if present
you could easily pull it off. When you cut open the crown it is dull
brown-gray in color throughout. This is flooding - saturated soil injury.
These foliar symptoms are very similar to Sudden Death Syndrome and Brown
Stem Rot but we have not been able to isolate either of the pathogens that
cause these two diseases from these plants. In both Sudden Death Syndrome
and Brown Stem Rot, the soybean's pith is intact. For Sudden Death, the
pith is still white; and with Brown Stem Rot it is a distinct chocolate
brown color. Sudden Death Syndrome is a good root rotter and the crowns
will be colonized, but in most cases we can see distinct areas of healthy
vs. diseased tissue. The root epidermis is intact and can't be pulled off.
With both of these diseases the Rhizobium nodules are healthy.
This is a real challenge to diagnose, but flooding injury does occur in
those areas of the fields where the water sits for extended periods of time.
One of the samples that was sent in came from an area of the field in which
green algae (green scum) could be found on the soil surface! If flooding
injury is the problem, then those are areas of a field in which drainage
needs to be improved.
If it is a disease that your soybeans have, again improving drainage, and
choosing soybean varieties with resistance is the way to go. Don't forget
SCN, it can also cause early yellowing at this time of year.
Two procedures which
are widely used for estimating corn grain yields prior
to harvest are the YIELD COMPONENT METHOD (also referred to as the "slide
rule" or corn yield calculator) and the EAR WEIGHT METHOD. Each method will
often produce yield estimates that are within 20 bu/ac of actual yield.
Such estimates can be helpful for general planning purposes.
THE YIELD COMPONENT METHOD was developed by the Agricultural Engineering
Department at the University of Illinois. The principle advantage to this
method is that it can be used as early as the milk stage of kernel
development. The yield component method involves use of a numerical
constant for kernel weight which is figured into an equation in order to
calculate grain yield. This numerical constant is sometimes referred to as
a "fudge-factor" since it is based on a predetermined average kernel weight.
Since weight per kernel will vary depending on hybrid and environment, the
yield component method should be used only to estimate relative grain
yields, i.e. "ballpark" grain yields.
When below normal rainfall occurs during grain fill (resulting in low kernel
weights), the yield component method will OVERESTIMATE yields. In a year
with good grain fill conditions (resulting in high kernel weights) the
method will underestimate grain yields.
Step 1. Count the number of harvestable ears in a length of row equivalent
to 1/1000th acre. For 30-inch rows, this would be 17 ft. 5 in.
Step 2. On every fifth ear, count the number of kernel rows per ear and
determine the average.
Step 3. On each of these ears count the number of kernels per row and
determine the average. (Do not count kernels on either the butt or tip of
the ear that are less than half the size of normal size kernels.)
Step 4. Yield (bushels per acre) equals (ear #) x (avg. row #) x (avg.
kernel #) divided by 90.
Step 5. Repeat the procedure for at least four additional sites across the
field.
Example: You are evaluating a field with 30-inch rows. You counted 24 ears
(per 17' 5" = row section). Sampling every fifth ear resulted in an average
row number of 16 and an average number of kernels per row of 30. The
estimated yield for that site in the field would be (24 x 16 x 30) divided
by 90, which equals 128 bu/acre.
THE EAR WEIGHT METHOD can only be used after the grain is physiologically
mature (black layer), which occurs at about 30-35% grain moisture. Since
this method is based on actual ear weight, it should be somewhat more
accurate than the yield component method above. However, there still is a
fudge factor in the formula to account for average shellout percentage.
Sample several sites in the field. At each site, measure off a length of
row equal to 1/1000th acre. Count the number of harvestable ears in the
1/1000th acre.
Weigh every fifth ear and calculate the average ear weight (pounds) for the
site. Hand shell the same ears, mix the grain well, and determine an
average percent grain moisture with a portable moisture tester.
Calculate estimated grain yield as follows:
Step A) Multiply ear number by average ear weight.
Step B) Multiply average grain moisture by 1.411.
Step C) Add 46.2 to the result from step B.
Step D) Divide the result from step A by the result from step C.
Step E) Multiply the result from step D by 1,000.
Example: You are evaluating a field with 30-inch rows. You counted 24 ears
(per 17 ft. 5 in. section). Sampling every fifth ear resulted in an average
ear weight of 1/2 pound. The average grain moisture was 30 percent.
Estimated yield would be [(24 x 0.5) / ((1.411 x 30) + 46.2)] x 1,000, which
equals 135 bu/acre.
Because it can be used at a relatively early stage of kernel development,
the Yield Component Method may be of greater assistance to farmers trying to
make a decision about whether to harvest their corn for grain or silage. If
stress conditions, such as drought, have resulted in poorly filled small
ears, there may be mechanical difficulties with sheller or picker efficiency
which need to be considered. Since it will probably be cheaper to buy corn
for grain than to buy hay for roughage (because of the likely forage
deficit), there will be greater benefit in harvesting fields with marginal
corn grain yield potential for silage.
Readers can subscribe electronically to this newsletter by sending an e-mail
message to: corn-out-on@postoffice.ag.ohio-state.edu.
A successful subscription message will receive by an automatic reply from the
listserv. Contact your local Ohio State University Extension Office or e-mail labarge.1@osu.edu
if you have problems subscribing.
Past versions of C.O.R.N. can be found on the World Wide Web at: http:/www.ag.ohio-state.edu/~corn/archive/
C.O.R.N. is a summary of crop observations, related information, and appropriate
recommendations for Ohio Crop Producers and Industry. C.O.R.N. is produced by
the Ohio State University Extension Agronomy Team, State Specialists at The
Ohio State University and Ohio Agricultural Research and Development Center.
C.O.R.N. Questions are directed to State Specialists, Extension Associates,
and Agents associated with Ohio State University Extension and the Ohio Agricultural
Research and Development Center at The Ohio State University.
Contributors to C.O.R.N. this week include:
State Specialists: Bruce Eisley (Entomology), Ron Hammond (Entomology), Pat
Lipps (Plant Pathology), Anne Dorrance (Plant Pathology), Erick DeWolf
(Plant Pathology), Jeff Stachler (Weed Science), Peter Thomison (Corn
Production); Extension Agents: Steve Prochaska (Crawford), Clark Hutson (Seneca),
Gary
Wilson (Hancock), Roger Bender (Shelby), Greg LaBarge (Fulton), Barry Ward
(Champaign), Dave Jones (Allen), and Andy Kleinschmidt (Van Wert).
Editor: Andy Kleinschmidt
Web Editor: Tom Rosati
Information presented above and where trade names are used,
they are supplied with the understanding that no discrimination is intended
and no endorsement by Ohio State University Extension is implied. Although every
attempt is made to produce information that is complete, timely, and accurate,
the pesticide user bears responsibility of consulting the pesticide label and
adhering to those directions.
All educational programs conducted by Ohio State University
Extension are available to clientele on a nondiscriminatory basis without regard
to race, color, creed, religion, sexual orientation, national origin, gender,
age, disability or Vietnam-era veteran status.
Issued in furtherance of Cooperative Extension work, Acts of
May 8 and June 30, 1914, in cooperation with the U.S. Department of Agriculture,
Keith L. Smith, Director, Ohio State University Extension.
TDD # 1 (800) 589-8292 (Ohio only) or (614) 292-1868
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