From Jason Kolln, Your Pioneer Agronomy and Product Specialist.
August 2011
HIGH TEMPERATURES CAUSING SOME PARTIALLY-FILLED EARS?
Many growers experienced tip-back in 2010 corn fields. In many areas, corn
fields are showing tip-back again in 2011. Tip-back has several causes. Excessively warm weather during grain-fill can cause corn ears to “tip back”. High
nighttime temperatures cause plants to expend unnecessary energy
(carbohydrate) to maintain plant functions. Those carbohydrates would normally be moved to the ear for storage. Sensing the lack of energy available,
the plant responds by reducing the number of kernels it will attempt to fill.
Roger Elmore, with ISU Extension, documented that the higher than normal
nighttime temperatures of 2010 resulted in approximately a 10% yield reduction in last season’s corn crop. Purdue University agronomist, Dr. Bob Nielsen,
suggests that “kernels are most susceptible to abortion during the first 2 weeks following pollination, particularly kernels near the tip of the ear”. Tip kernels are generally last to be fertilized, are less vigorous than the
other kernels, and are most susceptible to abortion.
During pollination this year and in the two weeks post-pollination Central Iowa experienced many subsequent
days of temperatures in the mid 90’s with nighttime lows near 70 degrees, thirty year nighttime temperatures
trend in the low 60’s. After successful pollination of 40-45 kernels in length, many ears have aborted back to a
length of 30-32 kernels.
Hybrid differences are explained by: timing of stress relative to pollination, silking dates, genetic tolerance to
stress and the hybrid’s tendency to adjust ear length. Field to field variation within the same hybrid can also
exist due to subtle differences in environmental stress.
Once kernels have reached the dough stage of development, further yield losses can occur mainly from reductions in kernel dry weight accumulation and overall kernel size.
Remember to focus NOT on how many kernels have tipped back, rather the remaining kernels on the ear.
Overall yield levels will still be very good, but we did take the top off of what was on track to be a record
breaking harvest in NC Iowa.
TIMING OF STRESS AFFECTS YIELD:
The interaction between stage of development and crop stress plays a critical role in corn yield determination.
Stress during various stages will affect grain yield as noted below:
BLISTER (R2) 40-50 days to maturity: kernels are white and resemble a blister. Relocation of plant nutrients
from vegetative growth to ear fill has begun. Severe stress at this time can easily cause kernels to abort. Kernel abortion starts at the ear tip.
MILK (R3) 35-42 days to maturity: kernels are nearly all yellow and contain a milky-white fluid. This is the
"roasting ear" stage. Severe stress can still abort kernels, as well as, reduce kernel weight.
DOUGH (R4) 30-36 days to maturity: Continued starch accumulation is giving the kernels' inner fluid a pasty
consistency. Kernel abortion is not very likely, but severe stress can have a dramatic impact on test weight.
DENT (R5) 20-27 days to maturity: Nearly all of the kernels are dented. The milk line slowly progresses to the
kernel tip over the next 3 weeks. Kernel moisture at the beginning of the R5 stage is approximately 55%.
When the kernel reaches ½ milk line, it will be roughly 40% moisture, 14 days from black layer, and have attained about 95% of its maximum yield. Stress at this stage can still reduce kernel weight.
MATURITY (R6): The black layer has formed and kernels have attained maximum dry weight. Kernel moisture is roughly 30 to 35%. Stress at this point will not reduce final yield unless the stress results in physical
grain loss (e.g. ear drop, severe stalk rot).
CORN YIELD ESTIMATES:
Corn yield estimates can be made by using the Yield Component Method
developed by the University of Illinois several years ago. The Yield Component Method can be used well ahead of harvest when kernel development
has reached the late milk to early dough stages (R3-R4) or about 25 days
after pollination. The Yield Component Method uses the number of ears
per 1/1000th of an acre and the number of kernels per ear to calculate an
estimate of yield. This estimate of yield is certainly not 100% accurate and
crop uniformity greatly influences the accuracy of yield estimations.
Additional samples are needed to more accurately estimate yields as field variability increases. To get a
“ballpark” estimate of your corn’s yield, follow these steps:
1. Measure off the length in your corn rows equal to 1/1000th of an acre. (20” rows = 26’2”, 30” rows = 17’5”,
6” rows = 14’6”)
2. Count and record the number of harvestable ears in the 1/1000th acre.
3. For every fifth ear in the 1/1000th acre of a row, count the number of complete kernel rows per ear. Do
not sample nubbin or odd ears unless they represent the sample area. Calculate and record the
average number of kernels per row.
4. Using the same ears, determine the number of kernels per row on each ear. Do not count the smaller
kernels on the ear tip. Calculate and record the average kernels number per row for all ears sampled.
5. Estimate the yield for each site by multiplying the ear number x average row number x average
kernels/row, and then divide that result by 90. The value of 90 represents the average number of kernels (90,000) in a bushel of corn. For high test weight Pioneer hybrids, using 80,000 kernels per bushel of
corn may be more accurate.
Example: You counted 28 harvestable ears and when you sampled every 5th ear, you averaged 16 rows around the ear with 40 kernels/row. The estimated yield would be 28 x 16 x
40 divided by 90 = 199 bu./A.
PERCENTAGE OF MAXIMUM YIELD BY GRAIN FILL STAGE:
CORN
LEFT UNTIL MATURITY
% of MAXIMUM YIELD
% MOISTURE
Stage
Days
GDUs
Grain
Plant
Grain
Plant
Late Milk
30-40
700
30-50
65-75
60-80
75-80
Early Dent
20-25
425-525
60-75
75-85
50-55
70-75
1/2 Milk Line
10-15
200-300
90-95
100
35-40
65-70
Black Layer
0
0
100
95-100
28-30
55-65
GOSS’S BACTERIAL WILT IN CORN:
We continue to find and confirm many cases across Iowa of
Goss’ Wilt. In Central Iowa the most severe instances are isolated to corn on corn fields planted to susceptible hybrids. Lesions can also be found to a lesser extent in rotational fields.
Goss’s Wilt lesions are large, have wavy margins and are brown,
yellow, and gray in color. They may be elliptical or V-shaped and
usually extend down a leaf vein. The tissue neighboring the lesion is water soaked. It is common for the bacteria that cause
this disease to ooze out onto the leaf surface, so the lesions often have a shiny appearance. Most characteristic though, are the
dark green “freckles” that occur within the lesion.
Goss’s Wilt disease can progress rapidly under the right conditions (warm 80 degree F and wet) resulting in
extensive leaf blight and death of the canopy. Since this is a bacterial disease, a fungicide application will not
control the disease. The pathogen is able to survive in infested surface crop residue for 10 months. The recommended management practices include rotation to a non-host crop, any type of tillage that buries the infested residue and helps with decomposition, and tolerant hybrids. Refer to the July issue of WYF for more
details on this disease.
WATCH FOR STALK ROTS IN CORN THIS FALL:
Anything that inhibits photosynthesis can create a higher likelihood of reduced stalk integrity as photosynthates are directed to the ear, more so than the stalk and roots, during the reproductive stages of corn. This
can lead to a shortage of photosynthates in the stalk, which in turn, may lead to stalk rots. The early portion
of the grainfill period has certainly caused some concerns with reduced photosynthate availability due to
warmer temperatures driving respiration rates at a faster pace. As the rest of the fall progresses, suspect
fields should be closely monitored for stalk quality. A quick way to test stalk strength is to walk down the row
and push stalks until tassels touch the adjacent row. If stalk rots are present you will feel the stalk “crimp” below the ear.
There are several different stalk rots that may infect corn fields. The most common are Gibberella, Diplodia,
Fusarium and Anthracnose. Symptoms of Gibberella, Diplodia, and Fusarium can often be confused. These
three diseases cause disintegration of the pith tissue, leaving the vascular bundles intact, so the interior of the
stalk has a shredded appearance. The pith also will be discolored and the color of the pith may help with diagnosis. It can be really difficult to determine the type of stalk rot based on visual symptoms, so I encourage
the use of the lab for positive identification of diseases. Checking fields early and regularly by pinching or
pushing stalks can help prioritize harvest and minimize the yield loss that can be associated with harvest
challenges due to stalk rots.
Anthracnose Stalk Rot
Symptoms of anthracnose are fairly easy to recognize and usually are not confused with other stalk rot diseases. Late in the
season shiny black, linear streaks and blotches appear on the
surface of the lower stalk above the brace roots. Occasionally,
the entire stalk becomes blackened. The internal stalk tissue or
pith becomes discolored, turning dark gray to brown and shredded. The picture to the right is a great example of anthracnose
stalk rot.
Diplodia Stalk Rot
Symptoms may be similar to those of Gibberella stalk rot, but Diplodia doesn't develop a pink color in the pith of the stalk. White mycelium can develop in lower stalks and you may see tiny black specks
(pycnidia) embedded in the rind of the lower stalk. The lower inner
stalk may have shredded tissue and pycnidia may also be present.
The first picture to the right shows the pycnidia on the external stalk
and the far right picture shows the white mycelium that is developing
in the inner stalk.
Fusarium Stalk Rot
Fusarium stalk rot is very similar to Diplodia and Gibberella stalk
rots. The inner stalks will typically have a light pink discoloration but
will lack black specks or pycnidia may be present in the stalks that
are infested with Diplodia. A white to salmon pink colored growth is
evident on vascular strands when spores are produced. There may
also be a reddish-pink discoloration of the roots. Unlike Diplodia,
there will not be any pycnidia on the outer stalk. Stalks that have
Fusarium may have brown streaks on the internodes.
Gibberella Stalk Rot
Again, the symptoms are very similar to Fusarium and Diplodia with
the pith of the inner stalk deteriorating and leaving only the vascular
bundles intact. The vascular bundles will appear reddish in color.
Small black specks may also be present on the stalk. With Gibberella, you can scrape these small black specks off with your finger
nail, while the small black specks of Diplodia are embedded in the
stalk and you cannot scrape them off. To the right is the internal
symptom of Gibberella.
SOYBEAN STAGE OF DEVELOPMENT:
Identifying soybean Stage of Development is essential for understanding how soybean pests or other problems affect yield. The following method was developed by Iowa State University and is followed by most industry, extension and research scientists. When attempting to determine a stage; be sure to observe plants
throughout the field because variation occurs within any field. A stage occurs for a field or sample when 50%
of the plants are at the stage in question.
Subdivisions of the reproductive stages are designated numerically
R1 through R8 and described below
Stage
R1
R2
R3
R4
R5
R6
R7
R8
Description
One flower open at any node on main stem
Open flower at one of the two uppermost nodes on main stem with a fully developed leaf
Pod 3/16 inch long at one of the four uppermost nodes on main stem with a fully developed leaf
Pod 3/4 inch long at one of the four uppermost nodes on main stem with a fully developed leaf
Seed 1/8 inch long in a pod at one of the four uppermost nodes on main stem with a fully developed
leaf
Pod containing a green seed that fills pod cavity at one of the four uppermost nodes on main stem
with a fully developed leaf
One normal pod on the main stem that has reached its mature color
95% of the pods have reached their mature color
SOYBEAN POD FILL:
Soybeans are moving through their reproductive stage of development and will soon be approaching R5, or beginning seed. At R5,
soybeans may have flowers, pods and pods with seeds just developing in them. This is a critical stage for yield development because after this stage, flowering will end and the chance of the
soybean plant to add more yield will be dramatically reduced because new pods cannot be added to the plant. At the R6 stage
the soybean has accumulated about 95% of its seed yield and
from this point typically the soybean is 15-20 days from physiological maturity. The time from physiological maturity to harvest depends much on the kind of weather conditions we have. Hot, dry
weather or a killing frost will quickly move the crop to a harvestable
condition.
CONTINUE TO MONITOR SOYBEANS FOR INSECT
DAMAGE:
Soybean aphid populations have been on the rise in portions of
the Area and some fields have reached treatment thresholds.
Research has shown that we need to continue scouting for aphids
until the R6 stage of development. Fields that were treated earlier
in the growing season with an insecticide, still need to be monitored for soybean aphids, as populations may increase in those
fields because the beneficial insects have been killed by the insecticide used for treatment, or the residual may have worn off.
Other insects, such as bean leaf beetles, grasshoppers and
woolly bear caterpillars can also cause damage to soybean
leaves. Soybeans can tolerate up to 25% defoliation before control measures are needed with such insects. However, as soybean leaves age and begin to lose their green color, insects may
begin feeding on pods. Pod feeding is a more serious issue than
leaf feeding. By feeding on pods, bean leaf beetles and other
insects expose seeds to pathogens which may result in
shrunken, discolored seeds. Typically, feeding damage on 510% of the pods is enough to warrant treatment.
PONCHO1250 + VOTIVO™:
Poncho1250 + Votivo™ is a seed treatment being offered from Pio-
neer that provides a biological mode of action that helps protect
corn roots against nematodes. Poncho 1250 + Votivo includes a
bacteria that is applied to the seed and once the seed is planted,
the bacteria will grow and multiply and colonize on the roots.
Poncho 1250 +Votivo does not directly kill nematodes. The bacteria compete with nematodes for space and food resources,
thus providing a barrier between the nematodes and corn roots.
The bacteria consume root exudates, which nematodes use as a
food source and as a way to find plants. As a result of the consumption of the root exudates by the bacteria, nematodes have
more difficulty finding roots and with a reduction in food source,
some of the nematodes may die.
Poncho1250+Votivo is available on several Pioneer corn hybrids
for the 2012 planting season. See your local Pioneer sales rep
for more information on availability.
WALKING YOUR FIELDS ®
PIONEER HI-BRED INTERNATIONAL, INC.
7100 NW 62nd Ave., P.O. Box 466
Johnston, IA 50131
Walking Your Fields ®
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Product & Technology Corner
Pioneer 2012 Featured Hybrids
Hybrid
CRM
Trait
Highlights
P9910AM1
99
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Excellent roots, drought tolerance, & late season standability.
P0115AM1
101
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Above average stress emergence, stalk strength, & drought tolerance.
P0448AM1
104
Triple
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P0453HR
104
Double
P0463AM1
104
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34F07
109
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P1162AM1
111
Triple
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P1395AM1
113
Triple
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Strong disease tolerance, drought tolerance, & stalk strength.
Tremendous yield potential with a solid disease package.
Solid performance for many years across many environments.
All products are trademarks of their manufacturers
AM1 – Contains the Optimum® AcreMax™ Insect Protection System with an integrated refuge solution.
HX1 - Pioneer® brand corn hybrids with Herculex® I Insect Protection trait. HXX - Herculex® XTRA contains the Herculex® I and Herculex® RW genes. Herculex® I Insect,
Herculex® RW Rootworm, Herculex® XTRA Insect Protection technology by Dow AgroSciences and Pioneer Hi-Bred. LL - Pioneer® brand corn hybrids with the LibertyLink ®
gene. LibertyLink is a trademark of Bayer. Pioneer® brand soybeans with the Roundup Ready® gene. RR2 - Pioneer® brand corn hybrids with the Roundup Ready® Corn 2
gene. Roundup Ready is a registered trademark used under license from Monsanto Company.