Fall Scouting and Evaluating Field Test Plots and Demonstration Strips
Originally written September 18, 2004 | Last updated
February 23, 2014
crop managers try new things every year and constantly evaluate their
management practices. Some new practices work and fit into their management
style, others don't. Lessons learned producing this year's crop will help
with next year's crop.
Growers should continue scouting right through harvest.
Growers need to monitor fields carefully, and plan harvest schedules to
begin with fields where stalk and root deterioration appears worst. Below
are some things to check in your fields yet this year for timing harvest,
and to consider in your plans for next season. Record information. Keep a
notebook or computer file. It is difficult to commit things to memory,
especially two or three seasons into the future.
Fall Field Scouting
Check for ear-tip fill. Incomplete ear-tip fill is not necessarily bad. If
kernels are filled out completely to the ear tip, plant populations are
likely too low for conditions. Expect about an inch of underdeveloped
kernels at the ear tip if plant populations are at a high enough level to
optimize grain yield per acre.
Check kernel development on the ear. Look for differences in how well
different hybrids have held up to management practices (i.e. herbicide
application, irrigation stress, N stress, etc.) and weather stresses. Early
stress from weed competition or low N will reduce kernel row number and
kernel number per row. Severe heat and moisture stress during the first
seven to ten days after pollination will cause kernels at the tip of the ear
to abort. Stress around pollination reduces cell division and potential
starch fill causing shallow kernel depth and lighter test weight.
Check the maturity of hybrids in your fields and relate back to planting and
emergence dates. Following the rate of drydown using kernel milkline is a
good way to predict the order fields should be harvested. In a typical year
a common benchmark is that fields should be dented by the first week in
September. It takes about 30 days to go from dent to black layer
(physiological maturity); about 15 days to get to 50% kernel milk and
another 15 days to black layer. Kernel moisture at black layer will average
32 to 35 percent. The tightness of the husk, thickness of the seed coat and
daily weather conditions influence the speed of kernel drydown. After black
layer formation several hard frosts followed by sunny weather with
temperatures in the 80's and a slight breeze is the ideal drying
Hybrids differ in the time it takes to reach harvest moisture from black
layer. A rough estimate is that 15 to 20 GDUs/point of moisture are needed
to lower the moisture from 35 to 25 percent. It takes 20 to 25 GDUs/point of
moisture to dry the grain from 25 to 20 percent.
Scout for corn standability. Fields that have lodging problems can be
identified and targeted for the earliest possible harvest. Look for visible
symptoms and test stalk firmness by pinching the lower internodes with your
thumb and forefinger. Healthy stalks are firm and can't be compressed. If a
stalk can be compressed or feels soft, it is rotted and is a good candidate
Check for rapid "die-down." The lower portion of corn plants in some fields
deteriorates rapidly. Lower leaves first appear nitrogen-stressed, then turn
brown and die. Other factors such as compaction, dry weather, herbicide
injury or root pruning by insects can also cause these symptoms. Some of
these plants may be experiencing low nitrogen availability due to losses
from leaching and/or denitrification following excessive rain.
In most cases it is more likely due to remobilization of nutrients from the
stalk to the grain, a sort of "cannibalism." Cool, cloudy days and warm
nights produce low levels of photosynthesis (sugar production) during the
day with high rates of respiration (sugar breakdown) at night. When the
plant's nutrient availablity is limited due to low photosynthesis, sugars
already produced and stored in the stalk are often "moved-out"
(translocated) to help fill the ear. Another factor that might be
responsible for rapid die-down is the development of pathogens that cause
root and stalk rot. Wet soils and cloudy humid conditions favor these
diseases. Corn stalks weakened by remobilization of nutrients to the ear are
especially vulnerable to root and and stalk rotting organisms.
During combining inventory weed problems. Use a map and list details such as
location of broadleaf and grass species, population density of the crop and
weed, and response to herbicides. Watch for new weeds. Watch for any weeds
that may be developing resistance to herbicides.
In preparation for next year, assess soil fertility levels by pulling soil
Resist estimating yield differences between corn hybrids - measure it. Field
variability alone can easily cause apparent differences of 10 to 50 bushels
per acre. Make notes bout "ease of combining." Test weight and grain
moisture can influence hybrid yield. There are "quickie" measures of
potential grain yield, but you shouldn't expect much precision with these
In general, there are two major categories of on-farm research
trials. The first is replicated trials that try to account for
field variability with repeated randomized comparisons. Examples include trials
conducted by universities and by public and private plant breeders. The
other type is non-replicated demonstrations such as yield contests, on-farm
yield claims, demonstration/strip trials and farmer observation and experience.
Evaluating Research Test Plots
Field variability alone
can easily account for differences of 10 to 50 bushels per acre. Be
extremely wary of strip plots that are not replicated, or only have "check"
or "tester" hybrids inserted between every 5 to 10 hybrids. The best test
plots are replicated (with all hybrids replicated at least three times).
Don't put much stock in results from ONE LOCATION AND ONE YEAR, even if the trial is well run and
reliable. This is especially important in years with tremendous
variability in growing conditions. Years differ and the results from other
locations may more closely match your conditions next year. Use
data and observations from university trials, local demonstration plots, and
then your own on-farm trials to look for consistent trends.
A few suggestions on how to evaluate research test plots:
- Walk into plots and check plant populations. Hybrids with large ears or two
ears per plant may have thin stands.
- Scout for pest problems. Hybrid differences for pest resistance and
tolerance should be monitored and noted all season, but will be most
apparent in the fall.
Counting dropped ears is a good way to measure hybrid ear retention and
tolerance to European corn borers.
- Check for goose-necked stalks. This is often root pruning caused by corn
rootworms. Hybrids differ in their ability to regrow pruned roots.
- Find out if the seed
treatments (seed applied fungicides and insecticides) applied varied among
hybrids planted, e.g. were the hybrids treated with the same seed applied
insecticide at the same rate? Differences in treatments may affect final
stand and injury caused by insects and diseases.
- Differences in standability will not show up until later in the season
and/or until after a wind storm. Pinch or split the lower stalk to see
whether the stalk pith is beginning to rot.
- Break ears in two to check relative kernel development of different hybrids.
Hybrids that look most healthy and green may be more immature than others.
Don't confuse good late season plant health ("stay green") with late
- Visual observation of ear-tip fill, ear length, number of kernel
rows, and kernel depth, etc. don't tell you much about actual yield
potential. Hybrid differences
are common for tip kernel abortion ("tip dieback" or "tip-back") and "zipper ears" (missing kernel rows). Even if
corn ear tips are not filled completely, due to poor pollination or kernel
abortion, yield potential may not be affected significantly, if at all,
because the numbers of kernels per row may still be above normal.
- Be careful with test plots consisting predominately of one company's
hybrids. Odds are stacked in their favor!
Evaluating Demontstation or Strip-Trial Plots
Every fall many farmers visit and evaluate hybrid demonstration plots
planted by seed companies and county Extension personnel, among others. When
checking out these plots, it's important to keep in mind their relative
value and limitations. Demonstration plots may be useful in providing
information on certain hybrid traits, especially those that are usually not
reported in state corn performance summaries.
Use field days to make careful observations and ask questions, but reserve
any decisions until you have seen the "numbers." Appearances can be
PLANT/EAR HEIGHT. Corn
reaches it maximum plant height soon after tasseling occurs. Remember that
although a big tall hybrid may have a lot of "eye appeal," it may also be
more prone to stalk lodging in the fall. Unless your interest is primarily
silage production, increasing plant height should not be a major concern.
Generally later maturity hybrids are taller than earlier maturity hybrids.
Big ears placed head high on a plant translate to a high center of gravity,
predisposing a plant to potential lodging. The negative effects of stalk rot
on stalk lodging in the fall may be worsened by high ear placement. Plots
that have been subjected to early season (V7 or earlier) defoliation caused
by hail or frost often have lower than normal ear height.
STALK SIZE. Generally
speaking, a thicker stalk is preferable to a thinner one in terms of overall
stalk strength and resistance to stalk lodging. As you inspect a test plot,
you will see distinct differences among hybrids for stalk diameter. However,
also check that the hybrids are planted at similar populations. As
population increases stalk diameter generally decreases. Keep in mind
that uneven emergence and development may make such comparisons difficult because late emerging plants are
DISEASES. During the grain
fill period, leaf diseases can cause serious yield reductions and predispose
corn to stalk rot and lodging problems at maturity. Ear rots can also impact
yield and grain quality. The onset of leaf death shortly after pollination
can be devastating to potential yield, since maximum photosynthetic leaf
surface is needed to optimize grain yield. Hybrids can vary considerably in
their ability to resist infection by these diseases. Demonstration plots
provide an excellent opportunity to compare differences among hybrids to
disease problems that have only occurred on a localized basis. Look for
differences in resistance to northern corn leaf blight, gray leaf spot, and diplodia
Check to see if foliar
fungicides have been applied and what crop rotation has been followed.
Typically you'll encounter more severe foliar disease problems in no-till,
STALK ROTS. Hybrids will
likely differ widely when faced with strong stalk rot pressure. Begin
checking plants in late August or about 6 weeks after pollination by
pinching lower stalk internodes with your thumb and forefinger. Stalks that
collapse easily are a sure indicator of stalk rot. Remember that hybrids
with thicker stalks may be in plots having thin stands.
LODGING. Perhaps as important
as stalk rot resistance is the stalk strength characteristics of a hybrid.
Sometimes, superior stalk strength will limit the adverse effects of stalk
rot. If your variety plot is affected by stalk rot in late August and early
September, evaluate stalk lodging of the different hybrids. Most agronomists
characterize plants with stalks broken below the ear as stalk
lodged plants. In contrast, corn stalks leaning 45 degrees or more
from the center are generally described as root lodged plants; broken
stalks are usually not involved. Root lodging can occur as early as the
mid-to- late vegetative stages (as it did this year) and as late as harvest
maturity. Both stalk and root lodging can be affected by hybrid
susceptibility, environmental stress (drought), insect and disease injury.
Root lodging may be
associated with western corn rootworm injury. However, much root lodging occurs as the result of other factors, i.e. when a hybrid susceptible
to root lodging is hit by a severe windstorm. A hybrid may be particularly
sensitive to root lodging yet very resistant to stalk lodging. A cornfield
may exhibit extensive root lodging in July but show little or no evidence of
root lodging at harvest maturity in September (except for a slight "goose
necking" at the base of the plant).
TRANSGENIC TRAITS: Because
damage from European corn borer (ECB) and western corn rootworm (RW) can be
very localized, strip plot demonstrations may be one of the best ways to
assess the advantages of ECB Bt and RW Bt corns. The potential benefit of
the ECB Bt trait is likely to be most evident in plots planted very early or
very late; the potential benefit of the RW Bt trait is likely to be most
evident in plots planted following corn or in a field where the first year
western corn rootworm variant is present.
HUSK COVERAGE/EAR ANGLE.
Hybrids will vary for completeness of husk coverage on the ear as well as
tightness of the husk leaves around the ear. Ears protrude from the husk
leaves are susceptible to insect and bird feeding. Husks that remain tight
around the ear delay field drydown of the grain. Hybrids with upright ears
are often associated with short shanks that may be more prone to ear and
kernel rots than those ears that point down after maturity. Differences in ear
"orientation" among hybrids can be strongly
influenced by growing season and plant density. Also, under certain
environmental conditions, some hybrids are more prone to drop ears, a major
problem if harvesting is delayed.
Remeber that yield
is not a beauty contest. Some "ugly" hybrids are good performers. Don't over
emphasize results from one type of trial. Use data and observations from
university trials, local demonstration plots, and then your own on-farm
trials to look for consistent trends.
Buy hybrids ... don't be sold based on fancy result books and plot signs,
flags, streamers, caps, brats, etc.
Remember safety as you move into the
harvest season this year.