Stalk Quality, Yield, and Corn Hybrids:
Was the "Nightmare of 2000" a Fluke?
Many Illinois corn producers will remember the 2000 crop year as a most unusual
growing season. Following very dry weather from late summer 1999 through the
planting season and some alarming predictions of drought that were made in March,
there was widespread concern that drought would cause major crop losses. No
one would have predicted at that time how the season would go. A brief recap:
| 1. |
Planting began very early - there were reports of planting
in early March - and proceeded quickly, with 58 percent of the crop planted
by April 30 and 98 percent planted by May 14. |
| 2. |
Drought fears eased with near-normal rainfall over most of
the state in May and above- to much-above-average rainfall during June. |
| 3. |
May temperatures were slightly above average in southern Illinois
and much above average in northern Illinois, but were below average over
much of the state in June; GDD accumulations from May 1 to June 30 were
about average. |
| 4. |
The addition of as many as 200 GDD from early planting resulted
in early pollination, with almost 75 percent of the crop silked by mid-July,
compared to a five-year average of only about 25 percent. |
| 5. |
Conditions during pollination could hardly have been better:
the first two weeks of July featured normal temperatures and rainfall totals
between 2 and 4 inches in most areas. |
| 6. |
From mid-July through the first three weeks of August, temperatures
remained normal to below normal, but rainfall was low, especially in the
central part of the state. Southern Illinois stayed wet. |
| 7. |
At the end of August into early September, there occurred
more than a week of very high temperatures - as much as 13 degrees above
normal - with no appreciable rainfall. |
| 8. |
Harvest of the corn crop, especially in areas that had been
dry since July, began in late August. Grain moisture at harvest was low
in these areas. |
The corn crop in Illinois responded to this growing season weather in
the following ways:
|
| 1. |
The crop responded to the near-ideal planting conditions with
very good stands. |
| 2. |
Early planting and good stands along with weather in May and
June resulted in a crop that, by early July, looked outstanding: 86 percent
of the crop in the state was rated as "good" or "excellent"
on June 30. Exceptions were in the very wet areas of southern Illinois.
Leaf rust was also more widespread than usual with the cool, wet June weather. |
| 3. |
Moderate temperatures and very good water supplies during
the first half of July resulted in what was likely the best pollination
success ever in the Illinois crop. High plant populations and high kernel
counts per ear combined to make very high kernel counts per acre. |
| 4. |
As rainfall tapered off in July and nearly stopped in parts
of central and northern Illinois in August, grainfilling was extremely rapid,
but stress was starting to limit photosynthetic rates in many fields, even
though water stress symptoms were not very visible. |
| 5. |
The high kernel counts and the good weather at pollination
resulted in what I'll call "hungry" kernels - the draw by the
kernels on the resources of the plant (mostly on the sugars produced by
photosynthesis and moved into the stalk) was probably as high as it's ever
been. |
| 6. |
This strong "draw" by the ear pulled most available
resources from the stalk, and likely resulted in inadequate nutrients to
produce normal stalk growth. Disease organisms always can move into the
stalk when this happens, but in many fields the stalks themselves probably
did not have enough sugars to form normal amounts of lignins and other materials
that normally stiffen the stalk. |
| 7. |
We can't assess root systems very well during the season,
but wet weather in June might have reduced root size somewhat. Dry weather
effects in August probably harmed root function considerably, and loss of
nutrients from the stalk likely starved the roots. As a result, roots were
probably not able to resist disease attack very well, nor were they able
to help maintain supplies of nutrients and water to the plant when it needed
them. |
| 8. |
Fortunately, the early planting and average temperatures,
coupled with early pollination that tended to move grainfill into the warmer
part of the summer, had the crop moving toward maturity very early, especially
in central Illinois. When the very high temperatures in late August hit,
therefore, the crop was close to maturity, so the high temperatures and
lack of water were less damaging. (Soybeans suffered much more than corn
from this, because they were not as far along in development.) Still, the
week-long high temperatures ended grainfilling in fields with dry soils,
and probably contributed to weak stalks. |
| 9. |
Even with these problems, the statewide yield average projected
in early August was 159 bushels per acre, which would have made it the highest
yield on record. That dropped in later months, but the current estimate
is 153 bushels per acre, which is only 3 bushels less than in the record
year of 1994. |
The description above seems to describe a crop season that was very favorable
for corn, with little to complain about in terms of yield. The bad news in 2000,
at least for a sizable number of producers, was the poor stalk quality: an estimated
20 to 25 percent of the corn crop in Illinois suffered moderate to severe stalk
quality problems. Reasons for this
are outlined above, but the very slow harvest progress and stress of running
combines so slowly and carefully left many producers saying "Never again,"
especially with those hybrids that didn't stand next to those that did. What
conclusion can we draw about hybrid performance and stalk quality, and what
should we do in the future to prevent this problem?
On the good news side, the modern combines that most producers are using are
much better at picking up lodged corn than were combines in earlier generations.
Yield losses were not estimated on a systematic basis, but were reported by
producers to be as high as 15 or 20 bushels per acre. In the 1960s, that figure
would likely have been at least double that, if not higher. There are also attachments
that have been developed to help move corn into the gathering chains, and larger
engines have increased the threshing and separation capacity so that large quantities
of stalk that broke apart and went through the machine could be more easily
handled.
Even though the pain of harvest will fade some with time, producers have more
than usual interest in choosing hybrids that will not lodge as badly as some
did in 2000. Hybrid differences in susceptibility to lodging were large and
very noticeable this year. While such genetic differences have always existed
among hybrids, overall selection for standability by breeders has resulted in
these differences not being very visible in most years. In the 1999 University
of Illinois hybrid trials, average stalk breakage for all hybrids on a regional
basis ranged from zero to only 2 percent.
The hybrid testing data from the U of I trials in 2000 illustrate the severity
of the stalk breakage problem. At the Monmouth location, breakage was so severe
that we could not harvest the trial for yield, and average breakage among the
other 11 locations ranged from 65 to 98 percent. With one exception (Goodfield,
in Woodford County), where the standability and yield were both low, there was
a slight trend toward lower yield with higher standability. This might be expected, based on the fact that large ears and strong
draw on the stalk nutrients might have resulted in both higher yields and lower
standability, except in the driest location, where stalks were likely depleted
so early that both the stalk and the kernels were starved for nutrients. This
conclusion is supported by the fact that Goodfield was the driest location among
all of the trials, with only 1.5 and 1.6 inches of rainfall in July and August,
respectively. In contrast, the highest-yielding location - Perry (Pike County)
- received 3.6 and 3.5 inches in those two months.
Unfortunately, this relationship - a reward in extra yield for poor standability
- did not hold up particularly well for hybrids within a location. The Perry
location had the highest average yield and some stalk quality problems, but
the relationship between the two was not very strong. And in the Goodfield location, where lodging was severe, yields
were generally lower in those hybrids that lodged the most, but the overall
correlation between standability and yield was not very high. This is probably a matter of degree: where a standability problem
developed near maturity, it did not affect yield much, if any, while hybrids
that broke over early had poor stalk quality and also reduced yield.
In order to see if hybrids with the ability to produce high yields bring with
them the tendency to lodge, we matched the yields of hybrids from both 1999
and 2000 against lodging in 2000 at Erie (Whiteside County) and at Goodfield.
While the hybrids put back into these trials in 2000 tended to be the higher-yielding
ones from 1999 (which is no surprise), there was no relationship between lodging
in 2000 and yields in 1999 of the same hybrids.
From the results presented here, it is clear that that we don't automatically
choose lower stalk quality if we choose for high yields, nor do we compromise
yields if we choose hybrids based on standability. The unusual growing season
of 2000 was certainly one of the most effective tests for stalk strength that
many hybrids have ever experienced. While a repeat of such conditions in another
year may be unlikely, another season like 2000 would result in standability
problems in many of the same hybrids that had problems in 2000.
The important point is, however, that a repeat of the unique conditions of 2000
has to be considered unlikely. If we believe that, then it is much more important
to choose hybrids based on proven yield performance than on standability in
2000. Hybrids that are selected for "all-out yield" were, in many
cases, the ones that broke over the most in 2000, but they are also likely to
produce high yields under less stressful conditions. If we can estimate that
the chances of such conditions happening again are 10 percent (which is probably
high), then it might be reasonable to discount the expected yield advantage
of a higher-yielding hybrid over a lower-yielding one by that same 10 percent
- a 10-bushel expected advantage reduced to 9 bushels - but to decide never
again to use hybrids that did not stand well in 2000 could be a costly decision.
In the end, we should view hybrid choice as a type of risk strategy. Planting
high populations and using high rates of fertilizer and other inputs bring some
risk, but we do them for the reward of higher yield when conditions are good,
which in Illinois is most of the time. Hybrid choice involves some of the same
sort of risk, and we should accept it knowing that such risks don't always pay
off.
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