WEST LAFAYETTE, Ind. — Much of Indiana’s once-thriving corn
crop continues to deteriorate as hot, dry conditions continue their stranglehold
on much of the state, a Purdue Extension corn specialist said.
The combination of dryness and extreme heat during critical
weeks for corn kernel weight development is further cutting into yield
“Plain and simple, the ‘frosting is off the cake’ for many
cornfields around Indiana as dry and often excessively hot conditions continue
through the end of this 2013 grain-filling period,” Bob Nielsen said. “In fact,
for some fields, the ‘cake’ is disappearing, too.”
The U.S. Department of Agriculture’s Drought Monitor update
of Sept. 5 showed that about one-third of Indiana was abnormally dry — the
lowest level of dryness — while a small swath of the northwestern part of the
state fell into moderate drought.
On Sept. 9, the U.S. Department of Agriculture reported that
an estimated 67 percent of Indiana’s corn crop is at the dent stage of kernel
development. That leaves nearly one-third of the crop in dough stage, meaning 50
percent of its yield potential is yet to be determined.
According to Nielsen, there is a common misconception that
growers don’t have to worry about yield potential when corn has hit dent.
“Once corn reaches dent stage, many folks can be heard
confidently stating that there is no reason to worry about further crop stresses
because ‘the crop is made,’” he said. “Actually, by the time a crop reaches full
dent, only about 60 percent of the crop has been ‘made’ and there is still 40
percent of the potential yield on the table yet to be determined.”
In fact, corn plants still can fall victim to sudden and
complete death as late as two weeks before physiological maturity if conditions
are bad enough, Nielsen said. Whole plant death can translate to yield losses as
high as 12 percent.
“A crop is not ‘made’ until it has successfully reached
physiological maturity,” the agronomist said.
Growers recognize physiological maturity when they can see a
thin, black layer at the tips of kernels, which prevents further photosynthate
into the grain.
Some of Indiana’s most stressed corn plants can be found in
soils that have low water-holding capacity or significant soil compaction.
Plants in those fields have shown stress in the form of leaf rolling, lower leaf
death or whole plant death.
But even crops planted in high-quality soils are showing
signs of stress.
“The effects of inadequate rainfall throughout much of the
grain-filling period in Indiana and elsewhere have, at times, been amplified by
the effects of excessively warm temperatures,” Nielsen said.
“Certainly not every field of corn is in dire straits at the
moment. Certainly there will be fields of corn that yield well or possibly
better than they ever have in the past. Just as certainly, there will be fields
with significant yield losses due to excessively dry soils and excessively hot
temperatures during the past 30 days or so.”
Severe stress this late in the growing season, especially
during grainfill after successful pollination and kernel set, can cause plants
to ‘cannibalize’ themselves to meet carbohydrate needs of developing grain,
Corn plants taking stored carbohydrate reserves in lower
stalk and leaf tissues and moving them to developing ears can cause weakening of
lower stalks and higher risk of root and stalk rots.
“Such cannibalized or diseased plants are naturally more apt
to break over or lodge in response to strong winds, potentially turning grain
harvest into a frustrating and challenging operation,” Nielsen said.
“Growers ought to be walking drought-stressed fields during
the next several weeks to assess the presence and severity of weakened stalks,
then work toward prioritizing the weakest fields for early harvest to minimize
the risk of significant mechanical harvest yield losses.”