Late Corn Planting Dates and Potential Yields
Chad
Lee
May 21, 2008
All
of you know that corn planting is late across the state this year. According to
the Kentucky Field Office of the USDA National Agricultural Statistics Service,
about 73% of the corn was planted by May 18, compared to 90% planted for the
five-year average and 95% planted by this time last year.
The
late planting of corn typically results in yield losses. However, 2008 has not
started out as a typical year. Our challenge is to look at the historical
planting data and compare those results with the conditions we see in 2008.
The
state historical data implies lower state average corn yields when less corn is
planted by the third week of May (Fig. 1). Corn planting in Kentucky has been
at or less than 80% planted by the third week of May in seven years of the past
18 years. State average yields have done well in two of those years. Based on
the planting progress of the past 18 years, the odds are not in favor of a high
average state corn yield for 2008.
Figure 1. Kentucky planting progress and average state yield. Data
from the USDA-NASS.
The
most recent planting date studies conducted by Drs. Jim Herbek and Rick Bessin
showed about a 1% per day yield loss for corn planted after May 5 at Princeton,
Kentucky. Older research suggests that the yield losses do not kick in until May
10-15. Based on this research, corn planted May 30 would have lost about 20 to
30% yield potential. Your 200 bu/acre corn field would be expected to yield
about 140 to 160 bu/acre. Most of the research was conducted in years where we
were able to plant corn early and late. This year did not allow us to plant
corn early.
Corn
Growing Degree Days from April 1 to May 20, 2008 are much less than normal for
many areas of Kentucky (U.K. Ag Weather Center). For example, Mayfield,
Paducah, Princeton and Henderson all should have 672 heat units accumulated
between April 1 and May 20. However, Mayfield had 521, Paducah had 562,
Princeton had 602 and Henderson had 511 heat units. Corn that was planted is
off to a slower start this year. Or another way of looking at this is that any
late planted corn is not as late as usual for this time of year.
So,
how will late planting corn affect yield? The research suggests we start losing
yield potential for corn planted sometime after May 5 to May 15. However, with the cool start to this year, the yield loss potential for late-planted corn compared with early-planted corn is probably less this year.
Key Tips You Will
Probably Ignore for Late Planted Corn
1. Wait one more
day. Mudding in
corn may work if we get timely rains every week throughout the summer. However,
mudding in often leads to sidewall compaction and restricted root growth which
leads to other problems in the growing season. If you are able to choose
between mudding in the corn or waiting the extra day for soils to dry, you will
be better off to wait that extra day. The challenge with waiting one more day
is 1) you have a lot of acres to get planted and 2) no one can guarantee if
that one more day will be dry. So, if you mud in corn, then be prepared to
scout those fields for problems later. Maybe we will get timely rains every
week and this won’t become a problem.
2. Slow down. Most planters work best at about
4 to 6 mph. Slower speeds allow for more uniform placement of seed. I know, you
are already late getting corn planted and I’m asking you to drive slowly.
3. Check planter
depth in every field.
Soil moisture will affect planting depth, with the planter sinking deeper in wetter
soils and shallower in drier soils. You are targeting a depth of about 1.5
inches. The depth settings on your planter will be correct for one field and
off on the next depending on soil type, soil moisture and residue. Getting the
correct seed depth will lead to better results later in the season. Take the
time to check planter depth in each field.
4. Keep seeding
rates the same.
With the potential for reduced yields, some farmers may be tempted to lower the
seeding rate. Keep the seeding rates the same as you normally would for a
field. The recommended range is about 24,000 to 30,000 viable seeds per acre,
with the higher end of the range for more productive soils. If your normal
practice is to plant more than 30,000 seeds per acre, you may not need to be as
high.
5. Keep hybrid maturities the same for May, switch for June. If you can get the corn planted in May, you are probably safe to stay with the seed you already have. Once we get into June, you may want to switch to an earlier-maturing hybrid. If possible, you may want to switch to a cornborer Bt hybrid, for any additional corn to be planted. Research has shown a yield advantage to cornborer Bt corn planted early May or later.
6. Control weeds. Late-planted corn normally
germinates and emerges much quicker than early-planted corn. Weeds will also
grow a little faster this time of the year. You likely have some yield
reductions from the late plantings. Do not add to the problem by letting weeds
get too big. Depending on the year, weeds that emerge with the crop and reach
six inches in height will reduce yields. Because the corn should grow a little
quicker, be ready to spray your postemergence treatments earlier than you normally
do. Count collars on the corn (fully emerged leaves) before spraying to make
sure your corn is not too mature for the herbicide application.
So,
planting corn late usually results in reduced yields. However, this is not your
usual year. Perhaps our heat units will catch up and we will have the water we
need for a little faster corn growth. While we are not off to the best start,
maybe, just maybe we can have a good finish.