Dr. Dan Talks Agronomy 06/30 15:29
Early Season Corn Scouting Offers Many Benefits
Scout everything from seed placement, plant stand, growing conditions, weeds
and fertility concerns.
By Daniel Davidson
DTN Contributing Agronomist
OMAHA (DTN) -- With our nation's holiday only a week away, it's hard to
imagine that most of the corn will only be knee-high by the Fourth of July. And
it varies greatly, from seed that has been in the ground for only a few weeks
(such as in Ohio), compared to seed that hit the ground two months ago for much
of the Western Corn Belt.
With the end of June almost here, post herbicides are being applied and
growers should be finishing up sidedressing nitrogen by next week.
Despite this late spring, make sure you take time to scout corn. It is a
vitally important activity in order to judge how planting went, what weed
pressure is occurring and if the crop is off to a good start or not. When I'm
out walking my fields, here are some key things I like to do.
First: Record the crop leaf stage and note how it is similar or different
from last year. Recording the growth stage is easy during June because you can
still see the remnants of the first plumule leaf and first true leaf. From
there, you simply count the number of collared leaves up from the bottom of the
Come July, the first two leaves have usually fallen off. So to get a true
leaf stage you have to split the base of the plant and count leaf nodes (see
helpful link at bottom of story). The V growth stage is important because when
you get out to V8, it is too late to apply most postemergence herbicides, other
than perhaps glyphosate.
Second: Look at plant stands. This is a crucial observation in early corn
scouting. Is emergence consistent and is the population near your target? If
gaps exist, first look for seed. Was there an operator error, or mechanical
error that caused seed not to be planted? Check your planter condition now
while it's fresh on your mind, and make plans for repairs before next spring.
If seed drop was consistent, then it was probably something else. Did the
seed germinate? Cold, wet conditions are the primary causes of seed death
during imbibition. Did the seed rot? Seed fungicides protect the seed and
seedlings for about 30-40 days after planting, but can be overwhelmed by the
pathogen if prolonged soil conditions are cool and wet.
Are insects feeding? Seed corn maggot and wireworm are insects usually
associated with corn emergence failures. Or are wireworms or cutworms clipping
off the seedling?
Third: Check planting depth. You should do this at planting and after crop
establishment. Dig up a few seedlings. The growing point will be three-quarters
of an inch below the soil surface. To calculate planting depth, measure the
length of the mesocotyl (the stem structure between the seed and the growing
point). Its length flexes, so the growing point is set at three-quarters of an
inch deep. Then add the two values together (three-quarters of an inch plus
length of the mesocotyl) and you have planting depth.
Did you hit your target depth? Shallower-planted corn (less than 1 inch) may
emerge later due to drier soil surfaces and greater temperature fluctuations.
Plant too deep and emergence will be inconsistent. Make sure root tips are
pointed down and shoots up and not wrapped up or unfurled. If roots seem
trapped and growing laterally in the furrow, it's likely you have sidewall
compaction of the furrow.
Fourth: Note weed species and height. While weed pressure is important and
it will be variable across a field, most growers are going to spray to take out
those weeds and keep the weed seed bank count low.
If you want to prevent competition and maximize weed control, knock weeds
down when they average around four inches in height. I know there is a tendency
to delay spring glyphosate application until the weeds are taller and more of
them are present. However, this is a risk to both control and competition to
Fifth: Look for early season nutrient deficiencies like nitrogen (yellow),
phosphorus (reddish), or zinc, manganese or iron (yellow striations on leaves).
The crop is still small enough that you can remediate the problem with either a
soil or foliar application.
Corn growth stages
Early season cold stress
Daniel Davidson can be reached at firstname.lastname@example.org
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