Download Timely Grain Harvest

Agronomic Sheet
Timely Grain Harvest
What you need to know
It’s more important to save yields than to save on drying costs.
It’s time to start thinking about harvesting your corn. With the cool,
wet start to the summer followed by a dry period in August, we
need to be on the watch for lodging and stalk rots.
PHYSIOLOGY OF STALK CANNIBALIZATION
Corn plants must produce enough carbohydrates (sugars) by
photosynthesis to meet the demands of grain fill plus keep the
cells in both the stalk and roots alive. When the corn plant is
subjected to drought stress during grain fill, the photosynthetic
activity is reduced and the result is that there are insufficient
carbohydrates for the developing ear. The corn plant responds to
this situation by removing carbohydrates from the leaves, stalk
and roots and uses them to fill the grain. This is referred to as
cannibalization of the corn stalk. This process ensures a supply
of carbohydrates for the developing ear, however, the removal
of carbohydrates from the stalk results in a rapid deterioration
of the lower portion of the plant with lower leaves appearing to
be nitrogen stressed, brown and/or dead. This weakening of the
stalk makes the plants vulnerable to lodging and also predisposes
the plants to root and stalk infection by fungi such as Gibberella,
Collectotrichum (anthracnose) and Fusarium.
Other plant stresses which increase the likelihood of stalk
problems include:
•Loss of leaf tissue due to foliar diseases (such as grey leaf spot
or northern corn leaf blight), insects or hail
•Injury to the root system by insects or chemicals
•High levels of nitrogen in relation to potassium
•Compacted or saturated soils restricting root growth
•High plant populations
With cannibalization and stock lodging an issue this year,
growers need to be monitoring grain moisture. It’s important
to start monitoring grain moisture as soon as physiological
maturity (black layer) is reached. Corn moisture at black layer
should be around 30%. Allowing corn to dry too long in the
field increases the risk of lodging, yield losses and stalk rots.
When cannibalization is a problem during the growing season,
the risks increase.
Temperature, humidity, weather and grain maturity influence grain
drying rates. Warm, dry weather speeds up the crop drying rate;
cool, wet weather slows down the drying rate. Successful grain
harvests can be accomplished when grain moisture is 28% or
lower, and it is more important to maintain yields by harvesting
at higher moisture than to try to minimize drying costs by leaving
your fields at risk to yield robbing lodging or stalk rots1.
When 10-15% of plants are found to lodge or are rotted,
consider early harvest for that field.
Fields that experience 2 or more of the causes of stalk
cannibalization are good candidates for monitoring and
early harvest.
ECONOMIC EFFECT OF LODGING
Lodging not only makes harvesting difficult, but it has an
effect on your pocketbook as well. OMAFRA research found
that 5% lodging loss could cost $35-40 per acre (based on
160‑200 bu/ac yield, $4.50/bu corn)2. This loss would pay
to dry 4-5 points of moisture per acre of corn production.
SCOUTING FOR LODGING AND STALK ROT
There are two methods for scouting for lodging and stalk rots that
can help determine if early harvest is necessary. For either method,
select 20 plants from five different locations in the field for a total
of 100 randomly selected plants.
1.Push Test – the top portion of each plant is pushed
15-20 cm (6-8 in) from the vertical. Number of lodged
or broken plants is recorded.
2.Pinch or Squeeze test – the area above the brace roots
is squeezed. This is particularly useful for identifying plants
with stalk rot. The number of stalks that can be compressed
is recorded.
Push Test
Lodged Corn
1
lmore, R and L Abendroth. 2010. Impact of in-field drydown rates on corn
E
harvest. Iowa State U. www.extension.iastate.edu
2
OMAFRA 2015 Field Crop Budgets
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