Corn Concerns & Curiosities

 A number of things are showing up in the corn patch, now that corn is actively growing and farmers/agronomists are scouting for emergence, growth and weeds.

  • Uneven emergence
  • Herbicide Injury
  • Scorthed Leaves
  • Wilted/Discoloured Corn
  • Sand-blasted Corn
  • Grey Corn Leaves
  • Yellow/Twited Corn Leaves

To see pictures and find out what is causing them see corn-concerns-curiosities (PDF 1.88MB)

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Hail Damage – What is the Yield Loss in Cereals & Corn?

Submitted by Anne Kirk, Cereal Crop Specialist, Manitoba Agriculture

Hail has been reported in several areas of Manitoba, and due to the size of the hail and duration of the storm, crops were affected in some areas.  Assessments of damage will occur over the next few days.  The amount of loss expected from a hail event depends on the severity of hail, crop type, and the growth stage of the crop.

Spring Wheat – is least susceptible to hail damage prior to stem elongation since the growing point is below the soil surface and will likely not be damaged.  Hail damage during jointing or in the boot stage is difficult to assess.  Spikes can still pollinate and fill, and regrowth from new tillers can occur.  The more advanced the wheat is at the time of hail the greater the yield loss.  The greatest yield reduction from hail occurs in the milk stage.

Oats and Barley –  will tiller and recover better from hail than wheat, especially prior to the boot stage.  Grower experience has demonstrated that barley hailed severely in the boot stage has recovered to produce 70-80% of normal yield.  Crop hailed prior to the boot stage should be left if stems or green tissue remains.

Corn – early season hail occurring when the growing point is still below the soil surface will result in very little yield loss.  At the 6 leaf stage the growing point is above ground, but leaf loss without damage to the growing point has a small impact on yield.  Yield loss as a result of hail can be estimated by determining percent leaf defoliation (Table 2).   Leaf area removed and leaf necrosis need to be considered, while damaged green leaf tissue should not be included.  Assess leaves 7-10 days after a hail event, so that living and dead tissue can be easily distinguished.

Assessing Damage – New growth should be evident within a few days after a hail event.  Assess crop to evaluate new crop growth.    Yield potential of a damaged crop will depend on rainfall and temperatures in the next 30 days after hail damage.

 

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Are You Staging Your Corn Correctly?

Submitted by Anne Kirk, Cereal Specialist, Manitoba Agriculture

For more information see Manitoba Corn Growers newsletter for Growth Stage Information for Herbicide Application

When applying post-emergent herbicides, proper corn growth staging is extremely important. Herbicide labels may refer to plant height, crop growth stage, or both when listing crop stage timing. Farmers and agronomists need to accurately stage corn plants to ensure that herbicides are being applied at the correct stage. Some common methods of determining corn growth stage are listed below.

Figure 1: Corn Staging Diagram

Figure 2: Live Plant Corn Staging

 

Corn Height Method  Measure from the soil surface to the highest point of the arch of the uppermost leaf whose tip is pointing down.  Don’t measure to the “highest point” on the plant, which is often the tip of the next emerging leaf above.  Refer to Figure 1/2 on how to correctly determine the height of a corn plant. Corn height varies due to growing and crop management conditions, and is not the most accurate way to stage corn.

Leaf Over Method Count the number of leaves, starting from the lowest (the coleoptile leaf with a rounded tip) to the last leaf that is arched over (tip pointing down). Younger leaves that are standing straight up are not counted.  In Figure 1/2, the corn plant would be at the 4 leaf stage using the leaf over method.

Leaf Tip Method – Count all leaves, including any leaf tips that have emerged from the whorl at the top of the plant. In Figure 1/2, the corn plant would be at the 6 leaf stage using the leaf tip method.

Leaf Collar Method (V-stage) –   Count the number of leaves with visible collars, starting from the lowest (the coleoptile leaf with a rounded tip) and ending with the uppermost leaf with a visible leaf collar. This method is the most common staging system and involves dividing the plant development into vegetative (V) and reproductive (R) stages.  The leaf collar method is generally also the easiest to use, and related better to the physiological stage of the plant and therefore to the effects of herbicides.  In Figure 1/2, the corn plant would be at 3 leaf stage (V3) using the leaf collar method.

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Herbicide Application in Dry Weather – Rules of Thumb

See Dry Weather Weed Control on Manitoba Agriculture website for more details and complete recommendations and cautions.

Dry weather means both weeds and crops shift gears. Weed spectrums can be different,  post-emergent herbicides can  be less effective because weeds may have smaller leaves and/or thicker cuticles (waxy layer) that slows the penetration of herbicides.

Some herbicides withstand dry weather better than others so choose your product carefully. Here are some general guidelines on weed control during a dry period.

1. Remove weeds early.

2. Know your crop stage.

3.  Review the “Effects of Growing Conditions” section of each product in the Manitoba Agriculture Guide to Field Crop Protection to determine likely outcomes.

4. High Daytime temperatures can trigger crop injury in some herbicides.

5. Use full rates of herbicide.

6. Use higher water volumes.

7. Use split applications of broadleaf and grassy herbicides rather than tank mixing if the Guide to Field Crop Protection warns that antagonism can occur.

8. Check the forecast for rain – shallow, stressed crops roots may be impacted by herbicides moving into the root zone.

9. Compare the risk of crop injury to the risk of yield loss due to weed pressure.

 

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Copper Deficiency in Wheat – Symptoms and Cures

Submitted by John Heard, Soil Fertility Specialist, Manitoba Agriculture
Classic symtoms of copper deficiency on soils likely low in copper are:
·         twisted leaf tips 
·         sandy, low OM , high pH soil with known low copper levels 
Or could it just be environmental stress due to frost injury, lack of moisture and drying winds?
A tissue test is needed to confirm copper deficiency as the culprit. 
Studies in Manitoba compared three timings of foliar copper sprays on deficient spring wheat and showed that copper deficiencies and impact on yield can be severe or slight and can vary from year to year.
Timing and application method are important to regain yield! For more information and pictures on copper deficiency, see the full .pdf copy of Copper Deficiency in Wheat
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What Does Seedplaced Fertilizer Injury Look Like?

Submitted by John Heard, Soil Fertility Specialist, Manitoba Agriculture

Already we are hearing of spotty emergence with cereal crops in Manitoba.  Possible culprits may be dry seedbeds, poor quality seed, seed depth, herbicide residues, or seed placed fertilizer injury.Past Prairie studies suggested a 15% stand reduction was tolerable for cereals since surviving plants tillered and filled in the stand.  But maturity is less uniform and is delayed up to 4 days.
How might one confirm seedplaced fertilizer injury?  Close inspection can show a range of symptoms:
1.        Seeds that imbibed water but did not develop any root or shoot
2.       Seeds that developed shoots but no roots
3.       Seeds that developed root and shoot but leafed out below ground
4.       Those that did germinate and emerge (about 44%) were ½ to 1 full leaf stage behind normal seedlings in the low fertilizer strip.
In other crops injury can show as:
Canola – seeds just do not germinate and remain intact.   Fields simply appear to have very poor crop establishment.
Soybeans – stands may be injured, especially with wider row spacing and on sandy soils under dry conditions.
For more information, see the full .pdf document on Manitoba Agriculture Current Crop Topics – What Does Seedplaced Fertilizer Injury look like in Cereals
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2018 Crop Diagnostic School

Registration is now open for the 2018 Crop Diagnostic School in Carman, MB.

School dates are July 10-13 and 17-19.

Topics this year will include insect scouting, dicamba drift, pea disease & soil erosion damage mitigation and others.

For more information see Crop Diagnostic School webpage

Registration can be called into 204-745-5663.

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Volatilization of surface applied urea/UAN

Submitted by: John Heard, Manitoba Agriculture, Soil Fertility Specialist
Surface broadcasting of nitrogen (N) fertilizers has become popular to increase operational efficiency – increasing the speed of seeding and reducing risk of seed injury.  But, in a dry spring with limited rain prospects, growers may choose not to till and avoid further drying out seedbeds.  Then growers must consider the risks of nitrogen volatilization loss and take precautions when risk is high.
Volatilization of ammonia (NH3) from urea or the urea portion of UAN (28-0-0) affected by several factors and can be increased under specific situations.
For more details on the risk factors and ways to minimize losses, see full .pdf 
More topics on soil fertility can be found on Manitoba Agriculture’s Soil Fertility webpages.
 
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Spring Preplant Banded nitrogen Too Hot for Corn in Dry Springs!

Submitted by: John Heard, Manitoba Agriculture, Soil Fertility Specialist
There is no single best way to fertilize corn in Manitoba.  The 4 most common N application methods are spring broadcast and incorporated, fall banded, banded at seeding and preplant banded.
In a dry spring like 2018,  broadcasting and incorporating fertilizer before seeding, risk drying out the seedbed.  Many farmers, especially on clay-textured soils prefer not to disturb their seedbed in the spring and so prefer to fall band their N.  And although spring preplant banding is a very efficient way to place nutrients for a corn crop, it comes with some particular cautions – thinning and seedling injury.  
More detailed information and analysis in full .pdf
More topics on soil fertility can be found on Manitoba Agriculture’s Soil Fertility webpages.
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Can Sidebanded Nitrogen Cause Injury in a Dry Year?

Submitted by: John Heard, Manitoba Agriculture, Soil Fertility Specialist

With a lack of seedbed moisture, there are justified concerns about seedplaced fertilizer injury to canola and other crops.  How safe is sidebanded nitrogen? Research studies by  Dr. Cindy Grant documented considerable canola stand thinning when high rates of sidebanded urea or UAN solution were applied.  Agrotain (AT) served to reduce stand injury, but is no longer supported for this use by the manufacturer. 

Points:
  • Stands were thinned at even modest N rates, on a clay loam soil.  At high rates stands were reduced to 50%
  • Crop growth compensated for reduced stands and generally produced as good a yield as the Agrotain protected stands, except at the highest rate.
For more detailed analysis and discussion on the issue see the full .pdf
More topics on soil fertility can be found on Manitoba Agriculture’s Soil Fertility webpages.
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