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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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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Considerations for Overwintering Corn

The vast majority of corn in Manitoba is in the bin, but what about those few fields that may not be harvested yet? In some cases weather conditions may have made it difficult for farmers to harvest corn in the fall, but some farmers may decide that the corn moisture level and costs associated with drying mean that it is more economical to leave corn in the field to let it dry down naturally over winter.

Just how much dry down can be expected over winter? The amount of drying that occurs in the field depends on the corn maturity, variety, and moisture content, as well as environmental factors such as temperature, humidity, solar radiation, and wind speed. Field drying is extremely slow in the winter, and corn will only dry to about 20 to 21% moisture content. In a typical year, it is expected that corn will dry approximately 11-12% in October, 4-5% in November, and just 2% per month in December and January (Table 1).      

Table 1. Estimated corn field drying

Month

EMC (%)* GDD PET (in.) Estimated Drying (% pt.)
Month Week
Sept 15 250-350 4-5 18 4.5
Oct 16 100-125 2.8-3.5 11-12 2.5
Nov 19 20-30 0.8-1.2 4-5 1
Dec 20 0 0.5-0.8 2 0.5
Jan 21 0 0.5-0.8 2 0.5
Feb 21 0 0.5-0.9 3 0.8
Mar 19 0 1.3-1.6 5 1
Apr 16 50-90 3.2-4.5 16 4
May 14 200-300 6.5-8.5 30 7

*EMC – equilibrium moisture content, GDD – growing degree days, PET – potential evapotranspiration 1EMC is the moisture content to which corn will dry and is based on air temperature and relative humidity

Source: Ken Hellevang, 2009. 2009 Post-harvest tips for later maturing corn. NDSU Extension Service.

Risks of overwintering corn Heavy snowfall during the winter can cause significant amounts of lodging resulting in yield losses. Root and stalk strength should be taken into consideration when deciding if a field should be overwintered. Research conducted at the University of Wisconsin examined corn yield loss during the winter (Table 2).

This researched showed that in 2000, a year with heavy snow cover, yield loss was much greater than in 2001, a year with very little snow cover.  Standing corn may result in more snow catch and slow soil drying in the spring, which could delay planting.

Table 2. Percent yield loss of corn left standing in the field through winter at Arlington, Wisconsin.

Harvest Month
Year Nov Dec Jan Feb Mar Apr
2000 No Loss 45% 58% 59% 65% 38%
2001 5% 5% 9% 18% 7% 10%
Mean 3% 22% 32% 37% 32% 24%

Source: Schneider and Lauer, 2009. Weight risk of leaving corn stand through winter. UW Extension -Team Grains.  http://corn.agronomy.wisc.edu/Teams/TG001.pdf

Corn can be harvested throughout the winter if conditions are cool and there isn’t much snow. If stalks stay standing throughout the winter, and ear drop and wildlife damage are limited, corn can get through the winter without much yield loss.  Yield loss throughout the winter will vary by hybrid and environmental conditions.

If you are planning to over winter corn please contact your local MASC agent.

Submitted by Anne Kirk, Cereals Specialist, Manitoba Agriculture

 

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Why is my Corn Purple?

Many Manitoba corn fields are showing some degree of leaf purpling this spring. Here’s a quick look at why leaves turn purple and what possible causes may be.

 

Leaf purpling is a sign of stress. The leaves are actively producing photosynthates (sugars) but conditions are not allowing normal sugar metabolism or translocation in the plant.  The purple anthocyanin pigment is associated with this sugar buildup in leaf tissue.  The amount of purpling is genetically controlled, so hybrids with more of the purpling genes will appear worse than others, even though all suffer the same stress.

Common stress conditions triggering this purpling are:

  • Warm sunny days but cool nights (4-10oC) – this allows sugar buildup but not metabolism
  • Restricted root growth and development – soil compaction (Figure 1), herbicide injury (such as Edge carryover- Figure 2), standing water.
  • Impaired phosphorus uptake due to insufficient soil phosphorus, lack of phosphorus starter fertilizer (Figure 3) or following non-mycorrhizal crops like canola.
  • Physical injury – recently wind has crimped leaf tips (Figure 4) causing sugars to buildup without being translocated to other growing parts of the plant

Purpling will often dissipate with warmer days and nights and yield loss is slight if any. But severe purpling is a symptom of crop stress, so the astute crop advisor or farmer will exploit it as a visual signal and will investigate the cause so to manage better next year.

 

 

 

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When Should I Start Planting Corn in 2017?

Is it better to plant into cold soils realizing the seed is going to sit there until the soil warms up? Or should corn be planted when soil temperatures are warmer and approaching 10°C?

Planting into cold soils.  Early planting is a component of successful corn production in Manitoba, to maximize yield, obtain high quality and low percent kernel moisture at harvest (which will decrease drying costs), and to ensure the crop is mature before fall frosts.

Cooler soil temperatures can delay the crop’s emergence. Wet conditions added to cold soil temperatures can favor soil pathogen development, increasing seedling disease risks in both germinating seeds and young seedlings. When planting early in the season or when the soil is cold, a planting rate 10% higher than the desired final stand should be considered to compensate for possible increased seedling mortality. As well, when planting into cool soils, other seeding management becomes important, such as good seedbed condition (good soil to seed contact) and planting operations (including planting depth).

For more complete information, visit Manitoba Corn Growers website at http://manitobacorn.ca/plant-corn-wait-warmer-soils/

 

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Frost Prior to Physiological Maturity in Corn

When frost occurs in the early fall before corn has reached physiological maturity (black layer), there is always concern about impact to yields and quality. The stage of crop, minimum temperature reached, relative humidity and duration of cool temperatures all contribute to the impact frost will have on the crop. Generally speaking, a light frost is considered below 0 but above -2°C, where a heavy frost is -2°C and greater.

In corn, grain yield and quality losses become less of a concern the closer the corn is to physiological maturity.

At R5, or the dent stage, crop impacted by either a light or heavy frost will be harvestable but there will be an impact to yield and quality (see Table 1). Within R5, kernels are often staged according to the progression of the milk line, i.e. ¼, ½, ¾. At ½ milk line (R5.5), moisture content of kernels is 35-40% and days to maturity is approximately 13-18 days away.

The stage R6, or physiological maturity, is reached when the milk line disappears and the starch line has reached the base of the kernel. Kernels have reached maximum dry matter accumulation and kernel moisture can range between 30 to 35% (but does vary by hybrid and environment). The formation of the black layer serves as a visual cue that the plant is mature.  At this stage, frost will have minimal impact to yield or quality.

Table 1: Relationship between corn growth stages and calendar days to maturity, yield loss, and other kernel characteristics

Days to Maturity Grain Corn

Source: NDSU Crop & Pest Report – August 8, 2013

A killing frost (-2°C) any time prior to physiological maturity (R6) will kill the entire plant which will stop kernel development. However, if the frost is not a killing frost and the leaves/stalks and husks are still green afterwards, grain filling will continue until maturity.

Picture2

Frost symptoms are water soaked leaves that eventually turn brown. Because it is difficult to distinguish living from dead tissue immediately after a frost event, the assessment should be delayed for a few days after a frost. (Photo by P. de Rocquigny)

Even though the leaves may be impacted, the plants will continue to scavenge nutrients from the remaining plant material to help complete growth and maturity.  However, the crop will still need the necessary heat units to aid in maturity.  If the necessary heat units aren’t received, a premature black layer may form, ending further grain fill, potentially impacting yield but more likely quality.

Submitted by: Pam de Rocquigny, Provincial Cereal Crops Specialist, Manitoba Agriculture

Manitoba Agriculture on Twitter: @MBGovAg
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Manitoba Agriculture website: www.manitoba.ca/agriculture

 

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How Many Days Until My Grain Corn Reaches Maturity?

The 2016 season has seen normal to above normal accumulation of corn heat units (CHU), with a range of 95 to 117% of normal from May 1st to August 14th: Percent of Normal Accumulated Corn Heat Units. So as we inch closer to September, producers start to wonder when their grain corn may reach physiological maturity (R6).  At this stage, kernels have reached maximum dry matter accumulation and kernel moisture can range between 30 to 35% (but can vary by hybrid and environment).  But more importantly, at physiological maturity the grain corn crop will be safe from a killing frost.

The following table was modified slightly from the original table found in NDSU’s Crop & Pest Report August 8, 2013.  The table relates calendar days to corn kernel development and yield in general terms.

Table 1: Relationship between corn growth stages and calendar days to maturity, yield loss, and other kernel characteristics

Days to Maturity Grain Corn

Source: NDSU Crop & Pest Report – August 8, 2013

The ranges listed are fairly large in order to take into account variances in temperature (climate) and the relative maturities of the hybrids grown (genetics).   It is also important to remember that the various plant stages and the duration of those stages can also be influenced by soil fertility, cultural practices (plant populations) and water availability (dry conditions can hasten maturity).

Source:  NDSU Crop & Pest Report August 8, 2013 http://www.ag.ndsu.edu/cpr/plant-science/characteristics-of-late-maturing-corn-08-08-13

Submitted by: Pam de Rocquigny, Provincial Cereal Crops Specialist, Manitoba Agriculture

Manitoba Agriculture website: www.manitoba.ca/agriculture
Manitoba Agriculture on Twitter: @MBGovAg
Manitoba Agriculture on YouTube: www.youtube.com/ManitobaAgriculture

 

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Northern Corn Rootworm – Additional Established Populations Found in Manitoba

Established populations of Northern Corn Rootworm have been found in additional locations, as reported in the most recent Manitoba Insect & Disease Update – August 17, 2016.  The following is provided by John Gavloski, Provincial Entomologist with Manitoba Agriculture.

When corn is grown in the same field for several years in a row, it becomes more susceptible to various potential pests. One such pest is northern corn rootworm (Diabrotica barberi). Until last year only the occasional specimen of northern corn rootworm had been found in Manitoba, and not at levels that appeared to be an established population in a corn field. Last year we did find a well established population in a field in the Souris area. This year we are looking more intensively for them, and have found established populations in corn fields near Morden and Winkler. All fields where they have been found so far have had a long history of consecutive corn being grown in the same field.

This time of year you will see the adult beetles (Figure 1), often on the silks of the corn plants. These adult beetles are generally not of concern, and will lay eggs in the soil of the corn field they are in. When larvae hatch from these eggs the next spring, if there is corn in the field again they will feed on the corn roots. If corn is not in the field they will starve to death. Thus crop rotation is the easiest and cheapest way of dealing with them.

northern-corn-rootworm-on-corn

Figure 1. Northern Corn Rootworm

If anyone finds corn rootworm on their corn, or insects they think may be corn rootworm, we are trying to verify the range of this insect in Manitoba. So samples would be welcome and can be sent to John Gavloski, Manitoba Agriculture, Box 1149, 65-3rd Ave. NE, Carman, MB, R0G 0J0.

Visit the Insect Pages of Manitoba Agriculture’s website at: http://www.gov.mb.ca/agriculture/crops/insects/index.html

 

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Corn Cobs in Tassels – What is the Cause?

Updated from a Crop Chatter post made August 2012

In talking with Morgan Cott, Agronomist with the Manitoba Corn Growers Association, producers are reporting seeing corn cobs in the tassel of plants. Although relatively uncommon, this phenomenon called ‘tassel-ear’ is reported almost every year.  A tassel-ear is very noticeable in the field and is often found on tillers of a corn plant along the edges of a field or in areas of low plant populations. Although it is uncommon to find tassel-ears that develop on the main stalk of a corn plant, it can happen.

Tassel Ear (P.de Rocquigny, 2015)

Tassel-Ear in Corn (Photo by P. de Rocquigny, 2015)

So How Do Tassel Ears Happen? A corn plant has a monoecious flowering habit where the plant has both male and female flowers.  What many may not know is that both flowers are initially bisexual.  During the course of development the female components (gynoecia) of the male flowers and the male components (stamens) of the female flowers abort, resulting in tassel (male) and ear (female) development.

Now every once in a while, the upper flower that typically becomes a tassel instead forms a combination of male and female floral parts on the same reproductive structure. The physiological basis for the survival of the female floral parts on the tassel is likely hormonal, but the environmental “trigger” that alters the hormonal balance is not known.

It has been noted that can be varietal differences where different hybrids produce ears in the tassel and is linked to a particular set of genetics. Ear development in the tassel may also occur when the plant sustains hail or mechanical damage early in its development.  Pollen shed would not have been affected, nor will yields be decreased as a result of this phenomenon.

Submitted by Pam de Rocquigny, Provincial Cereal Crops Specialist, Manitoba Agriculture

For more information on the production and management of corn, please visit Manitoba Agriculture’s website at:  http://www.gov.mb.ca/agriculture/crops/specialcrops/bii01s01.html

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