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Bird Damage in Corn

It is not uncommon at this time of year to hear of blackbird damage. Birds will often feed on developing ears in corn fields following pollination and early in the grain filling period.

What Does Bird Damage Look Like? Typical symptoms include missing or damaged kernels on the cobs.  In the first photo, shredded husks is the key symptom in identifying birds as the culprit.  Secondary damage can result from ear rots as kernels eaten by the birds will often turn brown or black once the ear rots begin infecting the damaged tissue.


Corn Ear Damage Caused by Birds. 2014. Photo Courtesy of Earl Bargen, Manitoba Agriculture 


Corn Ear Damage Caused by Birds. 2014. Photo Courtesy of Lionel Kaskiw, Manitoba Agriculture

R.L. Nielsen in his article ‘Corn Ear Damage Caused by Bird Feeding‘, indicates birds, especially large flocks, can cause quite a bit of damage. The most damage occurs along field edges or by wooded areas such as bush, but damage can extend throughout an entire field.

Preference for one hybrid over another? It is not unusual for birds to prefer one hybrid over another, although the reasons are unclear.  Perhaps it can be attributed to birds being able to detect slight differences in kernel maturity or other kernel characteristics between hybrids. Bollinger and Caslick (1985) indicated that kernel maturity (as measured by date of silking) was the most important factor in determining the level of blackbird damage to corn.  Within a field, the degree to which the husk leaves extended beyond the tip of the ears (husk coverage) was also strongly correlated with the severity of damage.

Hybrid specific feeding has been observed in past corn committee trials, and not only with birds but with other animals such as raccoons.  Amazingly, the animal can pick out a hybrid within each replicate of the trial without damaging other hybrids.

Control? As seen in other crops such as sunflowers, damage from blackbirds can be an on-going, variable, and uncontrollable natural phenomena with no practical means of management or mitigation. Current scare techniques such as cannons offer little relief as the birds quickly become accustomed to the sounds.


Nielsen, R.L. (Bob). 2008. Corn Ear Damage Caused by Bird Feeding.

Bollinger, Eric and James Caslick. 1985. Factors Influencing Blackbird Damage to Field Corn. J. Wildlife Mgmt 49(4):1109-1115.

Originally Posted on Crop Chatter in October 2014
Last Revised August 2017

How Many Days Until My Grain Corn Reaches Maturity?

The 2017 season has seen normal to above normal accumulation of corn heat units (CHU) in most areas from May 1st to August 13th:

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

Originally Posted on Crop Chatter in August 2016
Last Revised August 2017

Got purple corn?

Submitted by: John Heard, Crop Nutrition Specialist, Manitoba Agriculture

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.

Figure 1. Leaf purpling resulting from soil compaction and poor rooting.

Figure 2. Leaf purpling due to root stress from Edge residue.


  • Impaired phosphorus uptake due to insufficient soil phosphorus, lack of phosphorus starter fertilizer (Figure 3) or following non-mycorrhizal crops like canola.

Figure 3. Slight leaf purpling from neglecting starter phosphorus fertilizer.

  • Physical injury – recently wind has crimped leaf tips (Figure 4) causing sugars to buildup without being translocated to other growing parts of the plant

Figure 4. Purpling of mechanically damaged leaf tips.

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.

Floppy Corn Syndrome

A few cases of “floppy corn” in various areas of the province have been reported.  What is “floppy corn” and why does it happen?

If dry surface soil and/or hot, dry weather conditions exist, several sets of nodal roots may fail to form, resulting in “rootless corn”.  Affected plants must depend on the seminal roots and mesocotyl for nourishment when normally the seminal roots have already taken a backseat to the nodal root system.

Before rootless corn is evident, corn plants may appear vigorous and healthy.  The problem often becomes evident when corn is subjected to strong winds, which result in plants falling over because there is a limited number or no nodal roots supporting them. The leaning or lodging plants are often referred to as “floppy corn” (see Figure 1: Floppy Corn Syndrome) and it is generally observed in plants from about the three leaf stage to the eight leaf stage of development.

When affected plants are examined, the nodal roots appear stubby, blunt, and unanchored to the soil (see Figure 2: Nodal Roots). The root tips will be dry and shriveled.

Because several sets of roots may not have formed below-ground, the crown may “appear” to be at or above the surface (see Figure 3: Crown located above soil surface).  Leaning and lodged plants may also be wilted.

Rootless corn problems are usually caused by weather related conditions that coincide with development of the nodal root system. However, rootless corn can also be caused by shallow seeding depths that result in nodal root initiation beginning at the soil surface rather than at the usual ¾ inch depth.

What Can Be Done?

The best thing for “floppy corn” is adequate rainfall which will promote crown root development and help plants to recover.  Cultivation to throw soil around exposed roots may also help the corn’s recovery.  Since affected corn is likely to be vulnerable to potential lodging problems at maturity, it should be harvested as soon as grain moisture conditions permit.

Originally Posted on Crop Chatter in June 2013

How to Determine Leaf Stage in Corn

Knowing what leaf stage your corn crop is at is extremely important since post emergent herbicides can only be applied to corn up to the label-specified leaf stage. Therefore both farmers and agronomists need to accurately stage corn plants.

Herbicide labels often refer to plant height, crop growth stage (leaves or collars), or both when discussing corn growth stage limits for the application of postemergence herbicides. Below is a review of some common methods for determining growth stage. It is important to know which method the herbicide manufacturer is using to indicate correct herbicide application timing. For each method, the stage of the corn plant in Figure 1 will be determined.

Figure 1: Staging a Corn Plant

Leaf Collar Method (V-stage).  The leaf collar method is generally the easiest to use. It also relates better to the physiological stage of the plant and thus to the effects of herbicides. Staging by the leaf collar method is done by counting the number of leaves with visible collars, beginning with the lowermost, short, rounded-tip true leaf and ending with the uppermost leaf with a visible leaf collar . Collars are not visible until the leaves are developed enough to emerge from the whorl. In Figure 1, the corn plant would be at 3 leaf stage (V3).

Corn Height Method.  To determine corn plant height, 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 on how to correctly determine the height of a corn plant.

Both environmental and management conditions can have a great impact on the height of a corn plant. In cool, wet springs, corn often grows more slowly from a height standpoint but it is still advancing physiologically. A delayed seeding date, differences in tillage, and differences in soil type can also have a pronounced effect on plant height but relatively little effect on the stage of vegetative development. Hybrid can also have an effect on plant height as shorter-season hybrids tend to produce shorter plants. Because corn height varies a great deal due to growing and crop management conditions, it is not the most accurate way to stage corn plants.

Leaf Over Method.  The leaf over method is a common way of measuring leaf number. The leaf over method counts the number of leaves, starting from the lowest one (the coleoptile leaf which has a rounded tip) up to the last leaf that is arched over (tip is pointing down). Do not count leaves younger (inside) than this one, even though they are present in the whorl. In Figure 1, the corn plant would be at the 4 leaf stage.

Staging Corn with Severe Leaf Damage.  Dead leaf tissue will not resurrect itself and will eventually slough off as the plants continue to grow. The question is whether the leaf stage of a recovered plant begins anew with the healthy leaves or whether the dead leaves (which may no longer be visible) should be counted. In other words, should a 3-leaf plant that has lost 2 leaves to frost injury now be considered a 1-leaf plant?

The simple answer is: If corn was a 3-leaf plant prior to the frost, physiologically it still is a 3-leaf corn plant after the frost, no matter how many lower leaves are damaged, dead, or otherwise missing.

Last Revised: June 7, 2018


Dry Soil Conditions and Corn Establishment

In Manitoba, precipitation from November 1, 2017 to April 29, 2018 has been below normal for many areas (see figure – .

There are a number of great resources and articles by experts in other areas of Canada and the United States. The following is an article by Dr. Joel Ransom, Extension Agronomist for Cereal Crops with North Dakota State University, on the impact of dry soil on corn germination and emergence.

The following is an excerpt from the article:

For most soils, 0.5 inches of rain (sandy soils slightly less) is needed in order for moisture to move to a 2 inch depth (the seed zone) in dry soils. Other factors can also affect germination and emergence when soil moisture is marginal. Poor soil-seed contact can restrict the corn seed from extracting enough moisture from the soil to germinate. Crop residues that touch the seed can similarly impede the movement of water to the seed. Occasionally, fertilizers placed with the seed inhibit germination due to their salt effect being more pronounced in dry soils.

Moisture in the top two inches of soil is also required for nodal root development. Nodal roots develop from the crown, which establishes about ¾ inch below the soil’s surface, regardless of planting depth. These roots initiate soon after the V1 stage and rapidly develop to become the primary means by which the plant acquires water and nutrients by the V3 stage. If the soil remains dry around the crown for an extended period during early vegetative growth, however, nodal roots will not develop and when plants obtains sufficient size, they flop over (accompanying photo). Though this phenomenon, called the floppy or rootless corn syndrome is found occasionally in areas of the field with lighter soils or where there is compaction or shallow seeding, it may be more widespread during seasons of limited early rainfall like this year.

The complete article appears in the NDSU Crop & Pest Report – June 1, 2017 edition and is available here: Dry Soils and Poor Corn Emergence.

Last Revised: June 2017

Sandblasting Injury in Corn (& Cereals)

In Manitoba, it is not uncommon to see extremely windy conditions early in the season.  Strong winds may result in sandblasting injury in young and emerging corn crop, as well as other crops such as cereals.  Sandblasting injury is caused by winds impacting soil particles against the plant leaves.  Light, sandy soil areas are the most common areas of sandblasting in a field.

Symptoms include:

  • Small abrasions on leaves caused by blowing sand, which are often copper-tone in color
  • Shredding of leaf tissue, making them prone to desiccation
  • Plants may be cut off at the soil surface in severe cases.

In corn, the growing point remains below ground until approximately the V5 leaf stage, so if only leaves are affected the plant should recover without substantial yield loss.  In cereal crops, the same principle applies. Favorable weather including warm temperatures and rainfall will promote development of new leaf growth.  However, if the growing point in either crop type has been impacted, reduced stands will likely result.  So the key is to keep scouting for the next few weeks to assess the full impact.

Goss’s Wilt in Corn
In corn, another point to keep in mind is plants that are damaged by hail, wind, or sand-blasting are susceptible to Goss’s Wilt infection as the bacteria can infect corn throughout the growing season and can enter through the wounds caused by sand-blasting.

As you are scouting for Goss’s Wilt throughout the season, focus your attention on fields that are:

  • planted to a Goss’s susceptible hybrid,
  • have a history of Goss’s Wilt,
  • have surface corn residue, and
  • may have been injured by severe weather.

Initial symptoms of Goss’s Wilt include water-soaked lesions on the leaves later accompanied by “freckling”. Bacterial ooze may also occur on the lesion, giving it a wet or greasy appearance. When the ooze dries, it leaves a shiny residue on the surface of the lesion.  More information and photos can be found at Goss’s Wilt Distribution in Manitoba.

Last Revised May 2017

Determining Final Plant Stands in Corn

Corn producers are encouraged to take the time and evaluate their final plant stands as plants emerge and develop through early leaf stages.

Did You Hit Your Plant Stand Target or Miss it? 

To determine plant population or stand, count the number of corn plants in a row length equal to 1/1000 acre. Multiply that number by 1000 to get the number of plants per acre.  Do this several times in a field to get a representative sample.

  • In a 30-inch row spacing, count the plants in a 17’4″ row.
  • 20-inch row spacing, count the plants in a 26’1″ row.
  • 22-inch row spacing, count the plants in a 23’8″ row.

Now compare the final plant populations achieved to what you intended to plant, i.e. calculate your attrition losses.  If losses range up to 10% or more, investigate the reasons.  Was germination impacted by cold, wet soils? Did insects like wireworms or cutworms impact final plant stands?  Identifying the cause(s) behind the losses is important.  It can help determine whether changes in your planting operation or agronomic decisions may improve the odds of good stand establishment in the future.

Last Revised: May 2017

Uniform Plant Spacing in Corn = Greater Yield Potential!

Corn producers should evaluate their uniformity of plant spacing.  A well-tuned planter operating at a reasonable speed should optimize uniform plant spacing within a row. Planting at high speeds with a poorly maintained planter can result in a large number of doubles (two-plant hills) and skips (missing plants), both resulting in lost yield potential for the field.

There is a quick and easy way to determine yield potential yield loss from non-uniform plant spacing.

#1. Take a 20-ft tape measure and lay next to the row of plants to be evaluated for uniformity of spacing (see figure below).

#2. Record the location within each row in inches of each corn plant (up to 20 ft).

#3. Enter the data into a spreadsheet where average plant spacing and standard deviation (SD) can be calculated.  See below for an example.  Yield loss due to non-uniform plant spacing is estimated using the following equation:

yield loss = (present plant spacing SD – 2.0) x (4 bushel per acre per inch of SD improvement)

So what should producers be aiming for?  Doerge and Hall (2000) previously found a standard deviation of 2 inches is the best spacing uniformity that a commercial producer can typically expect to obtain under normal production planting conditions. They found that if the SD is greater than 3, then the planter needs calibration. If the SD is less than 3, then calibration is not required.

The entire article titled “Estimating Corn Yield Losses from Unevenly Spaced Planting” by Carlson, Doerge and Clay can be found at:

Adapted from CropChatter May June 2014; Last Revised May 2017

Uniform Emergence in Corn Critical to Yield

Ensuring corn emerges uniformly is the first step in maximizing yield potential.

Why Corn Emerges Unevenly.  The most common reason for uneven corn emergence is soil moisture. Soil moisture in the seed zone can differ because of variations in soil type, topography, and uneven distribution of moist and dry soils due to secondary tillage. Cloddy seedbeds caused by working the ground too wet can result in poor contact between seed and soil, allowing some seeds to germinate while others are too dry.

Another factor affecting corn emergence is soil temperature. Seed depth soil temperatures can vary if crop residues aren’t evenly distributed, if seed depths vary, and if soil within fields vary in type and topography. Corn may also emerge non-uniformly because of variable soil crusting, herbicide injury or because of insects or diseases.

Impact on Grain Yields. Competition from larger, early-emerging plants will decrease the yield of smaller, later-emerging plants. Research out of the University of Illinois examined the effect of non-uniform emergence on grain yield. Plots were hand planted and consisted of uniformly planted plots on three separate dates, and various combinations with certain parts of the plot seeded at a later date to simulate delayed emergence.

When looking at within row emergence patterns, a definite yield decrease was seen when plants emerged later than their neighbor (see Table 1).

Table 1: The effect of planting date and uniformity of emergence within row of corn yield.

(Average of 7 locations in Illinois and Wisconsin from 1986-1987).  Source: Nafziger, Carter and Graham, Crop Science 31: 811-815 (1991).

The treatment 3E:1M consisted of one plant in every four being planted 10 days later. The result is a decrease in yield of 12 bu/acre (176 bu/ac) compared to the plots where all plants emerged uniformly on the early planting date (188 bu/ac). This yield loss was similar if the entire stand was delayed 10 days. Similar results are seen when emergence (planting) was delayed by 3 weeks, where a decrease in yield of 20 bu/ac was seen compared to the plots where all the plants emerged uniformly on the early planting date.

What to Look at Before & After Planting. Careful planter preparation and pre-planting management are crucial factors affecting uniformity of emergence. On the planter, factors to check include:

  • opening discs are aligned
  • ensure planter is level
  • properly adjust seed firming wheels
  • proper seed depth placement.

Pre-planting management factors to check include:

  • residue – is it bunched?
  • ensure field is not too rough

During planting, also ensure speed is suitable for the field conditions. If field conditions are poor and planting is done at a higher speed, the planter bounce can causing seed depth misplacement. So if one seed out of four is placed out of moisture and it doesn’t rain for a week, a yield decrease may result.

After the crop is up and growing, examine to see if the corn plants are all at the same leaf stage. If there are plants that are one to two leaves behind their neighbors, it could indicate problems with emergence. Nothing can be done for this growing season but knowing what caused it can help with future corn seeding operations.

Adapted from CropChatter Post May 2015; Last Revised May 2017