Author Archives: Pam de Rocquiny

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

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.  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.

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.

Originally Posted on Crop Chatter in September 2016
Last Revised October 2017

The Slow Dry Down of the 2017 Grain Corn Crop

October has arrived and Manitoba grain corn farmers are anxious to start harvesting their 2017 crop. Minimal acres have been harvested (as of October 5, 2017), and fields that have reached maturity are slow in drying down due to cool and rain weather over the past few weeks.

What are normal dry down rates in corn? The best dry down rates are in September. Under good weather conditions from the mid to end of September, dry down rates can vary from 0.75 to 1.0% per day (can be greater in some cases when conditions are warm, sunny and dry, or zero on cool, rainy days!). Into early October, dry down ranges from 0.5% to 0.75% per day. In late October, dry down rate will decrease to less than 0.33% per day. And into November, dry down rate will further decrease to 0.15% per day to negligible amounts.

It is important to keep in mind that moisture loss for any particular day may be higher or lower depending on the temperature, relative humidity, sunshine, wind or rain conditions that day.

Potential Yield Loss. If the crop remains standing in the field, there is the potential for yield loss. The extent of loss will depend on many factors, including stalk strength, ear drop or wildlife damage. Ear drop will vary by hybrid and environmental conditions as well as the amount of grain on the ear (smaller ears should stay attached better than larger ears).  Stalk strength should also be considered when evaluating harvest timing (and this includes assessments of stalk rots). Compromised stalk strength could lead to increased stalk breakage, resulting in lost yield.

As corn matures and dries down, it will be a more common sight across Manitoba in the coming weeks to see farmers harvesting their grain corn.

Originally Posted on Crop Chatter in November 2016
Last Revised October 2017

Weather & Hybrid Characteristics – Their Roles in Grain Corn Dry Down

Grain corn in Manitoba is maturing quickly, and as seen on Twitter, some of the earliest planted fields have reached physiological maturity. Normal plant processes and weather conditions are the major influences on grain dry down, although hybrid characteristics can also play a role. As corn harvest approaches, a quick review of the facts concerning grain drydown might be helpful.

Grain drydown can be separated into two stages: the grain fill period and after physiological maturity.

Drydown During Grain Fill. The grain fill stages (R1 to R5) begins at flowering and is completed at physiological maturity. Grain filling is characterized by the rapid accumulation of dry matter in the kernel and the rapid movement of water out of the kernel.  Decreases in kernel moisture occur from a combination of actual water loss (evaporation) from the kernel surface and the accumulation of dry matter.  The corn plant uses “internal plumbing” to move water out of the kernel since water movement out of the kernel is regulated by how much dry matter is being forced into the kernel.  The corn plant is much more efficient in removing water from the kernel using its “internal plumbing” instead of physical evaporation through the kernel surface.

Drydown After Physiological Maturity. Physiological maturity (R6) occurs when kernel moisture is at approximately 30 to 32% (but can vary).  At this stage of growth, a layer of cells at the base of the kernel dies and turns black (hence black layer), the “internal plumbing” is therefore disconnected, and a barrier is formed between the kernel and the corn plant.  For this reason, post-maturity grain moisture loss occurs primarily by evaporative loss from the kernel itself. Research many years ago established that post-maturity moisture loss through the kernel connective tissues (placental tissues) back to the cob is essentially non-existent.

Role of Weather. As moisture loss after maturity is due to physical evaporation, field drying of mature corn grain is influenced primarily by weather factors, especially temperature and humidity.  In simple terms, warmer temperatures and lower humidity encourage rapid field drying of corn grain.

Because moisture loss is greatest just after physiological maturity, both because the weather is usually warmer and because wet kernels lose water more easily, it stands to reason that a corn crop that matures earlier in the season will dry down faster than a crop that matures later in the season.  However, it is important to keep in mind that grain moisture loss for any particular day may be quite high or low depending on the exact temperature, humidity, sunshine, or rain conditions that day. It is not unheard of for grain moisture to decline more than one percentage point per day for a period of days when conditions are warm, sunny and dry. By the same token, there may be zero dry down on cool, rainy days.

Role of Hybrid Characteristics.  A number of hybrid characteristics can influence the rate of dry down, but to a lesser degree than weather. However, when weather conditions are not favorable for rapid grain dry down, hybrid characteristics that influence the rate of grain drying become more important.  The relative importance of each trait varies throughout the duration of the field dry down process and, as mentioned earlier, is most influential when weather conditions are not conducive for rapid grain drying.

  • Husk Leaf Number. The fewer the number of husk leaves, the more rapid the grain moisture loss.
  • Husk Leaf Thickness. The thinner the husk leaves, the more rapid the grain moisture loss.
  • Husk Leaf Senescence. The sooner the husk leaves senesce (die), the more rapid the grain moisture loss.
  • Husk Coverage of the Ear. The less the husk covers the tip of the ear, the more rapid the grain moisture loss.
  • Husk Tightness. The looser the husk covers the ear, the more rapid the grain moisture loss.
  • Ear Declination. The sooner the ears drop from an upright position to a downward position, the more rapid the grain moisture loss.
  • Cob Diameter. The narrower the cob diameter, the more rapid the grain moisture loss.
  • Kernel Type.  Flint-dent kernel types tend to dry down slower in comparison to dent kernel types due to the harder nature of the kernel.

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

Did You Plant Non-BT Corn & Not Spray for ECB? Researchers Need Your Fields!

European Corn Borer Larvae – Photo Credit: Manitoba Agriculture

Dr. John Gavloski with Manitoba Agriculture is collecting European Corn Borer (ECB) larvae to have populations tested for potential resistance to Bt toxins. John will send the larvae to Ontario for this resistance monitoring study.

John Gavloski is looking for fields that were planted to a non-Bt corn hybrid and preferably not sprayed for ECB. If you have a field that meets those requirements, please email John at john.gavloski@gov.mb.ca or call 204.745.5668.  You can also call the MCGA office at 204.745.6661 and we will forward the information to John.

 

Estimating Grain Corn Yields

 

The time of year is approaching where yield estimates can be done on grain corn.  Remember that grain corn yield is a function of the number of ears per acre, number of kernels per ear, and the weight per kernel.   Using the yield component method that was developed at the University of Illinois, yields can be estimated as early as the milk stage of development.

 

Calculating Estimated Grain Corn Yield:

Step 1.  Ear Number  – Using a row length equal to 1/1000th acre (row width 30 ” = 17′ 4″; row width 36 ” = 14′ 6”), count and record the number of ears in the length of row that are harvestable.

Step 2. Average Number of Kernels per Ear – Pick 3 representative ears and record the number of complete kernel rows per ear and average number of kernels per row.  Multiply each ear’s row number by its number of kernels per row to determine total number of kernels for each ear.  Calculate the average number of kernels per ear by summing the values for all the sampled ears and dividing by the number of ears.

Note – Don’t count the extreme butt or tip kernels, but rather begin and end where you perceive there are complete “rings” of kernels around the cob.  Do not count aborted kernels.

Step 3. Estimate yield by multiplying the ear number by the average number of kernels per ear, then dividing the result by 90:  Yield (bu/ac) = (ear number) x (average # of kernels per ear) / 90.

Note:  The value of 90  is a “fudge factor” for kernel weight and it represents the average number of kernels (90,000) in a bushel of corn at 15.5% grain moisture.  If grain fill conditions have been excellent (larger kernels, fewer per bushel), use a lower value (80).  If grain fill conditions have been stressful (smaller kernels, more per bushel), use a larger value (100).

Here’s an example:  Field has 30” rows.  You counted 24 ears (per 17’ 5” length of row).  Sampling three ears resulted in 480, 500 and 450 kernels per each ear, where the average number of kernels per ear would be (480 + 500 + 450) divided by 3 = 477.  The estimated yield for that location in the field would be (24 x 477) / 90, which equals 127 bu/ac.

Remember that yield estimates are only as accurate as the number of samples taken so repeating this exercise in several areas of a field will improve accuracy.  Since corn is in the early grain filling stages, water availability, insects, weeds, diseases, and other factors can still affect seed fill and therefore final yields.  However, as the plant approaches maturity, environmental stresses have less impact on final yield so yield estimates made that are closer to maturity should be more accurate.

Originally Posted on Crop Chatter in August 2012
Last Revised August 2017

 

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.

DSCN1711

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

FullSizeRender

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.

References:

Nielsen, R.L. (Bob). 2008. Corn Ear Damage Caused by Bird Feeding. https://www.agry.purdue.edu/ext/corn/news/timeless/birddamagedears.html

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: http://www.gov.mb.ca/agriculture/weather/pubs/percent-normal-chu.pdf.

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

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

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.

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).

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 1, 2017