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.

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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

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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
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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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Why am I seeing Tillers in my Corn?

I have been receiving a few calls over the season regarding tillering in corn. So I figured a Crop Chatter post based on an article I wrote back in 2005 would be good to answer some questions. Is it only due to plant populations? What could be other causes? What effect will tillering have on crop growth and yield potential?

What are Tillers? And What Causes Them?  Tillers are lateral branches that form at below ground nodes. Although tiller buds form at each below ground node, the number of tillers that develop is determined by plant population and spacing, soil fertility, early season growing conditions, and the genetic background of the hybrid.

  • Plant Population: Many hybrids will take advantage of available soil nutrients and moisture by forming one or more tillers where stands are thin in the row or at the ends of rows. However, excessive tillering may indicate problems with stand density and distribution. If tillering is associated with row gaps and less than optimal plant populations, these are the conditions which need to be corrected to ensure optimal yields.
  • Soil Fertility: Tillers are most likely to develop when soil fertility and moisture supplies are ample during the first few weeks of the growing season. They are usually visible by the 6-leaf stage of development.
  • Genetics: Hybrids with a strong tillering trait may form one or more tillers on every plant even at relatively high populations if the environment is favorable early in the growing season. If a particular hybrid shows excellent yield potential and also produces extensive tillering under some growing conditions, it should not be avoided.
  • Weather Conditions: Hail, frost, and flooding injury that destroy or damage the growing point early in the growing season can also result in tiller development and non-productive plants.

What is the Effect on Yield Potential? When farmers see extensive tillering in their corn hybrids, they often express concern that the tillering will have a detrimental effect of crop performance (that the tillers will “suck” nutrients from the main plant and thereby reduce yields). As a result, tillers are often referred to a “suckers”. However, research has shown that tillers usually have little influence on grain yields and what effects they do have are generally beneficial. Recent studies have found that there is little movement of plant sugars between the main plant and tillers before tasselling.

After silking and during grain fill, substantial amounts of plant sugars may move from earless tillers to ears on the main plant. When there are ears on both the tiller (often called ‘tassel-ears’) and the main plant, little movement of plant sugars occurs. The main plant and tillers act independently, each receiving sugars from their own leaves. The ‘tassel-ears’ that tillers may produce, therefore have no impact on the ear development of the main plant as was once thought and don’t contribute to yield.

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

Manitoba Agriculture website: www.manitoba.ca/agriculture
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Manitoba Insect & Disease Update – Issue 10: July 20, 2016

The Manitoba Insect and Disease Update is now posted at: http://www.gov.mb.ca/agriculture/crops/seasonal-reports/insect-report-archive/insect-report-2016-07-20.html

Some highlights from the update:

Insects:

  • Pea aphid levels are still a concern in some pea fields, although many fields will be getting to the stage where management would no longer be economical.
  • Aphid levels have dropped in many cereal fields where previously levels had been increasing. High levels of natural enemies have been noted in some of these fields, and some intense rains may have also contributed.
  • In some areas of Central and Southwest Manitoba, greater than 90% of the wheat midge are expected to have emerged. In many areas of Manitoba about 50 to 90% of wheat midge are expected to have emerged. A reminder that wheat that has already produced anthers is no longer susceptible to feeding by wheat midge. Even if adults are still active in these more advanced fields, the larvae will not feed on the grain.
  • Egg masses of European corn corer are starting to be noted in some fields of corn. So far there are no reports of high levels, but now is the time to be checking fields for the egg masses.
european-corn-borer-egg-masses

Figure 1. Egg masses of European corn borer.

Plant Pathogens:

  • Some infections of blackleg in canola and fusarium head blight in cereals have been reported.
  • A few cases of loose smut in barley were also reported.
  • Two positive identifications of Goss’s Wilt in corn were made. The positive identifications were made based on immunostrips and/or polymerase chain reaction (PCR) assays.

Submitted by: John Gavloski, Entomologist & Pratisara Bajracharya, Field Crop Pathologist, Manitoba Agriculture

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Hail Damage in Corn & the Impact of Bruising and Stalk Damage

Hail in the recent days have impacted some corn acres in Manitoba.  In an earlier Crop Chatter post (Assessing Hail Damage in Corn), typically yield reduction due to hail damage is a result of leaf loss.

However, there can be an impact if hail injured the stalk (see Figure 1).

Bruising of Corn Stalk from Hail - June 2016 (Photo by P. de Rocquigny)

Figure 1: Bruising of Corn Stalks from Hail (Photo by P. de Rocquigny, June 2016)

The following information is adapted from articles “Recovery From Hail Damage to Young Corn” by R.L. Nielson of Purdue University and “Differentiating Superficial and Deeper Hail Damage” by C. Shapiro of Haskell Ag Lab.

Q: What will be the impact to yield? The eventual yield effects of severe bruising or damage of the stalk tissue itself can be quite difficult to predict. Consequently, it can be difficult to determine whether to count severely bruised plants in assessing plant stands. Observations reported from an Ohio on-farm study suggest that bruising from hail early in the season does NOT typically result in increased stalk lodging or stalk rot development later in the season.

Early season bruising of stem tissue may, however, have other consequences on subsequent plant development; the occurrences of which are hard to predict. If the plant tissue bruising extends as deep as the plant’s growing point, that important meristematic area may die; thus killing the main stalk and encouraging the development of tillers. If the plant tissue bruising extends into the area near, but not into, the growing point; subsequent plant development may be deformed in a fashion similar to any physical damage near the hormonally active growing point.

Q. How can I tell how badly damaged corn may be from bruising? Bruising is difficult to determine. You can make an initial assessment about a week to 10 days after the storm. Peel the sheaths away from the stalk and determine if the damage has actually penetrated the stalk. The outer stalk (rind) is strong and can resist some damage. However, if the stalk has brown areas, that may indicate stand problems later in the season.

Cutting the stalk vertically from node to node will help determine the extent of damage (Figure 2). Brown areas in the pith where the hail hit indicate the potential for problems later in the season. The stalk in Figure 2 does not show any bruising from the pith. These areas will disrupt the movement of fluids in the plant and reduce growth. Bruised plants that show stalk damage in the pith should probably be considered as missing plants in yield calculations.

Split corn stalk

Figure 2. Cut the corn stalk vertically from node to node to help determine the extent of damage. Source: Differentiating Superficial and Deeper Hail Damage

 

Remember that estimating yield loss due to hail is only an estimate, particularly if the damage is not severe and depending upon growth stage of the plant when the hail event occurred.  The remainder of the growing season will help determine final yields.  Please contact your hail insurance provider for their procedures in assessing hail damage as they may be different that what has been provided here.

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

Manitoba Agriculture website: www.manitoba.ca/agriculture
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Preplant Banding Ammonia & Urea in Corn

A very efficient placement method for rates of nitrogen that can’t be placed at seeding is the preplant band. Despite the popularity of direct or one-pass seeding this is still used in crops where some pre-plant tillage is done – like for corn.

The past few years, more often in dry springs, I have seen stand thinning using this practice. When the corn row falls directly over the N band (be it ammonia or urea), seedlings are injured, stunted and sometimes killed. This leaves a repeating pattern in an angle across the field.

There are some standard guidelines if using this practice:

  • Stand thinning may occur where the seed row intersects the N band. Band N on an angle so that it intersects just a short length of row.  OR if the injection placement can be controlled with accurate GPS guidance positioning technology, split with the future corn row.  Six inch separation should be sufficient.
  • Place the nitrogen deep. Banding at 3” depth may be sufficient for slot closure and N retention in the soil – but this will only be an inch or so below the seed. The original guideline calls for 4” vertical separation of injection point and seed.
  • The toxicity will be worse under dry conditions and on sandier soils.
  • Waiting a certain period of time offers only a slight increase in safety.  Injury can still occur even if planting is delayed for a considerable period of time.
  • Increasing plant populations to account for such thinning will not eliminate the appearance of gaps in the row.

Figure 1 is of corn thinning over a preplant urea band.

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Figure 1: Corn thinning over a preplant urea band (Photo by John Heard, Manitoba Agriculture)

Figure 2 is of corn seedling based on their proximity in intersecting the shallow placed preplant ammonia band.

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Figure 2: Impact of shallow placed preplant ammonia band on corn seedlings (Photo by John Heard, Manitoba Agriculture)

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

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Safe Liquid Fertilizer Rates for Corn

Much of Manitoba’s corn receives liquid phosphorus as a starter in the seedrow.  But we cannot apply sufficient amounts with the seed to meet full crop removal (about 44 lb P2O5/ac for a 100 bu/ac crop).  The safe amount of seed placed fertilizer depends upon soil type, moisture, row spacing and seed furrow opening.  Ontario guidelines base the safe rates of fertilizer on N and K content of the starter fertilizer.  For 30 inch rows no more than 10 lb N/ac should be seedplaced – enough to provide 34 lb P2O5/ac of 10-34-0 liquid fertilizer or 8.5 US gal per acre.  But based on South Dakota  studies such rates could cause stand thinning of 4-9% depending on soil moisture and texture. Most farmers will not be pushing starter rates this high as they should have the bulk of their P needs met through a safer placement strategy.

More on these safe rates of fertilizer is posted on Manitoba Agriculture’s website at: http://www.gov.mb.ca/agriculture/crops/soil-fertility/print,safe-rates-of-seed-placed-phosphorus-for-manitoba–narrow-row-and-row-crops.html

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

 

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Safe Rates of Seed Placed Fertilizer – Cereals & Canola

A reminder that if seedbeds turn dry, the safety margin shrinks when applying seed placed fertilizer.  Seedburn can result from ammonia toxicity and/or salt content of fertilizers.

For nitrogen, our Soil Fertility Guide provided safe guidelines for seed placed urea on cereals and canola across a range of soil types and seed-fertilizer configurations.  With the increased popularity of narrow seed and fertilizer spreads with disk drills, the safe rates are reduced.  For example, safe urea rates for cereals vary from 10 to 25 lb N/ac going from sand to clay soil using disk openers on 6” row spacing.  These guidelines are for moist soil and should be reduced by 50% if seedbed moisture is lower when weather is hot and windy.

The safe rates of seed placed phosphorus depends on the crop, with cereals being quite tolerant compared to soybeans, dry beans and canola.  With a disk drill as described above, cereals can tolerate 50 to 60 lb P2O5/ac as mono ammonium phosphate while rates would be 20 lbs/ac for canola and less for beans.   If there greater seedbed utilization (i.e. narrower rows or a wider seedrow with less fertilizer concentration) rates could be more liberal.

More on these safe rates of fertilizer is posted on Manitoba Agriculture’s website at: http://www.gov.mb.ca/agriculture/crops/soil-fertility/print,safe-rates-of-seed-placed-phosphorus-for-manitoba–narrow-row-and-row-crops.html

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

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