Blog: Agronomy & Extension

Corn Emergence – Early Concerns

mca2022dev on May 25, 2021

SPRING FROST:

Late May consistently brings early frost concerns in all crops. Corn is quite tolerant of temperatures below freezing because the growing point remains below ground until V6 approaches, however, if air temperatures dip below -2oC for more than a few hours, it is possible for the growing point to be damaged. See Is Corn Susceptible to Spring Frosts for temperature and scouting details following a spring frost event.

COLD BANDING:

Due to typical warming, followed by cooling spring temperatures as the corn crop was emerging, at VE and V1 staging it is possible to see cold banding on seedlings. As elongation occurs below the soil surface during warm conditions, a period of chilling can create a few growth issues. Most common is imbibitional chilling injury, which is the twisting or corkscrewing of corn mesocotyl as it is trying to emerge. This is when seed has imbibed (absorbed) the water required for germination and then the soil cools to temperatures below 10oC for prolonged periods. Cold banding is when air temperatures drop to 5 – 10oC and plants close to the soil surface get a yellow band across the leaf tissue. This is not cause for concern, but a common site at this time of year when temperatures bounce around.

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PLANT POPULATION:

As the crop appears to be fully emerged in the late VE staging, it is a great time to do population counts to determine planting accuracy. Not all corn plants may have emerged at this stage, which makes timing appropriate. If the majority of the crop has emerged, a producer should be assessing what percent of the crop remains below the soil surface and why they are behind the rest of the crop. Dry soil, poor seed to soil contact, and consistent planting depth were all planting issues that have to be contended with in extremely dry planting conditions. Go out to the field and do some plant counts now to determine what may have gone wrong just a few weeks ago. Assessing a planting situation at harvest is not the time to learn from mistakes or environmental challenges.

To estimate plant population of emerged crop, determine the length of 1/1,000th acre using the table below (http://corn.agronomy.wisc.edu/AA/A033.aspx). Measure that distance out and count how many plants have emerged. Record the number. Repeat this 10 times at random locations to get an estimated average of final plant population.

1 1000th acre

WEED CONTROL:

The first in-crop herbicide applications can occur at VE in glyphosate-tolerant corn. Due to the dry conditions prior to May long weekend, weed emergence was slow. Following varying rainfalls, weeds will likely be germinating quickly now, so it will be important to stay ahead of weed pressure. See MCA’s Quick Herbicide Reference Guide to see what can be applied and when for certain weed spectrums. It is always recommended to refer to the herbicide label for complete information or Manitoba’s Guide to Field Crop Protection prior to all applications.

Quick Herb Ref Guide

Sunflower Planting Tips

mca2022dev on April 12, 2021

As sunflower planting approaches each spring, a reminder helps producers recall what they are in for. Planting while there is still a risk of frost, is common in May and sunflowers are pretty hardy when faced with spring frosts. First of all, sunflowers will germinate and emerge evenly and quickly when planted into warm soils. They will continue growth at a minimum of 6.7oC, external temperature, but anything colder and growth will be halted until temperatures warm up and the plant knows that it is safe to grow again.

Sunflowers tolerate early frosts fairly well (-3.3oC to -3.8oC) for short periods until the 2-leaf stage (V2). As the plant progresses, it becomes more susceptible to freezing temperatures and up until V6, they can withstand from -1.6oC to -2.2oC for short periods. Remember these points when planting and consider delaying planting if there is a risk of hard frost in the future.

Pre-plant incorporated herbicide applications are very effective in front of sunflower planting. Herbicide choices tend to be limited in sunflowers and planning ahead will give the crop a head start. PPI herbicides often do not control weeds that have already emerged, so a glyphosate application may be necessary, depending on the weed spectrum present.

Final plant populations should be the following:

Confectionery: 14,000 – 16,000 plants per acre

Oilseed:

Birdfood: 22,000 – 24,000 plants per acre

Crush (oil): 22,000 – 23,000 plants per acre

Dehull: 20,000 plants per acre

Planting accuracy is very important in row crops like sunflowers, especially where plant populations are so low. A skip between plants is more area for weeds to inhabit and use what fertilizer they have access to. A double acts as a weed to its nearest neighbour and can get choked out, becoming an unproductive plant. Both scenarios impact yield.

See NSAC’s edition of The Sunflower Production Guide for more growing tips and pest information.

The Sunflower Production Guide

For more information on sunflower planting and tips to achieving high quality seed, register for Hot Topics in Sunflower webinar, hosted by Grainews.

HOT TOPICS REGISTRATION

Crop Germination and Soil Temperatures

mca2022dev on March 31, 2021

Soil temperature is one factor that drives germination and seedling emergence. As we approach seeding in Manitoba, there are a couple of key questions regarding soil temperature that need to be considered:

  • What is the soil temperature at your targeted seeding depth?
  • When should soil temperature be measured?

The following are the minimum temperatures needed for germination to begin in various crop types. Since germination depends on a variety of other factors, these numbers should be considered approximate. However, if soils are too cold, germination will be delayed and cause uneven or poor emergence.

Crop Temperature (°C)
Wheat 4
Barley 3
Oats 5
Corn 10
Canola 5
Flax 9
Sunflower 6
Edible Beans 10
Peas 4
Soybeans 10

Information sourced from: North Dakota State University Extension Service, Alberta Agriculture and Forestry, and Canola Council of Canada.

To get an accurate measure of soil temperature, targeted seeding depth needs to be considered. Your soil thermometer should be placed at that depth, and two measurements should be taken. The first measurement should be taken in the morning (8 am) and the second in the evening (8 pm). The average of these two readings provides a daily average soil temperature. Take readings over a period of 2-3 days to establish a multi-day average and measure several locations in the field to account for variability.

Soil temperature data for various locations across MB can be found here. This is a great resource for getting a general idea of soil temperatures in your area, but of course, in-field measurements are going to give a better picture of what is happening in your field.

Article originally published on Crop Chatter at the following link:

http://cropchatter.com/crop-germination-what-soil-temperatures-are-needed/

Field Selection for Corn following Drought

mca2022dev on January 8, 2021

Corn acres took a hit in 2020 after record planted acres in 2019. Unfortunately, the 400,000+ acres planted in 2019 were droughted, frozen prematurely and over 100,000 of those acres went unharvested by December. It was understandable that after that chaos, corn producers scaled back this past spring. The good news is that, while some areas really struggled with corn this past year, provincial average yield did increase back to a more “normal” yield for Manitoba and it looks as though acres will increase conservatively this year.

Corn seed is certainly booked and secured now, for the most part, but there will be some flex acres on several farms. Some very straight-forward tips for field selection following a relatively dry growing season and a very dry winter to date:

  • Do not plant corn following another deeply rooted crop (eg. sunflower). Instead, select a field that was occupied by a more shallow-rooted crop. Corn is proven to do well after soybeans and some pulse crops.

MARD 2010 2016 yields according to rotation

Yield response of Manitoba crops sown on large (>120 acre) fields of various previous crop (stubble) in rotation (2010-2016 per cent average of relative yields).photo: Manitoba Agriculture and Resource Development

  • If soils remain dry, remember that when planting corn, it will germinate if any moisture is present. If there is only enough soil moisture for germination and not enough to support plant growth and development, a rain will be required to carry the germinated seed any further. Planting timing will be very important, as it always is, but field selection will also be important.

There are several free webinars coming up this winter that can be an invaluable way to remain updated on technologies, innovations, conditions and more, so we strongly recommend you take advantage of the pandemic in this way! It has never been so easy and inexpensive to attend several conferences in one season, across the world! Continue reading this edition of Heads Up for webinars that the Manitoba Crop Alliance is participating in and contributing to!

Frost: When is Corn “Safe”?

mca2022dev on September 8, 2020

A killing frost is a risk at any point during September. Of course, that risk increases the later into the month it gets. Nonetheless, being able to identify maturity staging is key in also knowing the risks of a killing frost prior to physiological maturity.

As seen in the table below, you generally do not want to see a killing frost before 1/2 milkline to avoid major yield losses. Of course, best case scenario is R6, or physiological maturity/black layer, when the grain has filled completely and there will be no penalty to yield or quality (weight).

Table 1: Measurements for each reproductive stage of corn development and how a killing frost would affect yield at that stage.

A killing frost occurs when temperatures dip to 0 Celsius for four hours or -2 Celsius for minutes. However, a killing frost can still occur with temperatures above freezing, especially in low and unprotected areas when there’s no wind. When grain at early to mid-dent experiences a killing frost, yield will be penalized, test weights will be low and these plants will require a long in-field drying period.

A visual inspection of frost-damaged corn should be made the morning after the frost, after the sun has risen and the crop has begun to thaw. At this time, cell contents will begin to leak out and can be seen and smelled. Determine how much of the leaf tissue has been damaged and if the ear shank is frozen. If the shank is frozen, there will not be further movement of sugars to the grain.

For details on how to move forward after a frost during each reproductive stage of corn growth, read this excellent paper from Purdue University.

Fields that have reached the dent stage (R5), days to maturity can be estimated using the chart below from Iowa State University. Estimate a corn field is at ¼ milk line (R 5.25). It will take approximately +/- 30 days to reach physiological maturity (R6), depending on temperature, available moisture and hybrid maturity.

To estimate using current daily temperatures, use the following GDD calculation:

Daily Corn GDD (°C) = ((Daily Max Temp °C + Daily Min Temp °C)/2) – 10 °C

With the following constraints:

If daily Max Temp > 30 °C it’s set equal to 30 °C;

If daily Max or Min Temp < 10 °C, it’s set equal to 10°C.


Table 2: Progression of milk line during R5 with approximate percent moisture, dry matter, growing degree day and days for each substage. Iowa State University.

Depending on current staging, we could be looking at anywhere from 20-30 days until black layer is reached, but a number at the latter end is most likely for many grain corn producers in Manitoba. While we are concerned with how long until each crop reaches physiological maturity and beating the first killing frost, keep in mind the challenges that may arise as a result of drying a wet crop.

“Reaching maturity is important as it means that the crop has maximized the amount of weight that it has packed into its kernels. However, reaching maturity is only part of the issue, as the crop must dry in the field to the point that it can be harvested and be economically dried for storage and marketing. Predicting the rate of drying in the field is more complex than predicting corn development. Factors that affect the rate of field drying include: the initial moisture content of the grain, air temperature, relative humidity, rainfall, dew, wind speed and kernel characteristics.” Joel Ransom, NDSU Crop & Pest Report, September 12, 2019

 

Article written by Morgan Cott, Agronomy Extension Specialist – Special Crops with Manitoba Crop Alliance

Frost Impact on Sunflowers

mca2022dev on September 8, 2020

Frost anytime before the sunflower crop reaches physiological maturity (R9) can cause damage. Once sunflowers reaches the R7 stage (ray petals have dropped, back of head starting to turn yellow), sunflower can withstand temperatures as low as -4° C, but temperature, duration and crop stage will influence the type and amount of damage. A killing frost in sunflowers is considered to be -4 to -5° C for 6 or more hours, as this low temperature for the extended period is required to penetrate the thick layer in the back of the sunflower head and start the dry down process. The following will attempt to describe what happens when a frost occurs prior to the R-9 growth stage.

How Much Time is Needed to Reach R9? Sunflower development is driven by temperature and accumulation of temperatures during the day/night. The formula to convert the daily max/min temperature to a sunflower GDD is ((Tmax + Tmin)/2) – 6.7° C. If the Tmax or Tmin is at or below 6.7° C, then use the 6.7 temperature in the formula instead of the real number. For example, with a 17° C max and a 4° C min temperate = ((17+6.74)/2 – 6.7) = 5 sunflower GDD. From Table 1, the development model indicates it needs 79 ‘sunflower GDD’ to reach R9 from R8 and 157 ‘sunflower GDD’ from R7. On average, throughout September most sunflower growing areas are accumulating on average 7 ‘sunflower GDD’ per day, meaning: R7 (start) to R9 = 22 days R8 (start) to R9 = 11 days

Table 1: Sunflower Growth and Development Model based on GDD from www.ag.ndsu.edu Link to document PDF here Information from this article was provided by Manitoba Agriculture and Resource Development and National Sunflower Association of Canada

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