Field Selection for Corn following Drought
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.
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”?
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
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
