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
Manipulator PGR Available for Use on Barley
Starting this growing season, plant growth regulator (PGR) Manipulator will be available for use on barley in Canada. The PGR, which was previously only registered on wheat, can help increase yield by reducing plant height an improving straw strength. Regarding the Keep It Clean program, it’s important for farmers to note that Manipulator will carry a ‘no recommendations/ green’ classification for feed and silage barley, but a ‘be informed/ amber’ classification for malt barley. Belchim Canada recommends that farmers who are growing malt barley under contract should discuss the use of Manipulator on barley with their grain buyer. Farmers who are growing barley without a contract, but intend to sell it as malt, are also encouraged to discuss use of Manipulator with potential buyers. For more information regarding Manipulator and barley market access, see the Keep it Clean website at: https://keepingitclean.ca/cereals.
Staging and application rates
Manipulator (active ingredient: clormequat chloride) should be applied prior to the stem elongation stage. Application of a PGR at this stage will signal the plant to begin redirecting resources from stem elongation to other processes, allowing for reduced height and potentially thicker stems and roots. Label directions for Manipulator on barley outline two application strategies:
- A single application between growth stages (GS) 30-39 at a rate of 0.9 L/ac. GS 30 is the beginning of stem elongation. To correctly stage your crop, fold back the leaf sheaths and count the ‘bumps’ caused by each node. By GS 33, all three nodes will be detectable, and by GS 39, the flag leaf will be completely visible. This is similar to the recommendations for a single application on wheat, where the optimal window is between GS 30-39 at a rate of 0.7 L/ac.
- A split application with the first pass between GS 12-32 and a second between GS 32-39, at a rate of 0.45 L/ac. GS 12 represents the two-leaf stage. The second leaf is considered completely emerged when its leaf collar is completely emerged from the sheath of the first leaf. The window for the first application is open until GS 32, when two nodes can be felt on the main stem. The second pass can be made between GS 32, and GS 39, when the flag leaf is completely visible and unrolled. Split application recommendations for wheat outline a first pass at GS 22-23 at 0.3 L/ac and a second pass at GS 37-39 at 0.4 L/ac.
Label directions also indicate that a total of 0.9L/ac should not be exceeded in a single year, and that a full rate of Manipulator should NOT be applied if your crop is stressed from water-logging, drought, or nutrient deficiency. For full label directions, see the 2020 Guide to Field Crop Protection: https://www.gov.mb.ca/agriculture/crops/guides-and-publications/
Effect of PGRs on yield and other agronomic characteristics
Research on agronomic practices to maximize feed barley yield and quality found that application of Manipulator increased both grain yield and starch. The research project, led by Laurel Thompson of Lakeland College, found that starch was increased by an average of less than 1%, while yield was increased by an average of 2.2%. The yield increase was attributed to higher test weight at lower plant densities (22 plants ft-2) but was attributed to longer spike length at higher plant densities (32 plants ft-2). It was also observed that the decrease (1.3%) in plant height from the PGR application did not reduce lodging, even under different plant densities. However, a significant yield increase of 9.3% was observed when a PGR application was combined with post-emergence nitrogen fertilizer and a dual fungicide application. The study suggests that genetic resistance to lodging is the most effective method for Canadian barley producers. Other research from around the world has reported both increases and decreases in grain yield from PGR use, indicating that performance is dependent on many factors including crop type, variety and the environment.
Similar results were discovered by Dr. Breanne Tidemann of AAFC-Lacombe, Alberta. The study looked at agronomic traits, yield and quality effects of a various PGRs on malting barley at sites across Western Canada. In some cases, a PGR application did decrease plant height and lodging, but results were inconsistent and not significant. In general, Tidemann indicated that the inconsistent results of Manipulator suggest that the product is not suited for use on malting barley.
Information for this article was sourced from:
- Belchim Canada Manipulator Brochure: https://www.belchimcanada.com/Brochure/59/E/2.pdf
- Tidemann et al. 2020. Effects of plant growth regulator application on the malting quality of barley. J. Sci. of Food and Agric. 100: 2082-2089. http://www.barleycanada.com/wp-content/uploads/2018/02/P26-Tidemann.pdf
- Perrott et al. 2018. Advanced agronomic practices to maximize feed barley yield, quality and standability in Alberta, Canada. I. Responses to plant density, a plant growth regulator and foliar fungicides. Agronomy Journal 110(4): 1447-1457.
- https://doi-org.uml.idm.oclc.org/10.2134/agronj2017.12.0683
- Thompson et al. 2018. Effect of cultivar and agronomic management on feed barley production in Alberta environments. Can. J. Plant Sci. 98(6): 1304-1320. https://www-nrcresearchpress-com.uml.idm.oclc.org/doi/pdf/10.1139/cjps-2018-0042
