So we had a Frost on our Soybean, Now what?

The first step in accessing frost damage is asking how cold it was last night. A light frost of -1°C for short durations may clip off a few off the top leaves with no effect on yield. The concern begins when a killing frost at least -2°C occurs for an extended period of time. In this situation you will see frozen leaves and pods throughout the canopy.  This may cause quality issues and yield reduction if the crop has not reached full maturity.

See the latest MB Ag Weather latest frost map:

What growth stage are your beans at, see as a reference.

A killing frost at the R8 growth stage will see no yield or quality loss. The R8 stage is when the leaves have dropped off, all pods are brown, and seeds rattle within the pods when plants are shaken.

If however your beans are at the R7 growth stage, (which means one pod on the plant has reached its mature color), research has shown yield loss can range from 5-10 % dependent upon the severity of the frost. Quality issues in the way of green seed may also occur.

Finally, if your beans are at the R6 growth stage-(this is where pods containing a green seed that fills the pod cavity at one of the four uppermost nodes on main stem), yield losses can range from 20-30 %.  You will also have green seed issues which can also lead to marketing concerns.

There are a few areas in Manitoba where the beans are at the end of this R6 growth stage.  Most of the beans in Manitoba are at the R7-R8 growth stage. A light frost should not affect yield and quality for these beans. If beans were at the R6 growth stage and a hard frost occurred yield and quality losses would be noticeable.


Picture: Light frost damage on soybeans near Hamiota, 2016.

Photo from L.Grenkow, Manitoba Pulse Soybean Growers

Submitted by: Dennis Lange, Industry Development Specialist-Pulses, Manitoba Agriculture


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Spring Frost or Late Snow and Emerged Canola – Time to Re-Seed?

Temperature is the instigator for causing frost, but damage inflicted and need to re-seed canola is highly influenced on these other factors:

  1. Duration
    • Short but LIGHT frost = < 2 hours,  may not cause much damage if frost is light (above -1 to -2°C), crop type and staging is tolerant, conditions wet and crop has become acclimatized.
    • Short and HARD frost = < 2 hours, but hard frost (lower than -2°C), crops like canola are more sensitive to longer frost vs. cereals, damage can be variable in field and across area.
    • Long frost = > 2 hours, whether light or hard the longer the negative temperatures the more time for damage to happen.  Tolerance by crop type varies.
  2. Other Environmental Conditions
    • Cloudy and wet – prior to a frost, cool temperatures slow plant growth and ‘hardens’ plants off, which will help them tolerate a frost.  Also wet soil helps buffer the cold air effects on the plants, as wet soils change temperature slower than dry soils.
    • Sunny and dry – The combination of a  dramatic drop in air temperatures when plants are actively growing then a brilliant sunny day after the frost event is where we have seen the most damage.  Scouting after the frost (24 and 48 hours) is very important though to assess extent and percentage of field injury.
    • Field trash cover – increased trash in fields was seen to increase frost damage on very susceptible crops in the 2009 June and May 30, 2015 frost
  3. Crop Type
    • Spring Cereals – more tolerant than other crops types, can tolerant to temperatures as low as -6°C as growing point below ground until the 5 leaf stage.
    • Winter Wheat – can withstand very low temperatures for a short period of time (-11°C for less than 2 hours) up until the tillering stage.
    • Corn – smaller then V5, will recover from light frost as growing point below ground. Leaves probably will be killed, but plants will recover if the growing point ok.
    • Oilseeds – environmental conditions impact frost severity on susceptible canola and flax cotyledons. Resiliency increases at the 3-4 leaf stage (canola) or 2nd whorl (flax).  Sunflowers are fairly tolerant  up to the V4 stage.
    • Pulses – peas are most tolerant, then soybean, edibles bean are very susceptible even before emergence.   Field pea crops are rarely lost to frost. Soybean are more sensitive, but the smaller the soybean plant the more tolerant they are  – from emergence to cotyledon can withstand short light frosts.

Scouting After a Frost (or Snow event)

Scouting should start 24 – 48 hours after the frost and continue for the 5 days following the frost event.  Look for leaves wilting, looking “water-soaked” or see “frost banding”.  Watch for new growth in the plant.  You do not want to see plants wilted and not perking back up or pinching off on the stem near the growing point (canola, flax, soybeans).  Also assess the area affected by frost, small areas or a few plants damaged are ok, as other plants emerged (or just emerging) will fill in those spaces.  Large dead areas may need to be re-seeded.

If in doubt of what look for, call your local agronomists, local FPE Specialist with Manitoba Agriculture or the Crop Industry Branch.

For more specific details on what actually occurs to plants with a frost and crop specific details and symptoms to look for (and how long after a frost to do assessment) see Manitoba Agriculture’s Spring Frost Damage Bulletin.

NEW RE-SEED Calculator developed by Manitoba Agriculture using historic data from MASC is another tool to help determine if re-seeding is finanacially the right decision, depending on plant stands and time of year see calculator at:

Submitted by Anastasia Kubinec, Manitoba Agriculture, Oilseeds Crop Specialist

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Cereal Crops Recovering from Frost Injury

The May 30th frost impacted spring cereal crops across Manitoba. Fortunately, majority of spring wheat, oats and barley were at the tillering stages of development where the growing point is still below ground and therefore protected from the cool air temperatures (the growing point moves above ground at jointing or stem elongation).

However, this doesn’t mean cereal crops escaped without some symptoms of injury.  In MAFRD’s June 3 webinar (available on YouTube at, I covered some of the basics of frost injury symptoms in cereal crops and what to look for in terms of recovery. (And for those interested in canola and flax, my colleague Anastasia Kubinec of MAFRD covered some excellent material for those crop types in the same webinar).

For cereals, you want to look for new leaf growth (normal green color) from the growing point that should follow within 2 to 3 days after the frost event. It can go upwards of 5 days if growing conditions are cool.  Below is a great photo by Lionel Kaskiw with MAFRD which shows barley impacted by frost recovering.  You’ll also notice the water-soaked appearance of some of the older leaves, a classic symptom of frost injury.

Frost Damaged Barley

Frost-Damaged Barley Recovering; Note New Leaf Growth Emerging from the Growing Point – Photo by Lionel Kaskiw, MAFRD (2015)

Fortunately, the loss of leaf tissue at this early stage should have little impact on yield.  But be cautious when applying herbicides in the coming days.  Generally, you want to wait for at least 48 hours after the frost event, as well as seeing the crop resuming growth.  However, please check with your local chemical representative in terms of when it should be safe to apply herbicides after a frost event as it can be product-specific.

More additional information on frost damage, refer to MAFRD’s Spring Frost Damage Bulletin.

Submitted by:  Pam de Rocquigny, Provincial Cereal Crops Specialist, MAFRD


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Frost or Color Banding in Cereals

In Manitoba, cold temperatures during the day and freezing temperatures overnight have been one of the big stories the past week. Cereal crop types are more tolerant of freezing temperatures than other crops types; they can tolerant to temperatures as low as -6°C as their growing point below ground until the 5 leaf stage. However, symptoms of the cold temperatures has resulted in frost banding, or also called color or temperature banding, in cereal crops.

Often the bands appear in similar position on each seedling, so if you view the crop from a low angle, all the bands will line up. Depending on weather conditions, single and multiple bands can happen.

Figure 1. Colour banding in winter wheat in the Estevan area at the end of April 2013.
Color Banding

Photo was taken May 1, 2013. Environmental records for Estevan indicate daily highs from 10-20 °C and lows less than 4 °C. Photo by Jeremy Carlson.

When do we see banding? Color or frost banding occurs on young cereal crop seedlings when temperatures at the soil surface fluctuate widely. Newly emerged plants will exhibit alternate color bands of pale green/yellow and green leaf tissue that correlates with high and low temperatures.

What creates it? Plant growth that occurs in the dark of night is not green but actually white, meaning parts of a leaf that emerges overnight remains white before dawn. When exposed to sunlight, the precursors to chlorophyll will start changing to chlorophyll  (which is the pigment that makes plant leaves green), and the new growth turns from white to green.

When morning temperatures are cold in combination with sunny conditions, destruction of those precursors to chlorophyll can happen, resulting in less formation of chlorophyll.  The end result is the plant tissue turns pale green or yellow. The intensity of banding is determined by the brightness of the early morning sunlight and the temperature. In severe cases, red plant pigments are formed that create brighter-colored bands on the seedlings.  Banding is also more common in deeply seeded crops.

Will there be an impact to yield? Fortunately, affected seedlings usually grow normally with the banding with no effect on yield potential. In more severe cases, the bands may become necrotic and impact nutrient and water flow to the tip of the leaf.

Submitted by:  Pam de Rocquigny, Provincial Cereal Crops Specialist, MAFRD

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Early September 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.  See attached bulletin for more details

2014 Sept Frost and Sunflowers

Visit for more updates on all sunflower issues

Visit MAFRD for more frost information for other crop types

submitted by Anastasia Kubinec, MAFRD Oilseed Crop Specialist

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The Dreaded “F” Word – FROST

Given its sporadic nature, long-range forecasting of frost is nearly impossible. Rather, the climate record of an area is used to determine probable dates of frost based on long-term temperature records. While this will not provide an actual frost date in a particular year, it will present the likelihood that frost may occur on a certain date.

The “Date of First Fall Frost” maps at 50%, 25%, and 10% risk show the likelihood that frost will occur on or before the dates shown within the maps. A frost would be expected to occur 1 in 2 years at the 50% risk date, 1 in 4 years at the 25% risk date, and 1 in 10 years at the 10% risk date.

The extent of frost damage to a crop will depend on several factors. The crop type, stage, and hardening of the crop, the soil type and soil moisture, the actual air temperature, the duration of freezing, and the rapidity with which freezing takes place are all important. A drop in air temperature of short duration will cause less damage than a prolonged period at the same low temperature. When the air temperature drops to 0°C, cereal and other crops may not sustain damage. Rather, damage or total loss is more common when minimum temperatures drop below -2°C, often referred to as a killing frost.

For more information on Manitoba’s Agricultural Climate, please visit our website at

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

Information from the article “Risk of Fall Frost” by Andy Nadler, 2010


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Sunflower Staging and Guessing Maturity

SF G&D chart

Prepared by Anastasia Kubinec, MAFRD Oilseed Crop Specialist

Sunflower planting was spread out in 2014, which means flowering and dry-down will be as well. The chart below gives and indication to the amount of time it will take the crop to reach R8 to R9. This is a guide only. Sunflower development and dry down is based on temperature. If August is all above 25C during the day and doesn’t go below 10C at night, the sunflower crop will develop much faster than this!

From August 5th to 31st, regardless of location, there is typically 275-320 Sunflower GDD accumulated in Manitoba. To get from R5.1 to R9 the crop needs 393 GDD.

Sunflower Stage Sunflower GDD (Celcius)
VE 97
V1 117
V12 333
R1 569
R2 647
R3 726
R4 805
R5.1 883
R5.5 962
R6 1040
R7 1119
R8 1197
R9 1276


*Sunflower GDD= (Tmax+Tmin)/2 – 6.7C

   Example            = ((25+10)/2)-6.7=10.8

For more information, contact NSAC agronomist at (204)750-2555 or MAFRD Oilseed Crop Specialist at (204) 750-2717



Standardized Growth Stages described by Schneiter and Miller. 1981. Description of Sunflower Growth Stages. Crop Science 11: 635-638

Graph Developed by MAFRD Crops Knowledge Centre

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Are Herbicides to Control Dandelions Still Effective After a Fall Frost?

Fall is a great time to work on controlling perennials such as Canada thistle and dandelions. As temperatures get cooler, the nutrients start moving down into the roots and if a herbicide can be taken up and translocated with those nutrients, it can equal better control.

A frost event though, can kill some weeds or can damage leaf tissue which will reduce herbicide uptake and therefore reduce the level of weed control. Within the next few days after the frost, you need to assess the target weeds in the areas that you want to obtain control – are the weeds still growing?  How much leaf tissue has been damaged?

If the plant leaves are still shiny green with minimal leaf tissue damage (i.e. not blackened/brown or brittle) there still may be the window to control the perennial, biennial and winter annual weeds with glyphosate.  If you do spray – spray in the afternoon when temperatures are warm and sunny, this will help with herbicide uptake.   Use rates appropriate to the stage and time of year – fall applications of glyphosate are recommended at a higher rate than when controlling pre-harvest.

One last thing – look at the forecast for the next week following the application.  If the temperatures look like they are going to continually be below freezing each night, it may be too late to make the application to get the economic control you are looking for.

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Should I Still Desiccate My Sunflowers or Has the Frost Done it For Me?


A killing frost in sunflowers is considered to be –4C to –5C for 6 or more hours.

Although we have had a frost, we have not experienced a killing frost yet in Manitoba.  So, the current cold nights have not been cold enough to substitute for a desiccation.

A desiccant may still be considered, if no other frost is is the forecast, but as we have now gotten cooler, plant metabolism has slowed down. The plants are not metabolizing the harvest aid desiccant products as quickly and dry-down will take longer.

To optimize the benefits of applying a desiccant, it is necessary to look at the weather forecast for the next week.

How cold will it get? If a frost below –4C is expected, a desiccant might not be required

How warm will it get? Desiccants perform much better if applied in temperatures >20 C

Applications to healthy green plants will provide optimum results. Since we have had a lack of morning dew lately, it is extremely important of maintain water volumes to get proper coverage.

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