Effect of Spring Frost on Emerging Crops

Submitted by Anastasia Kubinec, Manitoba Agriculture, Oilseeds Crop Specialist

Originally posted May 8th and 30th, 2015…..re-post May 13, 2016.

Don’t assume because there is frost (or snow) on the ground, that your emerging crop in dead!

With the drop in temperatures in the past couple of days, there are a few things to keep in mind if the mercury dips below 0°C. The temperature is the instigator for causing frost, but whether it is -0.1°C or -4°C the damage inflicted is highly influenced on these other factors:

  1. Duration
    • Short 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 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 frost is 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 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

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.


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Are your Soybean leaves looking scorched?

Submitted by John Heard, MAFRD Crop Nutrition Specialist

During seed fill,  potassium deficiency symptoms is most commonly observed in soybeans.  Potassium is a mobile nutrient, meaning that as deficiency occurs, usually lower leaves are scavenged of potassium in order to support new growth.  This early season deficiency appears as yellowing and later browning of lower leaf margins (Figure 1).

 Soybeans remove alot of potassium/acre in the seed – about 1.4 lbs K2O/bu.  As seeds fill, some of the potassium that is stored in the plant leaves is mobilized for movement to seeds..  Then one may observe deficiency symptoms appearing on upper leaves (Figures 2 and 3).

 The likely areas with potassium deficiency are lighter textured or sandy soils, peat soils or cropping systems where past potassium removals have been high without replenishment.  These symptoms can be verified with tissue testing but should ultimately trigger soil sampling to determine the rate of potassium to be applied.

K deficny symptoms in soybean

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Manitoba Insect & Disease Update – Week of July 7th to 11th

A Manitoba Insect and Disease Update for the week of July 7-11, 2014 has been posted at: http://www.gov.mb.ca/agriculture/crops/seasonal-reports/insect-report-archive/insect-report-2014-07-09.html

A few quick highlights from the update:

  • Leaf rust spots have been observed in fall rye as well as a few spots resembling Septoria leaf spot.

Leaf rust spots on fall rye, 2014. Photo courtesy: Vikram Bisht, MAFRD

  • Blackleg spots can be found on canola foliage.
  • Remember to collect samples or notify someone from MAFRD if you are noticing cereal leaf beetle in cereal crops. Levels are quite low in Manitoba, however we are doing a  release of a parasitoid that is very effective at keeping cereal leaf beetle at low levels. The samples of larvae will be sent to AAFC in Lethbridge, where they will be examined for parasitoids. Areas of Manitoba where larvae are present but not already containing parasitoids will be given priority for parasitoid releases.

Larvae of cereal leaf beetle.

Submitted by: John Gavloski, Entomologist & Vikram Bisht, Pathologist, MAFRD

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Why Are My Soybeans Yellowing?

With cooler and wet conditions, iron chlorosis has been showing up in a number of soybeans fields around Manitoba.

IDC in soybean. photo: Dennis Lange, MAFRD FPA

IDC in soybean. photo: Dennis Lange, MAFRD FPA

IDC is the plants inability to uptake iron due to high soil pH, high carbonate levels and high salt levels. Initially the soybean leafs will turn yellow and as symptoms progress growers may note interveinal yellowing. The dark greens veins of the soybean leaf is a tell tale sign of IDC. If symptoms are severe you will see necrotic tissues on the leaves and short stunted plants. If growers do see this occurring in fields the best thing to do is to take the long way home from town for about a week until you get a bit of warmer weather so the beans can grow out of this condition. For future years growers can use the IDC ratings listed in the soybean table of seed Manitoba to help choose a variety for a particular field that is rated higher for tolerance to IDC.

IDC in soybean field. photo: Dennis Lange, MAFRD FPA

IDC in soybean field. photo: Dennis Lange, MAFRD FPA


Submitted by Dennis Lange, MAFRD FPA (Altona)


More information on soybean production can be found at http://www.gov.mb.ca/agriculture/crops/production/soybeans.html

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When is the Best Stage to Roll Soybeans After They Have Emerged?

Submitted by Dennis Lange, MAFRD Farm Production Advisor (Altona).  Updated from Manitoba Cooperator article by Allan Dawson, published on June 27, 2013 “Trifoliate stage best for rolling soybeans after emergence”

Don’t roll soybeans until they reach the first trifoliate stage, or you risk breaking too many young plants.

  • You don’t want any beans at the hook stage
  • Only roll if you have some stones or dirt that will cause you some harvest issues
  • Wait until later in the day when it’s warmer and plants are more plastic and should have less breakage (check to see if plants are breaking) 

Why Roll Your Soybean Field?

Rolling pushes down stones and levels the field allowing the combine cutter bar to be set lower and pick-up low-handing pods.  It can make soybean harvesting faster, more efficient and will reduce the risk of stones damaging the combine.

Soybean plant at firth trifoliate. Picture by Dennis Lange, MAFRD

Soybean plant at first trifoliate. photo: Dennis Lange, MAFRD

These emerging soybeans are at the hook stage. Rolling plants at this stage will cause a lot of plant damage. photo: Dennis Lange, MAFRD


This soybean plant is at the unifoliate stage with two true leaves and the cotyledons below. photo: Dennis Lange, MAFRD


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Seeding Date Relationship to Crop Yield

One of our most used extension messages is seed early!

In a year that is later, this may cause some concern that seeding into the second half of May is not going to have good crop yields. Typically seeding earlier does normally translate into higher yields, but good yield potential remains when seeding throughout the month of May, provided you don’t compromise the seeding operation.

Things Other than Seeding Date That Influence Yield:

  • Using clean seed with high %germination
  • Applying the appropriate fertilizer nutrients and rates to support yield goals
  • Seeding for a good plant stand – taking in account TKW, %germination and seed mortality!
  • Seeding into a firm seedbed
  • Seeding into soil warm enough to result in quick germination and emergence
  • Timely weed control
  • Timely fungicide application if needed
  • Appropriate harvest operation timing

2005-13 Seeding Date x Yield

Table 1: Crop Yield Response to Seeding Date (2005-2013)

Source: MASC – Harvested Acreage Report (2005-2013)

For more information see MAFRD website post “Crop Choice Considerations in a Delayed Year”  http://www.gov.mb.ca/agriculture/crops/production/crop-choice-in-delayed-year.html


 Contributed byAnastasia Kubinec, MAFRD Oilseed Crop Specialist



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What are minimum germination temperatures?

Soil temperature is a useful gauge for timing when crops are seeded.  Table 1 shows the minimum germination temperatures for various crops.  These values should be regarded as approximate since germination depends on several factors.  If the soil is too cool, germination can be delayed which can result in uneven or inadequate seedling emergence.

How do I measure soil temperature?

Determine how deep you will be seeding. Then place your soil thermometer at that targetted depth. Take two measurements throughout the day: one in the morning (8am) and one in the early evening (8pm) . Average the two readings to determine the average soil temperature.

MAFRD recommends that you take readings for two to three days to establish a multiple day average, and reminds you to measure temperature in a number of locations in the field, to account for field variability.  Still not sure, see soil temperature data for various locations across Manitoba is available from MAFRI’s Ag-Weather Program:  http://tgs.gov.mb.ca/climate/SoilTemp.aspx.  This can be used as a guideline for an area, but in-field measurements are going to tell you what is actually going on in your field!

Table 1: Minimum Germination Temperatures for Various Crops

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

Sources: North Dakota StateUniversity Extension Service, Alberta Agriculture & Rural Development and Canola Council of Canada

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Updated Treated Seed Best Management Practices

The Updated Treated Seed Best Management Practices document is now posted to the Health Canada website:  http://www.hc-sc.gc.ca/cps-spc/pubs/pest/_fact-fiche/pollinator-protection-pollinisateurs/treated_seed-semences_traitees-eng.php

The PDF of the updated document is also available:  Pollinator Protection and Responsible Use of Insecticide Treated Seed_January 8, 2014 (Health Canada)


Best Management Practices

Insect pollinators are vital to agricultural production and the environment. Many farmers, including those who grow corn and soybeans, use insecticide treated seed to protect their crop from insect pests. Some insecticides, such as neonicotinoids, are toxic to pollinators. Planting of treated seed can spread dust that contains insecticide into the air, placing pollinators at significant risk of exposure to toxic insecticides. Factors that impact the risk of exposure include the use of treated seed, type of planting equipment, planting conditions, flowering resources and bee yard locations.

The following Best Management Practices (BMPs) are provided to reduce the risk to bees and other insect pollinators from exposure to dust from treated seed. The BMPs provide a toolbox of options that should be used in combination wherever possible.

  1. Read and adhere to the pesticide label and seed tag directions
  2. Practice Integrated Pest Management when choosing seed treatments
  3. Develop and maintain shared communication with beekeepers to help protect honeybees
  4. Recognize pollinator habitat and take special care to reduce dust exposure
  5. Avoid generating dust when handling and loading treated seed
  6. Managing planting equipment to decrease dust drift
  7. Use appropriate seed flow lubricant
  8. Ensure proper clean-up and disposal

Submitted by:  Pam de Rocquigny, MAFRD Cereal Crops Specialist & John Gavloski, MAFRD Extension Entomologist

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Guidelines for Responsible Use of Neonicotinoid Seed Treatments

Prepared by Dr. John Gavloski, Field Crop Entomologist, MAFRD Crops Knowledge Centre

 Potential Risks (costs):     

  1. Increase in selection pressure to develop resistant insect populations if technology is overused.
  2. Potential increase in secondary pest populations
  3. Potential non-target impacts of the insecticide
  4. Increased cost to producer

 Potential Benefits:

  1. Reduced injury to crop from economic populations of insects that may be managed by insecticide
  2. Potential increase in early-season vigour of the crop under some growing conditions.        

When all components of the equation are considered, and the science to support all the components, a neonicotinoid-based seed treatment is most likely to be beneficial when there is a high risk of flea beetles (in canola), wireworms, or seedcorn maggots causing economic damage to the crop. Using neonicotinoids as “insurance” if the risk of damage by these insects is low, is not likely to be the most economical choice in most years.  

Regarding the potential increase of secondary pests, this is probably of greatest concern in corn and soybeans in drier years, where neonicotinoid seed treatments can potentially increase the risk of spider mites (Henry and Szczepaniec. 2013. Ent. Soc. America Ann. Mtg).

Regarding potential vigour-effects of neonicotinoid seed treatments, there are studies that do show some increased early season-vigour, regardless of whether insects are present, and other studies where this vigour effect did not occur. So a potential increase in crop vigour may occur, but may be dependent on growing conditions.   Using a neonicotinoid-based seed treatment for the primary purpose of increasing seedling vigour may not be the best use of the technology either economically or sustainably. In a risk/benefit analysis,  the 4 potential costs mentioned above need to be weighed against a potential increase in early-season vigour when deciding on a seed treatment. The other factor, and possibly the most important in the equation, is what is the risk of insects that the seed treatment may control (in Manitoba this would be flea beetles (on canola) or wireworms or seedcorn maggots).

In Canola: There are currently no seed-treatment alternatives to neonicotinoid insecticides (Lumiderm is currently applied with a neonicotinoid seed treatment). Flea beetles are a chronic and potentially serious pest of canola. Thus neonicotinoid-based seed treatments will likely remain an important management tool until alternative seed-treatments are available.

In soybeans and corn: Reduction in damage by wireworms and seedcorn maggots may occur if populations are high. Reduction in risk from soybean aphids would also be a consideration in some parts of North America, but not likely in Manitoba because the residual effect capable of providing control reaches levels that would be ineffective at killing aphids between 35 and 49 days after planting (McCormack and Ragsdale, 2006: Crop Management; Johnson et al., 2008. J. Econ Entomol. 101: 801-809; Tomizawa and Casida, 2003. Ann. Rev. Entomol. 48: 339-364).  So decisions on seed treatments in these crops in Manitoba, as well as other pulse crops, would most appropriately be based on the risk of wireworms or seedcorn maggot.

In Small grain cereals:   Decisions on whether a neonicotinoid-based seed treatment should be considered in these crops in Manitoba would most appropriately be based on the risk of wireworms.

In Potatoes: Wireworms can be a big concern and some control of other insects such as Colorado potato beetles is possible. Neonicotinoids will likely continue to be used quite extensively until other seed treatment or in-furrow options are available. A cautionary note, however, that Colorado potato beetle resistance to neonicotinoids has been documented in some parts of North America (Szendrei et al. 2012. Pest management Science. 68: 941-94).

Through a responsible use program and careful attention to how seeds are applied, many of the risks of neonicotinoid insecticides can be minimized. What commodity groups, and possibly even the companies that market neonicotinoid seed treatments, need to be concerned with is the overuse of the products when risk of potential threats the seed-treatments can control are low, and that all efforts are made to reduce the drift of dust from seed-treatments when planting corn and soybeans.

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Soybean Harvest Losses Based on Cutting Height

Prepared by : John Heard, MAFRD Field Crop Nutrition Specialist

There is always incentive to minimize harvest losses.  Here is a graph of measured losses due to improper cutting height in a low podding variety in 2013: Soybean Yield Loss Due to Cutting Height

Make sure you visit your farmer clients as they harvest to do some harvest loss measures.  Determine the average loss per square foot and divide the number of seeds by 4 to estimate bu/ac loss.  Cutter bars cutting stems at 2” will minimize stubble harvest loss.  If the combine operator will not slow down to 3 mph to maintain a low cutting height, then your farmer cannot afford to let them leave so much crop in the field.


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