Quick Tips – Effective Post-Emergent Weed Control in Conventional Soybeans

If you have only grown glyphosate tolerant soybeans in the past, the move to conventional soybeans can offer up new challenges in regards to weed control. Good weed control is critical for maximizing yield.  Here are a few quick tips:

    • Remember!! You can’t apply post-emergent glyphosate – Unlike glyphosate-tolerant soybeans, conventional soybeans are not a clean-up crop for weedy fields. They are a crop that needs to be planted in fields that have already been cleaned up.
    • Get in touch with your weed spectrum – If you have not done so already, determine what weeds are present or likely to be present in your conventional soybean fields. Are the herbicides you intend to use going to control the weed spectrum you have identified? A mismatch between weed spectrum and herbicides used is a frequent cause of weed control problems in conventional soybean fields.
    • Did you take advantage of pre-emergent weed control opportunities? If so, how is that working? – The advent of pre-emergent soil applied residual products has been a benefit to weed control in conventional soybeans. If this is a tool you decide to use, it is important to assess its effectiveness before you do post-emergent applications to ensure that weeds you are assuming have been dealt with have been controlled.
    • Amp up the Aggression!! Early and thorough weed control is key – Important regardless of the type of soybean you are growing. Research has demonstrated the critical weed free period for soybeans is emergence to the third trifoliate, where the removal of weeds provides the greatest protection of yield potential. Be timely with control and selective with products that may provide some residual control for an extended weed free period.
  • Know your crop growth stage, know your weed growth stageKnowing your crop and weed growth stages as you time herbicide applications is very important in conventional soybean production. Most of the herbicides available have tighter application windows than glyphosate


  • Overgrown weeds are less susceptible to herbicides – this can lead to growers dishing out more money on higher cost options that might not work due to size of plants. Please take note that some herbicides can cause crop damage if they are used at the wrong growth stage. In this competitive fight for yield, you don’t want to set back your crop.



  • Assess the effectiveness of herbicide applications and adjust your plan – Fields should be scouted after each herbicide application to assess effectiveness. If weeds have shown up that the previous herbicide would not have controlled, you might have to change products for your next application or add extra herbicide passé. Were the weeds that you expected to be controlled, actually controlled? Don’t assume that you have dealt with target weeds until you see the evidence. These post-spraying inspections are key opportunities to detect the development of herbicide resistant weeds before they get out of hand.
  • Weed control in conventional soybeans is going to cost more – Seed may be cheaper, but the cost of an effective weed control program in conventional soybeans is almost always more expensive than in glyphosate-tolerant production. But remember, poor weed control remains the #1 threat to maximizing yield and profit in conventional soybeans. Weed control is a key point of investment in this crop and there are no shortcuts if the weed control situation demands action.
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Post-Emergent Weed Control in Xtend Soybeans – Slow Down and Be Careful

The future of side by side soybean fields using different herbicides is here with Xtend soybeans commercially available in 2017.  Having more herbicide tools to combat the herbicide resistant weeds is important, but careful use is critical, to prevent crop damage and stay friends with our neighbors. Here are a few things to consider:

  • Non Xtend soybeans (and other crops) are easily damaged by dicamba – dicamba on sensitive crops always causes crop damage with very dramatic looking symptoms. As glyphosate -tolerant soybeans made up the majority of acres in the past and usually only sprayed with glyphosate, drift went unnoticed. The addition of Xtend soybeans to the cropping mix will be a reawakening to anyone who has gotten careless.
  • Should your pre-emergent application have been the one that included dicamba? – preferred timing for dicamba containing herbicides for use on Xtend soybeans is pre-emergent. Research has demonstrated the critical weed-free period in soybeans is emergence to the third trifoliate, early weed removal provides the greatest yield potential. Additionally, dicamba provides residual control for some weed species during that critical period. Another important point is, chances of application mistakes like drift on sensitive crops are greatly reduced during pre-emergent applications.
  • Only use herbicides specifically designed for the Xtend system – do not tank mix dicamba and glyphosate that you might have on hand in an attempt to make “homemade” herbicide for Xtend soybeans. The herbicide manufactured is designed specifically for use in Xtend soybeans, with reduced levels of volatilization, to prevent herbicide drift. Keep in mind the reports on the U.S. experience in 2016.  Homemade concoctions are a very bad idea, plain and simple.
  • The label is your friend…follow it! – the labels contain important information that will help minimize chances of accidental herbicide drift onto susceptible crops. Key points include:
    • Use nozzles delivering extremely coarse to ultra coarse spray droplets (volume median diameter of 450 microns or more) as defined by ASABE standard S572.1 and as shown in the nozzle manufacturer’s catalog.
    • Do not apply:
      • when risk of severe temperature fall in the night;
      • under high humidity, temperatures above 30oC, or fog conditions, to prevent drift to sensitive crops;
      • when wind is blowing toward a nearby sensitive crop;
      • when winds are below 3 km/h or above 15 km/h.

Source: Guide to Field Crop Protection 2017 p. 163

  • All soybeans look alike – know what field you are in – there is no way to visually discern between the different types of soybeans. When in doubt, make sure that the applicator is in the right field. Herbicides specifically designed for the Xtend system applied to Roundup Ready or conventional soybeans will cause significant crop damage. Additionally, knowing the types of soybeans in the adjacent fields is important to indicate increased risk for off target crop damage. Remember, dry beans look like soybeans from far enough away….never make assumptions.
  • Sprayer cleanout requires careful attention – If producers are growing two or more types of soybeans on their farms, careful consideration has to be given to sprayer cleanout as they move between soybean fields. Even a small amount of dicamba will serve as a contaminant in the next spray load being applied, causing significant damage. Especially if you have only grown Roundup Ready soybeans in the past, recognize that the situation has gotten more complicated.
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When to Roll Your Soybeans

Most growers will roll their beans shortly after seeding in order to prevent stones from entering the combine at harvest time and to make harvesting easier and quicker. On dry springs when soil conditions could lead to soil drifting a grower can wait and roll there beans after they are up and are at the first trifoliate stage..

When rolling after emergence

  1. Do not roll at the Hook Stage- This is when beans are first emerging.
  2. Do not roll in the morning wait until air temperature are around 25C before you start to roll to avoid damage to the plants.
  3. Check for damaged plants to ensure plants are not breaking off.
  4. If damage is too sever wait for a warmer day.


The attached video outlines some of the reminders about rolling beans.

Soybean School West: Why Rolling Matters & Timing it Right

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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: http://www.gov.mb.ca/agriculture/weather/pubs/minimum-air-temperature.pdf

What growth stage are your beans at, see http://www.manitobapulse.ca/soybean-staging-guide/ 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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First ask yourself if you need to control the volunteer canola in your crop.  Research by Dr. Rob Gulden and graduate student Paul Gregoire at the University of Manitoba (U of M) showed that volunteer canola had little impact on soybean yield when there are less than:

  • 3 plants/m2 in solid seeded or narrow row soybean, or
  • 1.5 plants/m2 in wide row soybean.

Although economic thresholds (ET) such as these don’t consider seed return, this is generally not a concern for canola given it’s prevalence in our crop rotations.

If your volunteer canola populations exceed the ET, the U of M researchers also assessed the effectiveness of various post-emergent herbicides (Table 1).  Control of volunteer canola by the herbicides listed in table 1 are based on comparisons of treated research plots.  It’s unlikely that any of these options will provide full control of bolting or flowering volunteer canola.

Table 1: Ranking and application timing of volunteer canola herbicides in soybean

Vol Canola Control in Soybeans

*Will not control CLEARFIELD canola volunteers

**Registered in the Red River Valley only

Another consideration: use of these herbicides on larger volunteer canola may only set plants back, resulting in later flowering canola that may cause issues during soybean harvest.

Previous research by Dr. Gulden has shown that one of the best ways to manage volunteer canola is by limiting weed seedbank additions from canola harvest losses. Slower combine speeds while harvesting this year’s canola is a good way to reduce volunteer canola populations in future soybean stands.


Submitted by Dr. Jeanette Gaultier, Weed Specialist, Manitoba Agriculture

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Understanding the 2015 Western Manitoba Soybean Adaptation Trial Table

The Western Manitoba Soybean Adaptation Trial table combines elements of both long term data and single site year data.

You start by using the long term data listed on the left half of the table to assemble a short list of varieties. Information includes Company Maturity Grouping, Variety Name, Yield % Check, Site Years Tested and Relative Days to Maturity +/- of Check. As you go down the table you will see that varieties are listed from earliest maturing near the top to later maturing near the bottom based on Relative Days to Maturity +/- of Check (23-10RY).  The Yield % Check and Site Years Tested should be used together when comparing the varieties.  The Site Years Tested represents the total number of locations a particular variety has been tested and the Yield % Check represents the yields of those varieties based on the number locations tested.

The right half of the table includes the 2015 Yield % of 23-10RY for five individual Western Manitoba sites and can help you refine your variety short list.  To assess real yield differences between any two varieties within a location using this table, start by looking at the LSD% at the bottom of the table. The LSD (Least Significant Difference) is the minimum difference required between any two varieties compared at the same site. For example, the LSD% for the Boissevain is 9% and yield for the check variety (23-10RY) has been set at 100%. Only varieties that yielded 109% or greater would be considered higher yielding than the check and only varieties that yielded 91% or less would be considered lower yielding than the check. Any other varieties are considered to be yielding the same as the check. We are not restricted to only comparisons with the check variety when using this single site year data.  Yield comparisons can be made between any two varieties at the same site using the LSD% for that site.  Caution should used when making variety decisions based on one year’s data. Using the long term data listed on the left half of the table will give you a better feel for how a variety performs over multiple site years.

Submitted by Dennis Lange, FPE Altona and Terry Buss, FPE Beausejour

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Understanding the 2015 Roundup Ready Soybean Variety Evaluation Tables

It’s that time of the year when the MPSG publishes the Soybean Variety Evaluation.  This article will look at how to use the variety evaluation tables effectively when considering yield and maturity. Additional variety characteristics are also listed in these tables. The 2015 Soybean Variety Evaluation can be found at http://www.manitobapulse.ca/variety-data.  Hard copies will be available as part of Seed MB 2016 and as an insert in the December 2015 issue of the Pulse Beat.

Roundup Ready Soybeans – Variety Descriptions Table

The first table to look at is the Roundup Ready Soybeans – Variety Descriptions table. The varieties are divided into Short Season, Mid Season and Long Season Manitoba Variety Zones based on relative days to maturity, with the shortest maturing varieties at the top of the table and the longest maturing varieties at the bottom.  The Relative Days to Maturity +/- of Check, are averaged over the 3 growing seasons but some varieties may only have 1-2 years of testing. Use these parts of the table to select varieties that have similar maturity to where you farm. Your goal in using this table is to assemble a short list of varieties you might consider growing.

The Yield % Check and Site Years Tested should be used together when comparing the varieties. The Site Years Tested represents the total number of locations a particular variety has been tested at. The greater the number of sites years, the more confident you can be that the Yield % Check reported is representative of the variety.  For example, 24-10RY (check variety), has 41 sites years.  Given that there are six to seven soybean variety trial sites per season, 24-10RY has been tested for at least six growing seasons.

Using Relative Days to Maturity +/- of Check and Yield % Check, your goal is to identify varieties, with maturities suitable to your farm that give you the highest yields relative to the check.  Keep an eye open for varieties that provide satisfactory yields but are earlier maturing.  These may represent good opportunities to avoid late season frost.

Yield By Location – Roundup Ready Soybeans Table

Here the sites are listed individually and are grouped into Core Sites, Early Sites, and Late Sites.  All varieties are tested at core sites. At early sites only early to mid season varieties are tested and at the late sites only mid to long season varieties are tested.

To assess real yield differences between any two varieties within a location using this table start by looking at the LSD% at the bottom of the table. The LSD (Least Significant Difference) is the minimum difference required between any two varieties compared at the same site. For example, the LSD% for the Carman Site is 12% and yield for 24-10RY has been set at 100%.  Only varieties that yielded 112% or greater would be higher yielding than the check.  Only varieties that yielded 88% or less would be lower yielding than the check. Any other varieties are considered as yielding the same as the check. We are not restricted to only comparisons with the check variety.  Yield comparisons can be made between any two varieties at the same site using the LSD% for that site.  Caution should used when making variety decisions based on one year’s data.  Using the long term data listed in the Variety Descriptions table will give you a better feel for how a variety performs over multiple site years.

Submitted by Dennis Lange, FPE Altona and Terry Buss, FPE Beausejour

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Confused about Fluency? Read on…

Submitted by Jeanette Gaulthier, MAFRD Pesticide Use Specialist and Holly Derksen, MAFRD Field Crop Pathologist

The PMRA requires the use of Fluency Agent as the seed flow lubricant when planting corn or soybean treated with a neonicotinoid insecticide (a list of products is included in the link below). Fluency Agent produces 65 percent less dust than talc or graphite and may significantly reduce the risk of neonicotinoid exposure to bees and other pollinators.

This requirement only applies to treated corn and soybean seeded using vacuum planters. Although not required, Fluency Agent can be used in all types of planters.

As with anything new, producers using Fluency Agent for the first may have a bit of a learning curve before things run smoothly. Nathan Klassen, Seed Growth Specialist, with Bayer CropScience offers these tips to avoid hiccups:

  1. Give it a mix. Add Fluency Agent to the seed tote or planter box and give it a quick stir with a stick or gloved hand – 30 seconds is more than enough. A thorough mix before the first run of the year with your planter helps lubricate the equipment; a quick mix when refilling the planter during your subsequent fills ensures the product is mixed within the seeds.


  1. When it comes to Fluency Agent, less is more.   A 1/8 cup treats 1x 50 lb bag of seed or a 400 gram container treats 1 seed tote (50 bags). Don’t over apply the product; there is no advantage to adding extra to your seeds before going into the planter.

Fluency Agent is available from your corn and soybean seed dealers as well as select equipment dealerships.

Use of Fluency Agent is just one way to reduce the risk of neonicotinoid exposure to bees. Visit the Manitoba Corn Growers Association website for a full list of Best Management Practices: http://manitobacorn.ca/public-policy/


Pest Management Regulatory Agency Requirement when using Treated Corn/Soybean Seed: www.hc-sc.gc.ca/cps-spc/alt_formats/pdf/pubs/pest/_fact-fiche/pollinator-protection-pollinisateurs/treated_seed-2014-semences_traitees-eng.pdf

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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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