Manitoba Weed Update

Despite rainy and windy conditions, early post-emergent herbicide applications are nearing completion in most crops. Emergence of cool season annual weeds was relatively unaffected by earlier cool, dry conditions while emergence of warm season annual weeds was delayed, resulting in herbicide staging issues for some producers.  Emergence of warm season annuals, like redroot pigweed and barnyard grass, is now well underway due to recent rainfall.

Weed Identification:

Weed identification form: www.gov.mb.ca/agriculture/crops/crop-diagnostic-services/.  Weeds submitted to Manitoba Agriculture for identification in the previous week include:

Black nightshade:

Black nightshade (Solanum nigrum) is a warm season annual problematic in potato, dry bean and soybean production.  What to look for: small seedlings with pointed ovate cotyledons, currently in the cotyledon to early true leaf stage (see picture submitted to MB Ag).

Galinsoga species:

Hairy galinsoga (Galinsoga quadriradiata) and smallflower galinsoga (Galinsoga parviflora) are annual species also referred to as ‘quickweed’ based on their ability to set seed within only weeks after emerging.  What to look for: toothed, opposite leaves and ‘club’ shaped cotyledons (see picture submitted to MB Ag).

Oak-leaved goosefoot:

Of the various goosefoot species coming in for identification, oak-leaved goosefoot (Chenopodium glaucum) has been the most common.  What to look for: goosefoot shaped leaf, often with distinct yellow-green veins.  Stems may be red and green to red.  Typically grows more prostrate than lamb’s-quarters.  Oak-leaved goosefoot does especially well in wet and/or saline areas.

Weed Management Issues:

Manitoba Agriculture staff have begun to receive herbicide drift complaints and are providing advice accordingly. Talking to the applicator should always be the first step in a suspected drift incident.  Herbicides involved in the drift complaints to date include glyphosate, group 2 and group 4 herbicides.

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Why is my Corn Purple?

Many Manitoba corn fields are showing some degree of leaf purpling this spring. Here’s a quick look at why leaves turn purple and what possible causes may be.

 

Leaf purpling is a sign of stress. The leaves are actively producing photosynthates (sugars) but conditions are not allowing normal sugar metabolism or translocation in the plant.  The purple anthocyanin pigment is associated with this sugar buildup in leaf tissue.  The amount of purpling is genetically controlled, so hybrids with more of the purpling genes will appear worse than others, even though all suffer the same stress.

Common stress conditions triggering this purpling are:

  • Warm sunny days but cool nights (4-10oC) – this allows sugar buildup but not metabolism
  • Restricted root growth and development – soil compaction (Figure 1), herbicide injury (such as Edge carryover- Figure 2), standing water.
  • Impaired phosphorus uptake due to insufficient soil phosphorus, lack of phosphorus starter fertilizer (Figure 3) or following non-mycorrhizal crops like canola.
  • Physical injury – recently wind has crimped leaf tips (Figure 4) causing sugars to buildup without being translocated to other growing parts of the plant

Purpling will often dissipate with warmer days and nights and yield loss is slight if any. But severe purpling is a symptom of crop stress, so the astute crop advisor or farmer will exploit it as a visual signal and will investigate the cause so to manage better next year.

 

 

 

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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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Don’t Overlook Group 2 Herbicide Resistance

You’ve probably read about media dubbed ‘superweeds’ like glyphosate-resistant palmer amaranth and giant ragweed. Glyphosate-resistant weeds often earn this distinction because they are viewed as a greater management hardship for producers than weeds resistant to other herbicide mechanisms of actions (MOAs).  And maybe rightly so.  Farmers dealing with glyphosate resistant weeds elsewhere in the world have been reduced to tillage and hand rouging for weed control in some crops.

But, while glyphosate use dominates the Roundup Ready corn, soybean and/or cotton rotation in the US, group 2 herbicides play an (equally?) important role in our more diversified cropping system. For example, group 2 herbicides are used in crops like alfalfa, corn, dry beans, field pea, potato, soybean, sunflower, and in Clearfield and other group 2-tolerant crops.  These herbicides are also a popular choice for group 1-resistant grassy weed control in cereals.

The point of this article isn’t to downplay the importance of glyphosate resistance but to elevate consideration of group 2 resistance. In Manitoba, over 10 weed species are known to have biotypes resistant to group 2 herbicides.  And herbicide-resistant weed surveys led by AAFC indicate that the prevalence of certain species is increasing (Figure 1).

Figure 1: Prevalence of group 2 resistance in Manitoba in 2003 and 2008 as a percent of the weed species population surveyed (Beckie et al).

 

The following practices can help reduce the risk of developing herbicide resistant weeds and/or managing existing resistant weed populations:

  • Diversifying your crop rotation;
  • Using multiple herbicide MOAs effective on target weeds (e.g. herbicide ‘layering’, tank mixing);
  • Practising good basic agronomy (variety selection, seeding rates, etc.);
  • Judicial use of tillage.

If you suspect group 2 resistance in a weed species on your farm, it’s best to verify this by herbicide-resistance testing. Unfortunately there‘s no quick method – seed from the suspect population needs to be allowed to mature and collected.  Samples can be submitted to AgQuest for testing in Manitoba.

In my opinion, knowing if you have group 2 resistance and assessing your risk factors is worth it. Because while glyphosate resistance is grabbing headlines, group 2 resistance may be quietly growing in your fields.

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Blackleg in Canola – to spray or not to spray?

Things to consider:

  1. Crop rotation – the tighter the rotation the higher the risk of blackleg
  2. Historic levels of blackleg in that field – have you experienced yield loss from blackleg?
  3. Weather forecast – infection requires free moisture (light-moderate rainfall, not soil saturation)
  4. Presence of inoculum –can you see leaf lesions on first true leaves? or pseudothecia present on canola stubble?
  5. Yield potential – what is your target yield, return on investment expected?

If you have made the decision to spray, what else do you need to know?

  1. Application timing – apply at the 2 to 4 leaf stage, later applications are not as effective at reducing disease.
  2. Fungicide type – strobilurin fungicides (Group 11) are more effective at reducing disease than triazoles (Group 3). For more information on what products are registered for blackleg management, see the MB Guide to Field Crop Protection http://www.gov.mb.ca/agriculture/crops/guides-and-publications/pubs/crop-protection-guide-disease.pdf.
  3. Yield increase….not guaranteed – while strobilurin fungicides applied at the 2 to 4 leaf stage did significantly reduce the severity of the disease, yield bumps were only observed when a susceptible cultivar was grown.

 

 

 

Reference: Liu, C. 2014. Evaluation of fungicides for management of blackleg disease on canola and QoI-fungicide resistance in Leptosphaeria maculans in Western Canada. Master of Science Thesis. University of Manitoba. 172 pp.

 

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Manitoba Crop Report #5 – June 5, 2017

Hot dry weather dominated the past week, with limited precipitation. Strong winds causing soil drifting in fields with limited ground cover. Seeding is 95% complete, with exception of The Pas region which is delayed from earlier heavy rains. Crops planted are advancing, with herbicide applications starting. Flea beetle feeding has been seen in canola. Haying is starting this week. For more information visit http://www.gov.mb.ca/agriculture/crops/seasonal-reports/crop-report-archive/crop-report-2017-06-05.html

What is Waterpod?

Waterpod is:

  1. an annual weed occasionally found in agricultural fields;
  2. a mobile irrigation system; or
  3. a one person submarine?

 

 

If you chose a), you’d be right. Waterpod (Ellisia nyctelea L.) is an annual broadleaf plant native to Manitoba.  It’s often found in shaded, wooded areas but can also thrive in ditches and agricultural fields.  Our wet soils and cool spring must have provided ideal conditions for waterpod emergence as it’s being found in abundance in fields across the province.

The good news is waterpod isn’t much of agricultural pest.  Although it’s an annual, it emerges and flowers early and usually dies off in June.  It’s also very susceptible to glyphosate and most other burn-off and post-emergent herbicides.

Identifying characteristics:

  • oval cotyledons with a flat top;
  • deeply lobed and hairy leaves;
  • small, white 5-petaled flowers.

 

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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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Why is the 2017 Guide to Crop Protection SO BIG?

If you’ve picked up a copy of the 2017 Guide to Crop Protection, you’ve probably noticed that it’s BIG! (Sadly, more crop protection products are not the reason why).

The extra 100+ pages of the Guide are largely due to the new single column format with larger font (Figure 1). These changes were made to improve the readability of the Guide.

Other changes to the 2017 Guide include:

  • Placement of the Pesticide Index, which you can now find at the back of the book.
  • Information on maximum residue limits (MRLs) on page 6. Crop protection products flagged by the Keeping It Clean initiate also have a statement on the product pages in the Guide.
  • The herbicide site of action table on page 44 now also separates active ingredients and products by their chemical family to assist with herbicide resistance management.

The Guide to Crop Protection can be purchased for $10.00 at Manitoba Agriculture offices. A pdf version of the Guide is available at: www.gov.mb.ca/agriculture/crops/guides-and-publications/#gfcp

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