The Prairie Giants Crop Report

Field observations at your fingertips

May 2, 2022

Taylor Kurtenbach

How to Cost-Effectively Use Your Glyphosate
With prices 2.5x as high as they were last year and market uncertainty, it is as important as ever to use our glyphosate efficiently, both agronomically and for the pocketbook.

The addition of ammonium sulphate (AMS) is a cost-effective method to increase the effectiveness of your glyphosate. Hard water contains calcium and magnesium ions that tie up with glyphosate making it less effective. When you add AMS the sulphate ion binds with the calcium and magnesium ions preventing them from tying up with glyphosate. The ammonium binds to some of the glyphosate molecules which is believed to improve its effectiveness on some weeds[1]. AMS should always be added to the tank first. Rates vary depending on the water source, but 1% volume for volume is a general rate[2]. Another way to minimize the effect of hard water on glyphosate is to reduce the water volume used[1]. The less water, the less amount of calcium and magnesium ions present. Glyphosate is just as effective at 5 gallons per acre as it is at higher water volumes. This is the only time we will tell you that less water is better.
Symptoms of glyphosate

Symptoms of glyphosate

Symptoms of glyphosate

Symptoms of glyphosate

Applying only the necessary rate to control the weeds present is another way to get the most value out of your glyphosate. The following chart is adapted from the Manitoba Guide to Field Crop Protection.
Application RateWeeds ControlledWeed Stage
180 grams ai
0.5 REL
Annual grasses

Lady’s-thumb, stinkweed,
non-RR volunteer canola, wild mustard,
cleavers, flixweed, hemp-nettle,
lamb’s quarters, redroot pigweed,

Narrow-leaved hawk’s-beard

Wild buckwheat

< 6” tall

< 3"

Cotyledon to 2-leaf
275 grams ai
0.75 REL
Above weeds PLUS

Narrow-leaved hawk’s-beard

Wild buckwheat

3" - 6"

3 to 4-leaf
325 - 360 grams ai
Above weeds PLUS

Annual sow thistle, kochia,
shepherd’s purse


< 6" tall

< 6" diameter
540 grams ai
1.5 REL
Above weeds PLUS


> 6" diameter
Perennials such as dandelions and Canada thistle are best controlled in fall with a pre- or post-harvest application.

For spring applications, tank-mixing glyphosate with a pre-seed product can help you get the best control while also using a reduced rate. Majority of products are registered to be tank mixed with glyphosate at 0.5 REL and control tough to kill weeds that usually require a higher application. For example, applying florasulam + glyphosate at 0.5 REL in front of cereals controls large dandelions whereas spraying glyphosate alone would require rates up to 1.5 REL.

Adding a tank mix partner with glyphosate not only aids in weed control (especially on those that glyphosate may be weak on, such as wild buckwheat and dandelions[3]), but it also controls round-up ready volunteers and combats resistance. Although glyphosate is considered in the low-risk category for herbicide resistance, it does occur. This is due to the adoption of zero-till, multiple applications in a season (pre-seed, pre-harvest, post-harvest) and glyphosate resistant crops[4]. In Canada, there are currently six glyphosate resistant weeds (giant ragweed, Canada fleabane, common ragweed, waterhemp, kochia and downy brome)[4], two of which occur in Manitoba (waterhemp, kochia). It is also likely that wild oats will develop glyphosate resistance in the future[5]. In order to combat resistance, both modes of action need to act on the same weed.

Here at Prairie Giants Crop Supply, we are a Defy Resistance Headquarters – your one-stop shop for dealing with herbicide resistance. Click the link ( to check out the site for more resources including a Resistance Guide.

Reach out to the crew at Prairie Giants with any questions on how we can help to get the most
out of your glyphosate application!
[1] Isleib, J. 2011. July 8. Do I Really Need to Add Ammonium Sulfate to My Glyphosate Spray Mix? Michigan State University. [Online] Available:
[2] Wolf, Tom. 2021. November 18. Dealing with Pesticide Shortages in 2022. Sprayers 101. [Online] Available:
[3] Pilger, G. 2013. March 20. Pre-seed Burn-off Herbicides. Grainews. [Online] Available:
[4] Geddes, C. 2018. January 9. Glyphosate Resistant Weeds in Western Canada. Agriculture and Agri-Food Canada. [Online] Available:$Department/deptdocs.nsf/all/crop16553/$FILE/charles_geddes.pdf
[5] Jones, T. Herbicide Resistance in Manitoba. Manitoba Pulse and Soybean Growers. [Online] Available:

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