Preserve Soil Health with Post-Harvest Weed Control

Ahmed Nafea

Sep 20, 2023

Concluding harvest and preparing for winter is an incredibly busy time on most farms. Preparation for the following year remains a priority for most Canadian growers after this year's crop is in the bin. A post harvest herbicide application can be a great way to start planning for the next season. 

Why Farmers Should Spray Post-Harvest 

Post-harvest herbicide application offers farmers a way to control these winter annuals, address perennial weeds, and preserve soil moisture and nutrients for future crops. 

Fall application can also improve grower time management during stressful planting seasons by providing a clean crop free of weeds. By controlling pests and diseases that may still be present in the field after harvest, a fall application will prevent overwintering and reduce problems in the spring. 

Weed control will also prevent weeds from seeding and spreading throughout the field, and reduce competition for nutrients and water, which can improve the yield and quality of the next crop.1

[RELATED: 4 Ways to Minimize Spray Drift]

When to Spray Post-Harvest 

This type of spraying should be done after your crop has been harvested. If you’re spraying any glyphosate tank mixes, you’ll want to do so during the warmest part of the day when plants are most actively growing. 

Ideally, spray on warm sunny days; it’s not advisable to spray right after a frost or before rain. 

If temperatures start to cool, stop spraying 2 hours before sunset and 2-4 hours before the temperature drops below 8℃. Do not apply when there is a risk of severe fall in night temperature after use. Weeds are less likely to grow at these temperatures and herbicide applications will be less effective.2

[READ: Types of Spray Nozzles and How to Choose the Right One]

How to Spray Post-Harvest

To mitigate the risk of potentially developing herbicide resistant weeds, it is important to utilize multiple herbicide groups. Several different post-harvest modes of action are available depending on your specific crops. Consider mixing with Smoke 540 Glyphosate Value Pick ahead of any post-harvest application regardless of crop.

By providing active ingredients from herbicide groups 4 and 9, a tank mix with both Disha 480 and Smoke 540 Glyphosate can help manage herbicide resistance and offer extended weed control into next spring. It will also complement Smoke® 540 glyphosate alone, providing greater control on some harder to kill weeds.

If you’re spraying wheat, barley, corn and canary seed, 2,4-D Ester 700 Value Pick is a good option to control a wide range of tough weeds like perennial sow thistle, dandelions and narrow-leaved hawk’s beard. (Note that growers in Ontario should not apply right before fall wheat or barley.)4

Growers in Western Canada can use Florasulam 50 Value Pick ahead of wheat, barley and oats. This is a good herbicide to control volunteer canola, chickweed, cleavers, buckwheat, Shepherd’s purse, cow cockle and stinkweed.5

Carfentrazone-ethyl 240 EC can be used ahead of many crops. It’s a good option for eastern black nightshade, purslane, kochia, volunteer canola, pigweed and lamb’s quarters.6

The active ingredient in Disha 480 is dicamba and it can be sprayed ahead of cereals, canary seed, soybeans, field corn, sweet corn or white beans. Disha 480 helps control a wide range of weeds including kochia, buckwheat, field bindweed, cleavers and pasture sage. Do not apply before fall seeded crops.7

A good option for growers battling narrow-leaved hawk’s beard, volunteer canola and dandelions is Tribe 75 WDG. It can be used ahead of wheat, barley and SU tolerant canola.

For the control of challenging weeds like Canada thistle, common groundsel, wild buckwheat, volunteer alfalfa and perennial sow-thistle, turn to FBN Clopyralid 360 SL. This is a good option to be used ahead of cereals, corn, flax and RR or LL canola. (Do not apply before pulse crops or non-clopyralid tolerant crops).8

MCPA Ester 600 Value Pick can be used before cereals, flax, grasses and legumes. Susceptible weed range includes burdock (before the 4-leaf stage), cocklebur, plantain, Lamb’s-quarters, mustards (except Dog and Tansy), prickly lettuce, ragweeds, stinkweed, vetch, wild radish, and wild (annual) sunflower. 

[RELATED: Do This Before You Step Foot in the Sprayer]

Prepare for Post-Harvest Spraying with Herbicide Products from FBN Direct®

Post-harvest application is an effective way to control winter annuals and perennial weeds, as they are more susceptible to herbicides at this time. By controlling weeds, growers can help preserve soil moisture and improve soil health for the next growing season.

FBN® offers growers a diverse variety of effective herbicides that will help set you up for post-harvest success, including Smoke® 540, 2,4-D Ester 700 Value Pick and Disha 480.

With direct-to-farm delivery and most deliveries made in three days or less, FBN Direct makes the online ordering process for herbicides and other key products easy and convenient. 


  1. Fall Weed Control Provides Foundation For A Clean Crop, Saskatchewan Pulse Growers, September 2017,, p. 1.

  2. Saskatchewan Pulse Growers, Fall Weed Control Provides Foundation For a Clean Crop, p. 1.

  3. Guide to Crop Protection, Government of Saskatchewan, 2023,, p. 54.

  4. Publication 75A: Guide to Weed Control, Field Crops 2021, Ministry of Agriculture, Food and Rural Affairs, Ontario, 2021,, p. 98.

  5. Government of Saskatchewan, 2023, Guide to Crop Protection, p. 223.

  6. Government of Saskatchewan, 2023, Guide to Crop Protection, p. 148. 

  7. Publication 75A: Guide to Weed Control, Field Crops 2021, Ministry of Agriculture, Food and Rural Affairs, Ontario, 2021,, p. 98.

  8. Government of Saskatchewan, 2023, Guide to Crop Protection, p. 169.

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Ahmed Nafea

Sep 20, 2023