There are many benefits to a pre-harvest spray application and according to Danielle Eastman, Brand Manager, Western Herbicides and Clearfield at BASF Canada, there are two main reasons why it is important to apply a herbicide pre-harvest.

“The first is to assist with crop dry down and to help provide uniformity throughout the field for an easier harvest. The second is to control perennial weeds.”

Perennial weeds are major competitors to various crops as they consume moisture and nutrients from field crops. Pre-harvest is the best time to control Canada thistle, quackgrass, perennial sow thistle, dandelion, toadflax and milkweed. It’s also important to ensure proper weed staging for the highest effectiveness of a spray application. Dandelions should be at the bud to bloom stage while Canada thistle will need to be at the bud stage or beyond. All target weeds should be green and actively growing at the time of any application.

“Most fields will require a pre-harvest application to remove any variability in the field during harvest and to clean up the field for the next season,” Eastman notes.

Application Timing

Applications should be made when grain moisture is less than 30 per cent. Proper crop staging is crucial to a pre-harvest application. The following guidelines offer a visual indication to help determine maturity:

  • Wheat/Barley/Oat – hard dough stage, a thumbnail impression remains on the seed
  • Canola – Pods are green to yellow and most seeds are yellow to brown
  • Flax – Majority of bolls, 75 to 80 per cent are brown
  • Lentils – Lowermost pods are brown and rattle when shaken
  • Peas – Majority of pods, 75 to 80 per cent are brown
  • Chickpeas – Stems are green to brown; pods are mature; 80 to 90 per cent leaf drop
  • Soybeans – Stems are green to brown; pod tissue is brown and dry
  • Dry Beans – Stems are green to brown; pods are mature; 80 to 90 per cent leaf drop

Application timing is critical. If an application occurs too early yield losses can occur and chemical residues may be taken into the seed, potentially resulting in grain marketing problems.


According to Eastman a pre-harvest application can not only assist in reducing grain moisture, but reduce time to harvest and dry down non-mature plants. “Combining is also easier since the stalks will be easier to feed through the combine,” she explains. A pre-harvest herbicide treatment will aid in a quicker, more efficient harvest as drier plant matter will pass more easily through the combine resulting in lower seed losses.

Knowing the target weed species and application timing are critical for the success of any pre-harvest desiccant or glyphosate application. Crop quality can be increased because the harvest timing after a field has been sprayed is more predictable. If targeting perennial weeds, glyphosate is an effective control measure, and can be tank-mixed with other pre-harvest options to provide broad-spectrum activity. Applying glyphosate in the fall promotes movement of the active ingredient down to the roots, providing more effective control of Canada thistle, perennial sow thistle, field bindweed and dandelion.

Where on the Web

Alberta Agriculture and Forestry and the Government of Saskatchewan offer helpful pre-harvest application Q&As:



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