Posted April 11, 2018 | By: Ernie Nycholat

manager of agronomic services with Nutrien Ag Solutions in central Alberta. Originally published in Grainews, April 10, 2018

Q: What are some considerations when selecting a pre-seed herbicide application?

A: There are significant benefits to applying herbicides prior to seeding or crop emergence. Pre-seed weed removal reduces competition for valuable moisture and nutrients required for seedling development.

When selecting pre-seed herbicides, begin with the crop to be grown. Products available vary considerably by crop. For example for pulses, the products for pre-seed weed control are limited. Pulses can be injured by many herbicides and are poor competitors with weeds. Secondly, identify the weeds present in the field. Scout fields in early spring and review records to know what weed issues are present. It is critical to be aware of all the challenges that need to be addressed.

Glyphosate is the base for most weed control programs, but recently registered Group 14 tank mixes have helped expand weed control. There may be new options every year, but remember the products are crop specific. At one time glyphosate used on its own was the product of choice, but research has shown that tank mixing and using multiple modes of action products provide better solutions, performance and long-term value in managing herbicide resistance.

To make an informed decision on which products to use, know the following:

  • What weeds are present? Herbicide efficacy varies by weed.
  • Are there any winter annuals? Weeds like narrow-leaved hawk’s beard, dandelion and cleavers can establish in fall and are more difficult to kill in spring. For this, there are some very good tank mix solutions.
  • Are there herbicide-resistant weeds? There is considerable concern with the increase in the number of weeds that are tolerant to various herbicide groups, but of major concern is Group 9 or glyphosate-resistant weeds. Glyphosate is the cornerstone of most pre-seed programs and we must be vigilant in its use to delay future weed species becoming tolerant.
  • Is there volunteer glyphosate-tolerant canola that needs to be controlled? Be cognizant of this situation and use appropriate tank mix combinations to control.
  • Are there flushing weeds? In this case a soil residual product may be more beneficial than a straight contact herbicide(s). 

Pre-seed herbicide applications provide a competitive weed-free environment for crops to flourish in the seedling stage. By selecting the right combination of herbicides and applying them correctly, the crops will be off to a great start.


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