(file photo/The Canadian Press)

By Alice McFarlane

Weed Control

Pre-emergent weed control

Apr 12, 2019 | 4:54 PM

A significant number of volunteer canola seeds may have been added to the existing weed bank because of the delayed harvest last year.

Ministry of Agriculture Crops Extension Specialist Kim Stonehouse said the benefits of pre-emergent weed control can be significant. Spring applications give more options to rotating herbicide modes of action reducing the risk of developing, and controlling existent herbicide resistant weeds.

“Pre-emergent weed control can be broken down in to two types: pre-emergent soil applied and burn-down applications. Many product choices exist within each category. With soil applied herbicides there are a number of products that offer control of group one and two resistant grassy weeds but there are only a couple that offer control of broadleaf weeds including group two and nine resistant kochia,” Stonehouse said. “All have restrictions on the type of crop that can be grown after application and many have varied rates or restrictions for organic matter and clay content so consulting the label is important.”

With pre-seed burn-down applications, glyphosate is the main product in this group. There are a number of options that can be used in combination with glyphosate to minimize the development of herbicide resistance and allow for control of the round-up ready canola volunteers.

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“If group two resistance is already a problem, it is essential to determine which products have the potential to control these weeds and which do not. Some of the products also have residual effects so it is important to pay close attention to the labels and make sure they are registered for use prior to the crop planned for that field,” Stonehouse said.

“Pre-seed burn-down has the advantage of controlling the weeds already growing so you can pick the product you need based on the weed spectrum present. Weeds should be actively growing for the best results. Glyphosate applications are always more effective when temperatures are above eight degrees Celsius with no overnight frost in the forecast and in bright sunlight,” Stonehouse said. “As well, some products or combinations of products may require higher water volumes so it is important to pay close attention to this because of potential hard water antagonism of the glyphosate.”

Stonehouse said if the opportunity presents itself to apply some pre-emergent weed control it will be important to choose the right product or combination of products to reduce the risk of developing herbicide resistant weeds and prevent early weed competition that may not be possible with in-crop applications.

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alice.mcfarlane@jpbg.ca

On Twitter: @AliceMcF