By Alice McFarlane

Weed control in the fall successful for winter annuals

Sep 2, 2020 | 2:42 PM

There are several reasons why weeds may be showing up this fall.

A number of fields may have had late applications of herbicides because of the dry spring. Also, slow, and patchy crop growth allowed weeds to get a stronger foot hold.

Saskatchewan Ministry of Agriculture Crops Extension Specialist Kim Stonehouse said fall herbicide applications may be a good way to get control of these weeds.

He said some of the land may have already had a pre-harvest glyphosate application and it hopefully will have good control of winter annuals and perennials. But, if the application was early enough and there is a long fall, control of these weeds can be reduced, and the effectiveness of these pre-harvest glyphosate applications will need to be re-assessed.

Stonehouse said if the efficacy is not good or there was not a pre-harvest glyphosate registration for the crop grown, post-harvest weed control should be considered.

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“Fall is one of the best times for controlling winter annuals such as stink weed, shepherd’s purse, flixweed, narrow-leaved hawk’s-beard, chickweed, and cleavers,” Stonehouse told farmnewsNOW. “Winter annuals are plants that can germinate in the fall then over winter as live plants to get an early start in the spring.

Stonehouse said fall is also a good time to control perennials such as Canada thistle, dandelion and quack grass.

“There are a number of herbicide options for fall weed control. One example is the use of phenoxy herbicides like 2,4-D and MCPA. These can be effective at rates that vary with the difficulty of weeds to control. Phenoxy herbicides also have the advantage of being active at lower temperatures usually extending the window of application,” he said.

Stonehouse said for guidelines on the rates based on formulation and target weeds, farmers should consult the 2020 Guide to Crop Protection and the product labels.

Stonehouse said many producers use glyphosate and for good reason. He said it is another effective option for fall weed control but, it comes with a warning.

“As long as temperatures remain high enough so plants are actively growing, translocation of the herbicide to the root will take place. Events like frost or cutting the weeds during harvest can reduce plant activity. In these cases, a recovery period is required before application,” he said.

Glyphosate tank mixes can be used to enhance the effectiveness on some of the more difficult to control weeds like narrow-leaved hawk’s-beard and cleavers.

“It is important to note that there are re-cropping restrictions for some herbicides,” Stonehouse said.

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alice.mcfarlane@jpbg.ca

On Twitter: @AliceMcF