With harvest activities starting to wrap up in some areas, farmers are looking at their fall weed control. 

Weed Control Specialist Clark Brenzil says weeds need to be actively growing in order to get the best result. 
Fall weed control or suppression is helpful to prevent the plants from flowering and setting seed prior to the crop coming up in the spring.

For perennial weeds you're looking at trying to control things like Canada thistle, dandelion, quackgrass and potentially foxtail barley in the fall.

Brenzil says for Canada thistle the ideal time for control is with a pre-harvest treatment of glyphosate.

"That's because you're looking at about a litre or about 360 grams of active ingredient per acre for that application. Whereas, if you go to a post-emergent application, you have to pretty much triple that rate in order to get the same amount in the plant, just because you've got proportionately less leaf area on that plant."

He says fall is a perfect time for control of dandelions using things like 2-4-D, tribenuron or even florasulam products.

Trials have shown that those products applied in the fall, followed by a spring burn-off have proven to be pretty effective on things like dandelion.

Brenzil says that's a good way to preserve a little bit of budget on glyphosate and utilize some of the other products that are available.

Fall is also a good time to target winter annuals.

He points out that a fairly light rate of 2-4-D as late in the fall as you can go will do a very good job of controlling things like stinkweed, flixweed, shepherd's purse, and a range of other weeds even kochia.

"We were doing some of this work when I was working with the University. Doing some of these fall applications, especially under conditions where it was particularly dry, and thinking at the time why are we putting these treatments down because it's really not going to make any difference. But, it was surprising the difference that it made coming out of winter and into spring as to how much Kochia was in those plots. The 2-4-D actually worked quite well at suppressing the growth of new Kochia first thing in the spring."

Brenzil notes that producers would normally consider glyphosate because for the last couple of decades it has been fairly cheap, but we're seeing higher glyphosate resistance showing up now in kochia, and even in downy brome in southern Alberta.

Another thing to consider in the fall is application of some of those soil active products that would provide in-crop weed control going into the crop for next year.

He adds Thanksgiving weekend prior to freeze up is probably a good timeline if you're looking at a surface application with a light incorporation with a harrow.

Essentially, the research would show that you get better control in those situations, because you've allowed more of those plants to germinate leading up to the freeze up period.