All that moisture brings something else to fields: weeds

New weed survey Wet fields in 2012 kept Saskatchewan farmers out of fields and let weeds thrive, seeding issues for the 2013 canola crop

A survey conducted last year confirms what Saskatchewan farmers already knew: wet weather contributed to one of the weediest years on record.

Agriculture Canada has conducted the canola weed survey five times: first in 1976 and more recently in 2003. In 2012, the department examined 464 canola fields and found the highest diversity of weeds in the survey’s history and the second highest weed densities.

“I think the take home message is there are weeds that are increasing,” said Agriculture Canada biologist Julia Leeson.

Weeds that have migrated across the province since the 1970s include wild buckwheat, spiny annual sow-thistle, cleavers, barnyard grass, biennial wormwood, foxtail barley and round leaved mallow.

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Almost all of the fields surveyed had weeds present, she told a Saskatchewan Canola Development Commission meeting held during the recent Crop Production Week in Saskatoon.

It was a significant change from the 2003 survey, the first after the 1995 introduction of herbicide tolerant crops, when 40 percent of sampled areas were weed free.

Last year’s wet conditions created less than ideal conditions, kept farmers out of some fields beyond acceptable herbicide application times, boosting weed populations.

“The majority of fields, the weeds didn’t appear to have a major affect on yields,” Leeson said, noting dockage may have been affected.

“A lot of the weeds were under the canopy. You wouldn’t even see them if you just drove by the field.”

The researchers weighed several factors, including frequency and uniformity, to rank weeds based on their relative abundance. Green foxtail, wild buckwheat, wild oats, volunteer wheat and spiny annual sow-thistle topped the list.

There were few surprises at the top of the list.

Green foxtail grows across the province in high densities, and not just in canola, while wild buckwheat and wild oats are also common problems for producers.

Volunteer wheat is related to canola-wheat rotations.

Some species, such as native barnyard grass, marsh cudweed, willow herb and broadleaf plantain, are anomalies, creeping higher on the department’s list than they would in a normal year because of the wet conditions.

Others, such as kochia, which has been a frequent topic of discussion following the discovery of glyphosate resistant biotypes, fell down the list.

“As we get rid of a few of the species that were only there because it was wet, there’s probably a few more things like stinkweed that will make it back up into the top 20, I expect,” she said.

“But once again, the fact that we had this particularly wet year means the seed bank was built up with the species that are there, so the impact of this year will exist next year and for many years coming.”

Leeson offered the following comments on these common weeds in 2012:

Wild buckwheat: “The increase in wild buckwheat isn’t that surprising. Basically we’re looking at a decrease in other broadleaf species that’s allowing room for wild buckwheat to move up. Things like stinkweed aren’t an issue anymore.”
Spiny annual sowthistle: “A less familiar species. It may have been in the past confused with perennial sowthistle, (allowing it to) sneak up without people noticing that it was there. However, it also likely took advantage of the fact that it was wet.”
Cleavers: “It has been increasing and made another jump in 2012. It’s a concern because the cleaver seeds are the same size as the canola seed, making it difficult to separate from canola. This is a species that is definitely spreading.”
Foxtail barley: “Foxtail barley is associated with wet conditions, but the other thing — it’s really been found to be significantly associated with zero till, so I think that’s one we need to watch out for.”