Features Agronomy Weeds
Wet acres from 2010 leave 2011 weed problems

The lasting effects of wet acres in 2010 will start showing up when the ground thaws out. In many parts of the Prairies, wet acres meant unseeded or flooded acres, missed herbicide applications, and the chance for weeds to flourish. “From what I saw in 2010, because farmers couldn’t get out on the field early enough, if they could at all, a lot of weed growth didn’t get sprayed,” says University of Saskatchewan research assistant Ken Sapsford. “There were a lot of perennials like dandelion, sow thistle, Canada thistle and foxtail barley that really took off.”

Sapsford explains that where growers were able to get on the field for a chemfallow treatment on unseeded acres, they were able to achieve excellent control of Canada thistle, quackgrass and foxtail barley, but dandelion had already set seed. “There will be dandelion all over the country in 2011,” says Sapsford.

Curled dock is another perennial weed that made an appearance on wet soils in 2010. It is a prolific seed producer and thrives in wet soils. Sapsford says curled dock usually can be found in sloughs and wet areas, but in 2010, it was found in many areas across entire fields. Most Group 4 products will control curled dock in cereals. “In south Saskatchewan, curled dock was showing up all over the place.”

Jon Gough, DuPont Canada product manager for cereal crops, says feedback from the field was similar to what Sapsford saw. “The perennials certainly thrived in 2010. If farmers were able to get in with a tillage operation, they were able to control some of the dandelions, but there will be issues on those acres where tillage or chemfallow was either delayed or missed.”

Cattails were common on flooded land, but Sapsford says not to worry; once the land dries up, the cattails will not survive.

Another unique weed identified a couple times in Saskatchewan was marsh willow herb. Like cattails, it is typically found in low lying and wet areas, so Sapsford does not expect it to be a problem when the soil dries out.

Sapsford says the persistent wet fall weather in 2010 also meant many farmers missed their post-harvest herbicide application. Post-harvest would have caught up on weed control from the summer, but the missed application means winter annuals will be waiting in the spring, and likely be large and difficult to control.

Be prepared early
An early preseed burndown will lay the foundation for most acres, if farmers can get on the field early. Sapsford advises to go after winter annuals with a residual product where it fits into the crop rotation.

Prior to cereals, Sapsford recommends a glyphosate/Express SG or Express PRO tank mix or PrePass. Express PRO gives extended control of winter annuals, germinating spring annuals like cleavers, narrow-leaved hawk’s beard (both can be winter annuals as well) and volunteer canola, and perennials like dandelion. As a preseed burndown, Express SG can be applied up to 24 hours prior to seeding spring wheat, winter wheat, durum, barley, oats, canary seed, and, depending on soil type, most pulse crops.

Amitrol, CleanStart and glyphosate are registered for preseed burndown immediately prior to canola and most pulses. “Some of the perennials don’t come up early, like Canada thistle and sow thistle, so you won’t be able to control them with a preseed application. You’ll have to look at in-crop options,” says Sapsford.

Another consideration is weed size at preseed burnoff. If fields are wet and application is delayed, Sapsford recommends bumping up the rate. “With the price of glyphosate, don’t skimp on it, go with higher recommended rates when weeds are larger.”

Gough says Express SG and Express PRO have proven to be very good at controlling Roundup Ready canola varieties and other hard-to-control weeds with some flush control into the season. He is concerned that spring tillage used to dry out the soil or smooth out ruts will stimulate germination of annual weeds and spread perennial weeds around.

Crop rotations will dictate in-crop options
On fields where perennial thistles thrived, Sapsford suggests growing cereals or herbicide-tolerant canola. Cereals are competitive and some herbicides provide good suppression. Thistles can be suppressed in herbicide-tolerant canola as well. “Perennial broadleaf weeds will have a free ride in pulses,” says Sapsford.

For foxtail barley, Sapsford says research has found higher rates of Assure II provide suppression in pulse crops. 

Looking at annual weeds, Sapsford recommends assessing the worst weeds and also using those as a guide for crop choices. “Broadleaf weeds are controlled more easily in cereal crops, and grassy weeds are controlled more easily in broadleaf crops. Weeds aren’t the only consideration in crop rotations, but assessing your weed problems along with crop rotations can help with weed control.”

Gough says the new DuPont Barricade herbicide, registered in 2010, provides another option for wheat and barley growers. It combines three active ingredients in two herbicide groups (Group 2 and 4) to provide wide spectrum broadleaf weed control including cleavers and kochia, and control of Group-2 resistant weeds. “Barricade stacks up well against virtually any cereal product in the market today including Infinity, and is priced very competitively. It has a wide window of application, which helps when the weather is against you, easy-to-handle package size, and very flexible recropping options,” says Gough. 

Lingering perennial weed problems may also need to be cleaned up with pre- or post-harvest applications. Sapsford says cleaning up fields may take a concerted effort during the next year to 18 months, if Mother Nature allows. “There are a lot of wet fields, and with an early snowpack, there are fears that seeding will be delayed or some acres will go unseeded a second year. Hopefully a normal year will help farmers get on top of their weed problems,” says Sapsford.