Despite depressed prairie farm incomes this year, farmers should carefully weigh the benefits of investing in weed control.
Weeds are back for the fall and some of the best money spent this season may be on control for next spring.
Russ Horvey, of Alberta Agriculture in Three Hills, said despite the shortage of money available for weed control this fall, it may be the most efficient time to gain the upper hand over perennials and winter annuals.
“Everybody’s got them and they can be real yield destroyers, especially when moisture is at a premium,” he said.
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“An effective blow against thistle and dandelion” is possible if glyphosate herbicides are applied before heavy frosts damage the cellular structure of the leaves, said Horvey.
He said producers might wish to wait for “a light shower” to clean the harvest dust from the leaves so that it doesn’t interfere with pesticide uptake.
“That can be a gamble though. If you get those hard frosts first you lose the advantage of getting the Roundup into the plant,” he said.
In the driest areas, many of the weeds that could normally be controlled in the fall have suffered as much as the crops.
Steve Shirtliffe of the University of Saskatchewan says it depends on the conditions of those plants whether it will pay to spray.
“Quackgrass. If the leaves are already off the plant due to the drought then there isn’t much point in going out there with 2,4-D. You can’t treat a stick with herbicide and expect any benefits next spring,” he said.
Rick Hold from the U of S Crop Development Centre agrees.
“Fall rains could change all that. Then controlling those winter annuals with 2,4-D will pay. You want big green healthy plants if you going to get a good kill,” he said.
Strong moisture conditions were present in northern Alberta and the eastern Prairies, but weed control poses challenges in those areas.
John Hoffman, Alberta Agriculture agrologists in the Peace River district said good fall weed control often comes in the form of pre-harvest applications of glyphosate.
“Most of it is done for this year, but applications of 2,4-D later in the season can really help with control of winter annuals. Often in the spring it is too wet first thing to get out and control these weeds. They’ve had a good head start and they are tougher to kill by then. It is easier to get them in the fall,” he said.
Holm said zero-till growers can usually expect reliable winter annual kills with glyphosate spring burn-off but control of dandelions and thistles may not be as effective at that time because those weeds often emerge after the crop is seeded.
“Those are best controlled with pre-harvest spraying but that window is closed for this season. If they are still growing right now, then glyphosate can be very effective in the fall as long as the plant is still transferring those sugars to the roots,” he said.
“Then you hope for a week of good weather after you spray to get that herbicide all the way into the roots,” he said.
Farmers who are treating winter annuals such as flixweed and stinkweed can expect good fall control with low rates of 2,4-D up to four ounces to the acre. Weeds such as narrow-leaved hawksbeard and shepherd’s purse require higher rates. Rates closer to 16 oz. are necessary for control of dandelions and thistle, say agrologists.
At rates below four oz. residues are unlikely to affect spring-seeded lentils, canola or other spring-seeded crops.
“I you are treating with anything higher than the lowest rates then you should stick to cereals in the spring,” said Holm.
“If we get some rain in the drought-affected areas then there are great benefits to be had in fall weed control, but for now those producers would do better to wait,” he said.
Hoffman warned producers in areas with heavy crops to beware of residues in any post-harvest application of herbicide.
“If the weeds are covered with a blanket (of residue) then you won’t be able to get the herbicide onto the leaves as easily and that will cause problems,” he said.
Horvey adds that lower water volumes should be used with glyphosate herbicides and higher volumes with 2,4-D.
“If you have to get through a heavy canopy then you need the higher water volumes and the 2,4-D will work better at those rates. Then Roundup will be better at lower rates where dissolved solids in the spray water don’t impede the herbicide,” said Horvey.
