It has been a good year for weeds and with autumn on the western plains, farmers are looking for ways to get a jump on next season’s weeds.
“There are a lot of fields with high weed populations out there this year. Late seeding, rains at spraying time and throughout the growing season have left a lot of weeds in crops. Not to mention the areas where they didn’t get a crop in at all,” said Clark Brenzil, of Saskatchewan Agriculture.
“I expect this year there may be a rediscovery of the lost art of 2,4-D,” said Brenzil.
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The chemical may be popular for its low price and its ability to kill winter annuals that evaded control earlier this season.
“It is still one of the best ways to get control over winter annuals. The later you use it on the winter annuals, the better it will work. Right up to freeze up those plants are susceptible to it,” said Rick Holm, of the University of Saskatchewan’s plant sciences department.
The product will work on perennials as well, but it must be applied earlier and at high rates.
“If farmers are going to use it on dandelion or other perennial weeds, they will need to use a rate of about 16 ounces (per acre.) The trouble is that most weeds like Canada thistle and sow thistle that are tall have been cut down and will need time to grow a bit more before the 2,4-D is effective against them. There needs to be some young healthy leaves to get a good kill,” said Holm.
He said timing for control of perennials is the big issue.
“You need to get to them before they become dormant or there is little point in treating them with herbicides,” he said.
Leaf availability
Brenzil advised producers to leave stubble as high as possible. so younger leaves are available to the pesticide.
He said spraying winter annuals with 2,4-D in the second week of October forces them to grow, drawing nutrient reserves from the root, opening the weed to winterkill.
“Four to six ounces (per acre) should be enough to do the job late in the season,” said Brenzil.
At rates of up to eight ounces, 2,4-D poses little threat to non-cereal crops in the following spring. Even delicate pulse crops are safe, say researchers.
“If you go after perennials with 16 ounces then you can expect to be growing cereals on that land next year,” said Holm.
Farmers considering post harvest applications of glyphosate to control perennial weeds should take note of weather and weed conditions. Glyphosate works best on actively growing weeds. Also, an interval of three to five days between application and a killing frost is needed for greatest control.
“Harvest produces a great deal of dust and if this is still coating the weed’s leaves it will tend to neutralize the (glyphosate) and you don’t get the effect you were looking for,” said Holm.
Herbicides are not the only fall weed control option.
“Sometimes weed control calls for some diesel and steel,” said Steve Shirtlisse of the University of Saskatchewan.
Shirtlisse said chaff collection may be one way to minimize weed seed spread at harvest time.
“It isn’t for everybody. For those who can feed the chaff or have the equipment, it can be effective, but many weed seeds have already hit the ground prior to harvest.”
Chaff collection is most effective in swathed crops and those that can be harvested before the weeds are fully matured, he said.
One of the advantages of collecting chaff is the lack of weed seed spread.
“I have seen it reduce spreading of wild oats and green foxtail from 150 metres down to 30. If you are dealing with herbicide resistant weeds, that is a significant number,” Shirtlisse said.
Harvesting weed patches separately from the rest of the crop and shutting down the threshing and spreading equipment while moving between patches may also reduce spread.
“It is unlikely that most farmers would do this. It’s harvest time and especially if it is late they will need to just get the crop in the bin,” Shirtlisse said.
Burning too broad
Burning can control from 10 to 15 percent of weed seeds, according to research studies in England. But this may interfere with one of the least know methods of weed seed control, insects.
“Critters can eat huge amounts of weeds seeds. In a study in Ontario they removed 32 percent of weed seeds left on the surface of the field,” said Shirtlisse.
The carabid family of beetle is suspected to eat the most seeds through fall.
These insects have been found in Manitoba fields and thrive best in organic and zero-tillage operations.
