Order a combo to conquer glyphosate resistant kochia

Date:12-25-2012

There is good news in the battle against glyphosate resistant kochia.


Research has found that numerous herbicides will kill the pesky plant, but it will be important for producers to vary their use.


Bob Blackshaw, an Agriculture Canada research scientist in Leth-bridge, told a recent Farming Smarter conference in Medicine Hat that preliminary studies show combinations of herbicides in groups 4, 6, 14, 19 and 27 will successfully kill glyphosate resistant kochia. Glyphosate is a Group 9 herbicide.


Blackshaw cautioned that he has only one year of data from one site in a simulated chem-fallow trial. All treatments were a combination of glyphosate and another chemical with a different mode of action.


"What may or may not be a surprise to you is that 2,4-D is not very good on kochia and never has been, either. This is not a resistance thing or anything that has sort of changed. We think of 2,4-D as being good on kochia, but it has often been mixed with something else when we apply it on our fields,” said Blackshaw.


Glyphosate resistant kochia was first identified in Western Canada in 2011 in fields near Warner, Alta. Since then, more has been found near Turin, northeast of Lethbridge, and suspect samples from the Medicine Hat area and southern Saskatchewan are being tested, said Blackshaw.


"It’s probably a little bit more out there than what we think,” he said.


Blackshaw and other researchers collected seed from 300 sites south of the Trans-Canada Highway last fall and hope to get a better handle on distribution of the troublesome weed.


Ninety percent of Alberta kochia is already resistant to Group 2 herbicides, which were developed in the 1980s, and Blackshaw said the recent batch of tests confirmed it.


"The good news is that they were all susceptible to Group 4 herbicides, or most importantly susceptible to dicamba, which is a very good news story for us because … some of the U.S. states already have dicamba resistance, so we’re sort of hoping we’re not there already.”


Blackshaw said he expects many farmers will use dicamba to control kochia, which will work, but he cautioned them to vary their chemical use and use herbicides with different modes of action.


Group 9 herbicides such as gly-phosate are considered to carry fairly low tendencies for development of resistance, said Blackshaw, but frequent use of any herbicide increases the chances.


"We’ve been using glyphosate for a lot of years,” he said.


"We would probably suggest it requires more than 20 applications, but we’re sort of new in the glyphosate story so we don’t really know that. It is a low tendency to develop resistance, but if you use something enough, eventually you may get there with some weed species.”


Kochia is a particularly adaptive weed because it is drought, heat and saline tolerant, is the third most common weed on the Prairies and is a genetically diverse plant that outcrosses.


It also spreads readily as a tumble weed at maturity and produces 10,000 to 35,000 seeds per year. It will germinate at shallow depths in soil temperatures of 2 to 4 C, giving it a head start on most crops, and flushes of the weed can occur throughout the growing season.


Though glyphosate resistant weeds are fairly new to Canada, and particularly Western Canada, Blackshaw said there are 24 resistant species worldwide. Weeds now most likely to develop glyphosate resistance are wild oats, green foxtail and cleavers.


"My message is just be aware, especially when you’re looking at those weeds. If you see something that you think is not right and there’s a chance of resistance, try and let somebody know.”