By Charles GeddesVariable weather during spraying season this year helped some weeds escape herbicide control. These weeds can be misidentified as being herbicide-resistant, when in fact poor weather conditions during or after herbicide application were the cause. However, with a growing number of cases of herbicide-resistant weeds, herbicide-susceptibility can no longer be assumed; even in a year where ideal conditions during spraying were few and far between. A false assumption of herbicide-susceptibility can result in uninformed weed control decisions next year, and even large losses in profit or further spread of herbicide-resistant weed biotypes.
Several entities exist to help growers stay
on top of their herbicide-resistant weeds. Diagnostic testing labs like the
Crop Protection Lab, Pest Surveillance Initiative, or Ag Quest, among others,
provide routine diagnostic testing for known herbicide-resistant weed biotypes
(find more information here: https://www.canolawatch.org/2013/01/31/agriculture-labs/).
Testing can help inform growers of herbicides which remain effective on a
resistant weed biotype, or help confirm that a weedy escape was in fact due to a
herbicide miss or weather event. Growers are encouraged to take advantage of
these resources and have their weeds tested for resistance. Some diagnostic
labs offer testing for a broad range of herbicide and weed species
combinations; but in general, these tests are limited to known cases of
resistance found previously in western Canada.
Mutations resulting in herbicide
insensitivity are a natural, but rare, phenomenon, and selection pressure
imposed by recurrent herbicide application results in an increase of resistant
weed biotypes in the weed population over time. Efforts in discovery,
surveillance, and monitoring are necessary to stay on top of herbicide resistance.
Herbicide resistance affects the farming community as a whole, not just
individual farms; and thus the impacts of identifying a potentially resistant
weed extend beyond the farm boundary. Early discovery of a herbicide-resistant
weed biotype can aid in eradication efforts and limit the impact or spread of
resistant weeds on or off the farm.
Discovery of novel herbicide-resistant weed
biotypes requires more in-depth experimentation than routine diagnostic
testing, meaning that it is considered research. The Prairie Herbicide
Resistance Research Lab at AAFC-Lethbridge can help with identification of new
types of resistance at no charge to the grower. This research lab will test
weed samples using a series of experiments, which can aid in early
identification of novel resistant weed biotypes. Growers are encouraged to
contact Dr. Charles Geddes (Charles.Geddes at canada.ca) if they suspect they
have a type of herbicide resistance which is uncharacterized in the Canadian
Prairies. Testing requires viable seed, so samples must be collected either
pre- or post-harvest depending on the weed species.
Some examples of weeds on the watch list
Created October 7, 2019 | Category: Pest Management