Mike Cowbrough thinks resistance prevention is an
oxymoron. “If you are using chemical
weed control there is no such thing as resistance prevention, growers need to
focus on resistance management,” says Cowbrough, the provincial weed
specialist with the Ontario Ministry of Agriculture, Food and Rural Affairs.
Cowbrough says the agricultural industry has been
talking about resistance management in weeds for years. “And what conclusions have we come to?” he
asks. There are many cases of resistant
weeds, but most growers only think about it when the problem happens on their
farm. “I understand why growers make decisions the way they do- it’s necessary
to deal with what is in front of them at the time,” says Cowbrough. “But what they need to remember is what we
have learned historically – a lot can change in five or six years.
Cowbrough
encourages growers to think strategically about the reality of weed resistance
developing on their farm. Imagine you
have rented a new field for IP soybeans and have no history of the weed issues-
how would you approach weed control in that field? You would need to develop a management
strategy to cover all variables for weed control – plan for the worst (lots of resistant
weeds) and hope for the best (none).
Developing an approach now will reduce the risk of resistance
development down the road.
Cowbrough recommends:
Rotate chemical
groups. The best strategy, bar none, for delaying the
development of resistant weeds is to alternate the use of herbicides with
different modes of action, as needed throughout the growing season.
Scout for
resistant weeds. After herbicide
applications, scout fields for signs of any persistent weeds. If you find any suspect weeds, identify them
(using web tools listed below) and
consult your local CCA for further management strategies.
Use the
tools. There are a number
of online tools available to help identify weeds and provide resistance
management strategies. Use these tools
to help if you are unable to identify the weed or need further management
information.
www.weedinfo.ca – information and
tools for making informed risk-reducing weed control decisions.
www.weedpro75.com – online herbicide
selection tool focused on profitability and environmental stewardship.
www.mixitup.ca
–
learn
how resistant weed populations develop and key strategies to reduce the risk on
your farm.
Cowbrough isn’t
sure what it will take to bring the practice of resistance management to the
forefront of growers’ minds. It’s human
nature to believe it can’t happen to you…and then be surprised when it
does. Cowbrough continues to look for
new angles to talk to growers about weed resistance, in the hopes that it will
soon start to stick.
If You Suspect That You Have a Resistant Pest
If you think that you may have a resistant pest, contact a crop
specialist in your area. See Chapter 2 - Integrated Pest Management
for ways to contact IPM and Crop Specialists. These specialists will confirm the resistance. They know which pests
in your region are resistant to which Groups of pesticides and they can advise
you on the best Integrated Pest Management (IPM) strategy to use to manage the
resistant pest.
Genetic Testing
Sample Project for Weed Species
A total of 20 genetic tests are available to
identify herbicide resistance in 13 weed species with results provided to you within
the same growing season. Also, two genetic tests for species identification (Amaranthus
and Brassica spp.) are available. If you suspect you have a
herbicide resistant weed and would like to get it tested or if you need to
identify a pigweed species, visit the website of Harvest Genomics for
information about how to collect and submit a leaf tissue sample to their lab
in Guelph. Sample collection kits can be obtained from
kristen.obeid@ontario.ca. Participating in the genetic testing sample project
is free, through project funding.