GROUP 27 HERBICIDES
A powerful herbicide resistance tool for Western Canadian growers
In the ongoing battle against herbicide-resistant weeds on the Prairies, Group 27 herbicides have become an increasingly important weapon in the herbicide toolkit. Understanding how they work — and how to use them responsibly — is essential for any Western Canadian producer.
The first Group 27 herbicide registered for use in Western Canadian cereal crops arrived in 2007 and was hailed as the first new mode of action introduced to the cereal herbicide market in North America in roughly 20 years — a significant milestone for Prairie growers facing escalating herbicide resistance challenges. Now that the mode of action has been in the system for over a decade, we are seeing more products with greater added benefits, such as the addition of tolpyralate in Corteva Agriscience’s OnDeck herbicide, that will continue to increase its value.
How Group 27 Works
Group 27 herbicides inhibit enzyme 4-hydroxyphenylpyruvate dioxygenase, better known as HPPD. This enzyme plays a critical role in the production of carotenoids — the pigments that protect plant cells from light-induced oxidative damage. When HPPD is blocked, carotenoid synthesis shuts down, chlorophyll is rapidly degraded, and new plant tissue turns pale white or yellow in a characteristic symptom called bleaching. Without the ability to photosynthesize, susceptible plants die within one to two weeks of application. Because this mode of action targets a biochemical pathway distinct from Groups 1, 2, or 4, Group 27 products are a valuable resistance management option.
What Weeds Does It Target?
Group 27 products excel at controlling broadleaf weeds. In Western Canada, they are particularly valued for their efficacy on tough-to-kill species including kochia, wild buckwheat, cleavers, and Canada fleabane — several of which have developed resistance to other herbicide groups. The bleaching symptom typically appears within days of application, giving producers a visible early indicator that the product is working.
Products Available in Western Canada
At this point, the range of Group 27 products is limited, but Corteva’s OnDeck has quickly become an important tool for Western Canadian growers. Corteva's OnDeck combines tolpyralate (Group 27) with bromoxynil (Group 6), pairing two distinct modes of action to improve both efficacy and resistance management and is particularly valued for its efficacy on kochia, wild mustard, wild buckwheat, and volunteer canola, as well as green and yellow foxtail.
Restrictions to Be Aware Of
Growers should be mindful of rotational restrictions, particularly where pulse crops follow cereal crops treated with Group 27 herbicides. Soil characteristics such as low organic matter and high pH can affect herbicide persistence and increase the risk of carryover injury to sensitive crops like lentils and peas. Always consult the product label and provincial guides before application.