Resistant weeds are becoming the new norm in weed management for many Ontario farmers. This is a reminder that genomic resistant weed testing will be available again at no cost to the grower due to funding from the Fresh Vegetable Growers of Ontario, the Ontario Processing Vegetable Growers, Bayer Crop Science Canada, and Syngenta Canada Inc. It is important to get suspected resistant weeds tested on a field-by-field basis. This ensures that you have a resistance profile for each field.
There are now 26 different genetic tests available to Ontario growers, plus two species differentiation tests. The Amaranthus species differentiation test has been instrumental in identifying waterhemp and hybrids of waterhemp with other pigweed species.
In Ontario there are 22 different herbicide-resistant weed species. The common trend is that there are more species that are multiple herbicide-resistant, or resistant to more than one herbicide group. Of particular concern is waterhemp that has been found to be 5-way resistant to herbicide groups 2 (Prism, Pinnacle, Pursuit), 5 (Lorox, Gesagard, Sencor, Sinbar), 9 (glyphosate), 14 (Authority, Chateau, Eragon, Valtera) and 27 (Armezon, Callisto, Laudis, Shieldex) in 7 counties in Ontario – Chatham-Kent, Elgin, Essex, Lambton, Middlesex, Northumberland and Stormant/Dundas/Glengarry. This brings the total Counties with herbicide-resistant waterhemp in Ontario to 18. Waterhemp is no longer just a field crop problem, it has also been found in several horticulture crops – asparagus, peppers, and sweet corn.
With genetic testing we do not have to wait for the weeds to go to seed, we just need a piece of leaf tissue about the size of a quarter from 10 different plants in the field. So as soon as you notice your herbicide not working, take the samples. This can occur right after planting or anytime throughout the growing season.
Why is it so important to get your weeds tested? It’s simple, the number and distribution of herbicide-resistant weeds in Canada is increasing rapidly in all crops and the cases of multiple herbicide resistance are becoming the new norm. These tests can be completed in under 2 weeks. Having diagnostic tests available to quickly confirm the presence of herbicide-resistant weeds will improve the timeliness of management and prevent their spread which will increase the lifetime of current herbicides for as long as possible.
Our only defense against herbicide-resistant weed species is to scout for and test suspected populations as soon as possible.
To obtain sample collection kits and protocols please contact: Kristen Obeid, OMAFRA Weed Management Specialist for Horticulture Crops on twitter @WeedProfesh, by email: kristen.obeid@ontario.ca or text or cell 519-965-0107.
Genetic Tests Available
| Weed Species | Herbicide Group (s) | Common Herbicide Trade Name (s) (provided ONLY as example herbicides commonly used in horticulture) | Target Site Mutation / Metabolic / Species Identification |
| Amaranthus species | – | – | Species Identification |
| Brassica species | – | – | Species Identification |
| Brassica species | 9 | Glyphosate | Presence of transgene |
| Canada fleabane | 9 | Glyphosate | Target-site (P106S) |
| Common chickweed | 2 | Pinnacle, Prism, Pursuit, Sandea | Target-site (P197Q & unpublished) |
| Common ragweed | 2 | Pinnacle, Prism, Pursuit, Sandea | Target-site (W574L) |
| 5 | Atrazine, Lorox, Sencor, Simazine, Sinbar | Target-site (V219I) | |
| 9 | Glyphosate | Target-site (P106S sequencing assay) | |
| 14 | Blazer, Reflex | Target-site (R98L & R98Q) | |
| Eastern black nnightshnightshade | 2 | Pinnacle, Prism, Pursuit, Sandea | Target-site (A205V) |
| Giant foxtail | 2 | Pinnacle, Prism, Pursuit, Sandea | Target-site (unpublished) |
| Giant ragweed | 2 | Pinnacle, Prism, Pursuit, Sandea | Target-site (W574L) |
| 5 | Atrazine, Lorox, Sencor, Simazine, Sinbar | Target-site (V219I) | |
| 9 | Glyphosate | Target-site (P106S sequencing assay) | |
| Green foxtail | 2 | Pinnacle, Prism, Pursuit, Sandea | Target-site (unpublished) |
| Green pigweed | 2 | Pinnacle, Prism, Pursuit, Sandea | Target-site (S653N & W574L) |
| 5 | Atrazine, Lorox, Sencor, Simazine, Sinbar | Target-site (A251V, S264G, V219l & F274L) | |
| 14 | Aim, Authority, Blazer, Chateau, Goal, Reflex | Target-site (ΔG210 in PPX2L & R128I) | |
| Italian ryegrass | 9 | Glyphosate | Target-site (P106S) |
| Lambs-quarters | 5 | Atrazine, Sencor, Simazine, Sinbar | Target-site (S264G) |
| Large crabgrass | 1 | Assure, Poast Ultra, Select, Venture | Target site (ACCase gene over expression) |
| Redroot pigweed | 2 | Pinnacle, Prism, Pursuit, Sandea | Target-site (S653N & W574L) |
| 5 | Atrazine, Lorox, Sencor, Simazine, Sinbar | Target-site (A251V, S264G, V219l & F274L) | |
| 14 | Aim, Authority, Blazer, Chateau, Goal, Reflex | Target-site (ΔG210 in PPX2L & R128I) | |
| Waterhemp | 2 | Pinnacle, Prism, Pursuit, Sandea | Target-site (S653N & W574L) |
| 5 | Atrazine, Sencor, Simazine, Sinbar | Target-site (A251V, S264G, V219l & F274L) | |
| 9 | Glyphosate | Target site (EPSPS gene amplification) | |
| 14 | Aim, Authority, Blazer, Chateau, Goal, Reflex | Target-site (ΔG210 in PPX2L) |
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