Herbicide resistance is becoming more predominant across Canada as Group 2 herbicide resistance is on the rise. For crops such as peas, this can be problematic because of the dominant use of Group 2 herbicides. There are several Group 2 herbicides on the market but more specifically peas have a very narrow spectrum of what broadleaf herbicide can be applied on them. Applying a multi-mode action herbicide or two herbicides with different groups can increase the chance of controlling the Group 2 resistant cleavers. Moreover, in North Western Saskatchewan, the majority of peas grown are semi-leafless which makes them less competitive against weeds for nutrients. Nonetheless, there are still struggles that arise with selecting the appropriate herbicide in peas as many have recropping restrictions on them. This leads to rotation difficulties over the years as many Group 2 herbicides, like Odyssey, have recropping restrictions intervals of 12 months for Clearfield Canola, spring wheat, spring barley and lentils.
In the North Western region of Saskatchewan many times we see a fluctuation in organic matter (OM) in our soils. When dealing with lower organic matter (<6), a Group 14 herbicide worked well coupled with a Group 2 herbicide. However, some of the Group 14’s used have yet to be registered for control of cleavers. Any soils with an OM >6 may require more attention and time; Group 14 herbicides did not seem effective on OM >6 until a significantly high rate was sprayed. This is not economical for many farmers so there are several options that can be done:
- Fall applied Group 3 by spring pre-emergent Group 14
- Fall applied Group 3 followed by spring post-emergent Viper ADV
- Spring pre-seed Heat followed by post-emerge Viper ADV
Although these options require more time in the sprayer, the benefits can be seen in yield increases for peas. Group 2 resistant cleavers are slowly making their way to our area, field management should be monitored to help decrease the risk of more Group 2 resistant weeds being selected. Other ways to help control the amount of Group 2 herbicide resistant weeds includes:
- Use different herbicides
- Do not overuse same mode of action
- Crop rotations
- Increase seeding rate (to increase competition with weeds)
- Soil test and use proper Fertility
- Keep equipment clean
Studies are now being done on a new Group 15 herbicide that has been successful in Australia. Pyroxasulfone is a soil-applied herbicide that can be used in the fall or in the spring pre-seeding or pre-emergence. Pyroxasulfone is currently registered for use on field corn and soybeans in Canada. Hopefully over the next few years pea growers will have another option to rely on.