Shuffle your deck before seed goes in the ground
The time is right to sort out crop rotation if herbicide carryover is a concern
It’s been two dry years in a row for many regions across western Canada. But that dryness may be nothing more than a fading memory if you got plenty of rain (or snow!) last fall. Don’t be fooled by that late-season precipitation. It’s not nearly as important as what happened during the key period between June 1 and September 1.
If you didn’t receive four inches of rain during that period, your risk of herbicide carryover increased dramatically. That’s because by September, chemical particles are already bound to the soil, and temperatures cool off, meaning the microorganisms that break down herbicide ingredients are much less active. The same is true in early spring before the soil warms.
Each herbicide manufacturer has taken great pains to help us figure out re-cropping restrictions related to their products. Fortunately, we’re at a key decision point right now where we can still use this information, along with precipitation records, to finalize seeding plans for this year. It’s not complicated, and it’s a much better option than reseeding.
Here are some considerations for folks who may not have had to deal with herbicide carryover before, by active ingredient:
Atrazine (Group 5) – Aatrex® – Should not have carryover on applications of 0.5 L/acre (ac) or less. Most tolerant crops for re-cropping are: up to 1.25 L/ac – corn, millet, flax; up to 0.75 L/ac – peas, soybeans, barley, wheat; up to 0.5 L/ac – oats; and up to 0.33 L/ac – dry beans, canola, sunflower, alfalfa.
Clopyralid (Group 4) - Lontrel™, Cirpreme™, Prestige™, Spectrum™, Salute™, Eclipse™ – Peas and soybeans are safe to grow in rotation after the use of these products EXCEPT when less than 5.5 inches of precipitation is received between June 1 and August 31 the year the product is applied.
Fomesafen (Group 14) – Flexstar®, Reflex® – At 0.23L/ac of Reflex or anything over 0.85 L/ac of Flexstar may have carryover the year following application to soybeans or dry beans. Most crops can be grown the next season EXCEPT for canola, flax, potato, sunflower and alfalfa. An approximate ranking of non-labeled crops from most to least tolerant is: cereals, potato, canola, field corn, sunflowers, alfalfa.
Flucarbazone (Group 2) – Sierra® 3.0 – For areas that got less than 4 inches of rain and have low organic matter, if used 67 ac/jug rate, canola, oats and corn will be sensitive.
- Everest®, Inferno™ Duo – In areas that received less than 4 inches of rain, have low organic matter and high pH soils, field peas will be sensitive.
Imazamox and Imazethapyr (Group 2) – Solo®, Viper®, and Odyssey® – Imazamox has significantly less residual than imazethapyr, but non-Clearfield® canola is sensitive to it. Oats are the most sensitive cereal to imazamox, especially after drought conditions. It may be best to switch into a pulse crop or even a different cereal if last year’s moisture is a concern.
Other factors to consider that affect herbicide carryover along with the amount of precipitation received include; soil pH, low soil organic matter and course textured soils.
Talk to an agronomist if you’re unsure about re-cropping restrictions or how to optimize your rotation to protect this year’s crops.