If you’re talking early weed control, fall is the earliest you can get for next year’s crop. For many, a pre-harvest glyphosate application does double duty, drying down the crop and setting back those perennials weeds.
But in this incredibly dry year, crop dry-down was so fast many farmers didn’t need to use glyphosate pre-harvest, leaving perennial weeds cut back, but not dead.
What’s your best option for fall control, then? Clark Brenzil, weed management specialist for the Saskatchewan Ministry of Agriculture, says that while fall is a great time to hit perennial and winter annual weeds, we’re a good six weeks out from a fall application.
Brenzil says that the dry conditions opens up the spectrum on what products you can use, but “you need to adjust your thought process on your glyphosate rates and what you have to do to make that successful.”
You need enough top re-growth to make the application worth it, Brenzil says, but you also need to triple your glyphosate rates. Why? Because the re-growth we do get still will amount to much less surface area that we would have targeted pre-harvest. You need more active ingredient — about 1,000 g/acre — to ensure that limited leaf area intercepts enough product, he says.
Brenzil says that in a dry cycle, it’s doubly important to get control on winter annuals and perennials, as they’re big water users and will be up well ahead of the crop next spring. If the dry bias continues, that’s precious moisture that should be left for seedlings.
That said, if this fall continues to be very dry, you may not get enough top growth to make a pass worth it, such as the case with sow thistle that could simply shut down into early dormancy because of a lack of rain. Make sure you scout and take note of the weed types before you climb into the sprayer
What about fall tillage to move residue around? Will that help or hinder the fall weed control strategy? Brenzil says that, to have an impact on weed seed gemination, you need to break the soil surface — and that’s going to cause moisture loss and leave soil vulnerable to wind erosion. What’s more, stubble traps snow — a rather important spring moisture source. Unless you need to incorporate a soil-applied herbicide, such as Edge or Treflan, leave the soil be.
Brenzil adds that herbicide carryover is likely to a big risk for sensitive crops heading in to 2019 (read more on that here), and, in the audio below, he adds some tips for weed timing for fall seeded crops, as well.