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Pest Patrol: New herbicide names may not mean new chemistry

#PestPatrol with Mike Cowbrough, OMAFRA

Q: Do I have new opportunities in weed control in 2018?

A: This is the question I’ve been asked a lot this past winter meeting season, and one I always struggle to answer. There are some legitimately promising concepts being tested such as robotic weeders (Figure 1 at top) and weed seed destruction tools, but admittedly most new frontiers in weed management are several years away from being usable on the farm.

Perhaps when people ask this question they are thinking in terms of herbicides. Although there are seemingly many new herbicide names, when you dig down into what active ingredients make up these “new” products, there really isn’t anything new for 2018. A quick way to see for yourself is to search the term “new” in the pest manager app’s “pesticide info” section (Figure 2 below).

Figure 2. By searching the term “new” in the pesticide info section of the pest manager app, one can see all the new products that are in the Ontario marketplace in 2018.
photo: Supplied

With some of the new products, we even go so far as to point out other products that the “new” product is equivalent to. Admittedly, I struggle to keep track of what’s actually in all of the new co-packs and pre-mixed products, and I read more product labels than I care to admit (it’s somewhat depressing). Thankfully the active ingredient compositions of all herbicides are summarized in the pest manager app and the provincial Guide to Weed Control.

Sometimes, though, we do ourselves a disservice by thinking only about what is new. It’s good to remind ourselves of the basic principles to minimize crop losses from weeds. That way, when we’re thinking of making tweaks to our weed management plans, we can make sure that they are consistent with the basic principles which are:

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  1. Always have the crop emerge before weeds do.
  2. Strive to reduce the population density of weeds. The more weeds, the greater the competition against your crop and a higher probability of selecting herbicide-resistant biotypes. Reducing weed density requires multiple strategies including tillage, cover crops, crop rotation (ideally with fall-seeded and perennial crops) and effective herbicides.
  3. Most herbicides should be used to control weeds no larger than the six-leaf stage of growth. If using glyphosate, weeds should be less than 10 centimetres (four inches) tall at time of application (Figure 3 below).
  4. Yield losses are minimized in soybeans when weeds are controlled from soybean emergence until the third trifoliate stage.
  5. Yield losses are minimized in corn when weeds are controlled from corn emergence until the six-leaf over stage of growth.

Figure 3. Believe it or not, this picture of common ragweed, at the six-leaf stage, is the absolute largest it can grow to and still be effectively controlled by a number of herbicides.
photo: Supplied

The 2018 season marks my 17th with OMAFRA. If there are areas that I should be pursuing to better serve you, I would welcome any constructive feedback. Be safe!

Have a question you want answered? Hashtag #PestPatrol on Twitter to @cowbrough or email Mike at [email protected].

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