his three-part series will examine best practices and common weed management questions asked by farmers producing food-grade, non-GMO soybeans.
Best practice #1: Budget for two herbicide passes, and hope you only need one
The past decade of research trials has shown that “one-pass” post-emergence herbicide programs have resulted in poorer weed control (by 12 per cent) and lower yields (by 20 per cent) when compared to effective “one-pass”, soil-applied herbicide programs.
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When a soil-applied herbicide controls all the weeds that you have on your farm, and does so throughout the critical period of weed control (from 1st to 3rd trifoliate stage), you lose money by also applying a post-emergence herbicide (Table 1 below).
However, it’s best to budget for a second pass through the field. Most growers will experience some level of failure with a soil-applied herbicide. There are many reasons why they can fail. Insufficient rainfall to activate the herbicide has historically been the main culprit. But it’s not uncommon to get a late flush of seedling weeds just as the residual activity of the soil-applied herbicide dissipates. In most fields, a second pass with a post-emergence herbicide is needed to achieve season-long weed control and to minimize weed seed production and dispersal.
The economics support a second application when the pre-emergence herbicide fails to provide acceptable control and seedling weeds have emerged within the 1st to 3rd trifoliate stage of soybeans (Tables 2 and 3 above).
Next article we will compare the strengths and weaknesses of various soil applied herbicide programs as well as their compatibility with “burn-down” herbicides.
Have a question you want answered? Hashtag #PestPatrol on Twitter to @cowbrough or email Mike at [email protected].
