Pest Patrol: How do I get better control of lamb’s quarters?

#PestPatrol with Mike Cowbrough, OMAFRA

Lamb’s quarters has consistently been identified as the most abundant and most problematic weed affecting field crop production in Ontario. Yet the Pest Management Regulatory Agency database contains hundreds of herbicides that list lamb’s quarters as either suppressed or controlled.

It’s safe to say there is an arsenal of products available to farmers, but our focus should be on putting them in a position to work well. Since control of lamb’s quarters can be variable, there are obviously several factors that affect herbicide performance.

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Here is my checklist. It certainly applies to other weeds too, but for now let’s focus on maximizing control of common lamb’s quarters.

Checklist to maximize lamb’s quarters control

  1. Implement farming practices that improve soil health (e.g. soil organic matter) and encourage beneficial micro-organisms (e.g. 30 per cent residue cover, conservation tillage, cover crops, crop rotation, judicious use of insecticides and fungicides).
  2. Use soil-applied pre-emergence herbicides. The germination window of lamb’s quarters is several weeks and typically requires two herbicide applications for best control. A soil-applied herbicide will protect grain yield while the post-emergence application will minimize weed seed production (see Figure 2 at bottom).
  3. Apply glyphosate before lamb’s quarters gets taller than five cm (two inches) or before the six- to eight-leaf stage for most other post-emergence herbicides (see Figure 1 at top).
  4. Apply post-emergence herbicides when ambient air temperatures are above 20 C.
  5. Apply post-emergence herbicides during the day, between 6 a.m. and 6 p.m.
  6. Avoid tank mixing micronutrients with herbicides.
  7. Condition carrier water when its pH is beyond extreme ranges (<5 and >8).

The above is an excerpt taken from the new book A Guide to Problem Weed Control in Ontario, available from late February 2017 at and at the 2017 “March Classic” on March 21 in London, Ont.

Figure 2: Season long visual control (%) of lamb’s quarters with glyphosate in soybean when pre-emergence herbicides were used compared to when they were excluded in “Roundup Ready” soybean crop (adapted from Westhoven et al. 2008).

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

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