Photo Credit: Author

By Kaeley Kindrachuk, B.App.Sc., TechAg, Crops Extension Specialist, Outlook

Green foxtail is a widespread weed across the prairies and producers have been trying to control it for decades. Green foxtail has consistently ranked in the top three in the Agriculture and Agri-Food Canada (AAFC) weed surveys since the 1970’s. It is not a difficult weed to control, but because herbicide resistance is on the rise, it is becoming increasingly important to know more about this weed and the tools available to control it.

The conditions required for green foxtail to germinate can vary:

  • Temperature – Green foxtail germinates later in the spring, with peak germination occurring once temperatures have hit 20 C to 30 C. Since it emerges later, this usually means that these weeds may be missed by pre or post emergent herbicide applications. Germination rates will decrease if temperatures are lower (15 C to 25 C), but it will still occur.
  • Seed depth – The optimal depth for green foxtail seeds to germinate is at 1.5 to 2.5 cm. If seeds are buried below 12 cm, there will not be any germination.
  • Longevity – Green foxtail is viable in the soil for up to 33 months, but in optimal conditions can remain viable for up to three years.

Considerations for control with herbicides:

  • Timing – Controlling green foxtail early is ideal, while the weed is at the one to three leaf stage, in order to minimize yield reductions. Early emerging weeds are most competitive. Late emerging weeds do not have as much of an effect on yield; however, they still produce seeds that enter the weed seed bank. Herbicide control options are limited in fields where the green foxtail is resistant to groups 1 and 2 herbicides. Consult the Guide to Crop Protection to see all available options with correct crop staging.
  • Herbicide resistance – In the last AAFC weed survey in 2014-15, 400 fields were surveyed. Of the 104 fields where green foxtail was found, 31 per cent of them had an herbicide resistant weed population. Group 1 resistant green foxtail was found in 17 per cent of the fields and group 2 resistant green foxtail was found in 15 per cent of the fields. Two fields had group 1 and 2 resistant green foxtail. The next weed survey is underway and will be wrapped up in 2021.
  • Plant characteristics – The ligule of green foxtail is a fringe of hair (Photo 2), and the bristly spike-like panicle resembles a bottle brush. One of the common ways to distinguish green foxtail from yellow foxtail is that yellow foxtail has long spindly hairs at the leaf collar.

Green foxtail can also be a host for viral diseases, such as Wheat Streak Mosaic Virus. When seeds are mature in late summer or early fall, they will drop from the panicle to the soil surface. Larger plants can produce 5000-12000 seeds per plant under optimum conditions, but these weeds commonly produce hundreds of seeds per plant. Seeds are also spread by birds and water and can float on water for up to 10 days.

For more information, contact your local regional crops extension specialist or call the Agriculture Knowledge Centre at 1-866-457-2377.

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