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The Scourge of the South

Jun 8, 2017

By: Thom Weir, Senior Precision Agronomist, Farmers Edge

Over the next couple of blogs, I would like to discuss two weeds. One I will refer to as “The Scourge of the South” and the other as “The Scourge of the North.” Unluckily, I have worked in an area where the two come together so I have experience with both.

“The Scourge of the South” is Kochia. This weed was described in a column written by Michael Raine for The Western Producer, June 11th, 2015 edition. Since then, there have been a few updates that should be noted. As described in the article, Kochia is notorious for its seed production (up to 15,000 seeds per plant), it’s seed disbursement through tumbling in the wind, its ability to shed off spray droplets with its fuzzy leaves and its ability to become resistant to various herbicide groups. The latter is because, in part, to Kochia’s preference to outcross and in part due to the tremendous genetic variability species.

I have called Kochia “The Scourge of the South” because that is where it has established itself as one of the most significant weed problems.  Kochia is a “C4” photosynthetic pathway plant. Plants with this characteristic grow more efficiently in hot, dry weather, can convert low CO2 levels to sugars more efficiently and can store CO2 at night to use through the day. Other examples of C4 plants are corn, millets, foxtails, barnyard grass, pigweeds, & lamb’s-quarters.

Kochia also can survive in soils with moderate to high levels of salinity. Over the last few “wet” years, saline areas have expanded across western Canada and the northern prairie States in the U.S. With this expansion of saline soils, Kochia has also expanded.

Now to the real issue. Because of Kochia’s ability to outcross and its genetic variability, it has shown that it can become resistant to many of the herbicide groups we have relied on for its control. To date, Kochia resistance has been documented to Gr. 2 (ALS Inhibitors including Imidazolinones, Sulfonylureas, Sulfonanilides and others; Gr. 4 (2,4-D, dicamba and fluroxypyr); Gr. 5; Gr. 6 (Triazines); and Gr. 9 (glyphosate).  Even more disturbing is the fact that these resistance groups are being stacked. There are populations of Kochia resistant to Groups 2 and 9, 2 and 4 and recently a population in Kansas has shown resistance to Groups 2, 4, 5 and 9.

This spring, please be vigilant of Kochia. Review fact sheets on this weed and use cultural control methods along with chemical control. And when you use chemical control, use multi-action tank mixes and spray these at an early weed stage, to try and slow down at least, the spread of the resistant biotypes. And remember, as frustrating as it is, there is no way of visually identifying a multiple resistant Kochia from one that is susceptible to all groups of herbicides. It may be impossible to prevent multiple resistant Kochia blow in from a neighbour but we must all do our part to try and slow down the spread.

Adapted from: Leeson, J. Y., A. G. Thomas and C. A. Brenzil. 2003. Saskatchewan weed survey of cereal, oilseed and pulse crops in 1995 and 2003.  Weed Survey Series Publication 03-1.  Agriculture and Agri-Food Canada, Saskatoon Research Centre, Saskatoon, Saskatchewan.