Weed of the Week: foxtail barley

Some weeds have flourished with the increase in no-till acres over the past 20 years. One of them is foxtail barley, known to biologists as hordeum jubatum.

It has become an increasing concern after our series of wetter years and with the expansion of saline-affected soils.

Foxtail barley tolerates the saline conditions that occur once it dries out after periods of excess moisture. It has managed to establish itself on a significant number of acres in Western Canada recently.

The nasty pest thrives when tillage is reduced, as has been the case over a large number of acres when it was too wet to seed or work. There are very few herbicide control options and those that are available are crop or timing specific.

Foxtail barley has a shallow, fibrous root system that makes it very susceptible to control through tillage. However, as we moved away from steel in soil, this weed has continued to flourish since more normal weather patterns have returned to the region.

There are three chemical timings for control of this problem.

The first window is the pre-seeding opportunity.

Work done at the University of Saskatchewan shows that a .5 litre per acre rate of glyphosate using formulations with 360 grams of active ingredient per litre and applied at approximately the 120 growing degree days point gave acceptable control of seedlings, those with crowns less than one inch in diameter. Established plants were suppressed but survived the treatment.

It has been observed that even rates as high as 1.5 litres per acre will not control all established plants in all years. Control of both seedling and established plants was increased if the application was delayed until 240 growing degree days.

Late applications of 1.25 litres provided good control of established plants in some years.

This moves us to the second window of control — in-crop herbicides.

We are quite limited with options for in-crop control, especially in cereals.

Quizalofop (Assure II, Yuma GL) provides quite good control in broadleaf crops, followed by clethodim (Select, Centurion, others) and sethoxydim (Poast Ultra).

While not registered, many farmers will tank mix quizalofop with glufosinate or glyphosate for their early spray application.

Spraying the outside 60 to 90 metres around sloughs is usually sufficient to control an early infestation.

Control is very limited in cereals. Everest shows suppression of foxtail barley in American literature. In some Canadian studies it has provided control of emerging seedlings, but has limited effect on overwintered plants.

The best opportunity for control is September and October, and success depends on fall rains that stimulate foxtail barley regrowth.

Glyphosate at one litre per acre applied pre-harvest or post-harvest can be expected to provide greater than 80 percent control of established plants, if plants are actively growing.

However, the larger the plant the poorer the control. The rate should be increased to 1.5 to two litres if the foxtail barley plants have celebrated two birthdays.

The addition of quizalofop to the glyphosate will also improve control.

Pre-harvest applications are most effective when significant moisture had occurred in August.

The extremely hairy, narrow leaves mean it is important to use adequate water volumes and recommended rates of surfactants with whatever herbicide you choose.

Foxtail barley doesn’t establish to be a problem in one year, and it will probably take more than a single season to get it under control.

Control methods

  • Foxtail barley is a tough-to-control perennial weed, especially in zero tillage systems.
  • Glyphosate can effectively control seedlings at relatively low rates if properly timed.
  • Higher rates of glyphosate are required for control of mature or overwintered plants.
  • For pulses and oilseeds, research has shown that Assure II can be used for in-crop suppression foxtail barley.
  • Limited control options in cereals make it important to emphasize pre-seeding and post harvest control options.
  • High seeding rates and proper placement of nitrogen fertilizer help to reduce yield losses and slow the spread of foxtail barley.
  • Use of cultivation for control of foxtail barley might be the best option available, especially if populations are limited to field margins or areas around sloughs.

Thom Weir is an agronomist with Farmer’s Edge. He can be reached by emailing thom.weir@farmersedge.ca.

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