Weed of the Week: green foxtail

Call it what you will — bottle grass, green bristlegrass, green millet, pigeon grass, wild millet or, as it best known in Western Canada, green foxtail — the weed is becoming a growing problem for prairie farmers.

Less tillage has had many positive effects on agriculture, but it has also resulted in more weeds.

One benefactor has been green foxtail, formally known as setaria viridis.

This weedy millet is well known across North America and is registered as a noxious weed in Canada and 46 American states.

Ten years ago, it was considered to be present in more than half of the fields in Western Canada’s black soil zone and in one-quarter to one-third of the brown zone and southern parts of the black zone.

Researchers say green foxtail is likely as prevalent in the southern Prairies now as it was in traditional canola country 10 years ago.

Green foxtail is an annual with a fibrous root system that can take advantage of scant resources. Reproducing from seed, the plant generates 350 to 500 seeds per head with as many as 10 heads per plant.

As a result, it can spread quickly from a single plant if allowed to mature.

Green foxtail is a slow germinator, preferring to start life in soil with abundant moisture that is 15 to 35 C. It has trouble competing with dense crops because of its need for light and heat.

It will develop slowly in dry conditions, making them good targets for chemical control.

Seeds tend to germinate and generate viable plants from soil depths of 10 to 25 mm, so harrowing fields can generate germination in the spring by creating warmer soil and placing the seeds in a desirable seed bed.

Foxtail first appears on the soil’s surface as a single, tiny, green leaf running parallel to the ground. Still tiny at the four leaf stage, it can be confused with other cereals.

The little fibres that appear where the leaf meets the stem before heading are tell-tale signs. Once mature, the head’s bristly, spiky panicle is a dead giveaway.

The weed is a poor crop competitor in cooler conditions, as long as the crop gets an early start. However, wider row spacing can allow it to get a root-hold in a field.

Dense, tall crops that canopy well, such as canola, durum and barley, can win out over the weed.

However, pulse crops such as a lentils, flax and shorter spring cereals, can lose the race with green foxtail unless they are dense.

Winter wheat and fall rye are good choices for fields with green foxtail problems. The weed’s rapid growth cycle can be problematic for cultural control practices when it emerges with the crop.

Forage rotations of three years or more are useful control methods but unrealistic for many grain operations.

Chemical control is possible with most crops, but oats has only one registered solution for suppression: linuron with MCPA ammine. This works with other cereals as well.

Ten products are available in barley, including pinoxaden, Axial, tralkoxydim (available in a mix with bromoxynil and MCPA as Achieve Liquid Gold or for application with an adjuvant under Liquid achieve, Bison or Marengo), fenoxaprop (under a variety of names including Puma), triallate and trifluralin (Fortress), Trifluralin (Treflan, Rival and Fortress) and pyrosulfatole mixed with fenoxaprop and bromoxynil (Tundra).

Most of the barley choices are registered for wheat, as well as clodinafop (under a variety of names including Horizon and various mixes such as Harmony) and flucarbazone (Everest or Sierra). Suppression is available with pyroxsulam (Simplicity) and thiencarbazone (Varro).

Clearfield wheat offers those control choices.

Most products that control cereals in broadleaf crops are effective.

Green foxtail can germinate late in the season and still reach maturity and produce viable seed, so pre or post harvest applications of glyphosate or similar products can help control it.