Grassy weeds in winter wheat at harvest

OMAFRA Field Crop Report for July 28

The seed head of chess grass extending beyond a winter wheat canopy.

Three different types of grassy weeds have been found above the winter wheat canopy at harvest this year. To prevent them from becoming a problem, they need to be identified so that the appropriate management actions can be taken. Here is a breakdown of each grass species and control options.

Chess grass (Bromus secalinus)

Management: Chess grass is a winter annual species that emerges primarily in the fall and will affect fall planted crops the most. Spring tillage or burndown herbicides will control seedlings. Therefore, it is usually not an issue in corn, soybeans or dry beans. It is important to make note of fields which have this weed, so that the next time it is planted to winter cereals, it can be controlled in the fall or early spring with herbicides that are effective.

Herbicide options in winter wheat:

After crop emergence (Fall): Simplicity GoDRI
After crop emergence (Spring): Simplicity GoDRI

Annual/Italian ryegrass (Lolium multiflorum)

Although ryegrass can certainly be a valuable forage grass for livestock production, it is a difficult to control weed in other crops. Ryegrass can express as an annual, biennial or perennial. In the United States, populations that are resistant to groups 1, 2, 9, 10 and 15 have been documented. This presents several challenges for successful control.

Management: The U.S. based “take action” initiative has a very good resource on management of Italian ryegrass at iwilltakeaction.com/weed/italian-ryegrass. Research by Dr. Peter Sikkema and Dr. Darren Robinson (University of Guelph, Ridgetown) on spring control ahead of soybeans and corn has demonstrated that:

  1. Air temperatures affect herbicide performance and applications should be made when there is a good stretch of temperatures above 10 C.
  2. Ryegrass is more sensitive to herbicides when it is smaller than 30 cm (12”) in height.
  3. A rate of glyphosate 540 g/L at 1.87 L/acre should be used. Tank-mixing this rate of glyphosate with Assure II (quizalofop-p-ethyl) ahead of soybeans or Steadfast (nicosulfuron/rimsulfuron) ahead of corn will improve control.

If you see ryegrass in your cereal stubble, it would be worthwhile to spot spray plants with a 2 per cent glyphosate solution to see if they will die. If they survive, contact either [email protected] or [email protected] so that resistance testing can be pursued.

Bluegrass (Poa spp: Annual, Rough-stalk, Canada)

Bluegrass species are becoming more common in field crops. Three species are consistently being found in field crops: annual bluegrass, roughstalk bluegrass and Canada bluegrass. The latter two being perennial species.

Management: Glyphosate (540 g/L) at 1.34 L/acre typically does a good job of killing emerged plants, but new seedlings will emerge later. The inclusion of soil-applied herbicides is a useful tactic to reduce later-emerging seedlings and seed dispersal. Ontario research has demonstrated that the soil-applied active ingredient called “pyroxasulfone” (found in Fierce EZ, Focus, Zidua SC) does the best job at preventing seedling emergence.

A post-harvest application of glyphosate + Zidua SC has been effective at providing control of annual bluegrass into the next season. This fall application timing coincides with peak germination of winter annual biotypes. Zidua SC has also proven to be effective when applied in the spring. Trifluralin (e.g. Treflan, Rival) is the only other herbicide available in Eastern Canada that lists annual bluegrass on its label as being controlled. It can be used in soybean, dry bean and canola.

In winter wheat, spring applications of either Simplicity GoDRI, Axial or Varro to bluegrass that was 10 cm tall or less, provided excellent control of roughstalk bluegrass in a 2021 Ontario trial.

Click here to read the full July 28 report on the Field Crop News website.

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