Crop Report – Grassy weeds in winter wheat

Figure 2. The “spike” seed head with distinctive short awns of annual/Italian ryegrass poking through a winter wheat canopy.

What was that grassy weed in my winter wheat at harvest time?

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 (Bromus secalinus):

Figure 1. The seed head of chess grass that extends beyond the winter wheat canopy. 
Figure 1. The seed head of chess grass that extends beyond the winter wheat canopy.

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):

Figure 2. The “spike” seed head with distinctive short awns of annual/Italian ryegrass poking through a winter wheat canopy.
Figure 2. The “spike” seed head with distinctive short awns of annual/Italian ryegrass poking through a winter wheat canopy.

  

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% glyphosate solution to see if they will die. If they survive, contact either mike.cowbrough@ontario.ca or ftardif@uoguelph.ca so that resistance testing can be pursued.

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

Figure 3. A dense stand of bluegrass competing with winter wheat.
Figure 3. A dense stand of bluegrass competing with winter wheat.
Figure 4. A close-up of the open panicle of roughstalk bluegrass.
Figure 4. A close-up of the open panicle of roughstalk bluegrass.

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.

Weather Data

Location 

Year

Weekly July 19 – July 25Accumulated
Highest Temp (°C)Lowest Temp (°C)Rain (mm)Rain (mm) April 1stGDD 0C April 1st GDD 5C April 1stCHU May 1st
Harrow2021311149373191013481924
202031164284182212731929
2019341312360174511931733
Ridgetown20213095353179912461812
202029146249172911951814
2019341026346165511051637
London2021301120283178712401785
2020301511227167211411727
2019331247402156410391568
Brantford2021291014265176612161756
2020301613187168011541710
20193412274161910821626
Welland202127128274176112081762
2020291611255171511821799
201933138315168411311703
Elora2021281049241162710861621
2020281316222154610391604
201934312527791225
Mount Forest202127934286162710901629
2020271231305152710331614
201931912914589391482
Peterborough20212998271162610751608
202030138163155310421603
2019349031414889551459
Kingston2021271411201166811161658
2020291511222167311351759
2019321214315162410751635
Kemptville2021291317229175712001713
2020321310159164611191693
2019331020315239961502
Earlton20212884739515129801455
20203011227813629181471
2019318330912157571244
Sudbury2021311037284154710161516
20202812833214269561530
2019319030112217691247
Thunder Bay2021315422913988801367
2020268614112748311355
2019299423511246731126
Fort Frances202132101217014879631501
20203261120014169401501
201929101925912527721264
Report compiled by OMAFRA using Environment Canada data. Data quality is verified but accuracy is not guaranteed. Report supplied for general information purposes only. An expanded report is available at www.fieldcropnews.com.

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