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 25 Accumulated
Highest Temp (°C) Lowest Temp (°C) Rain (mm) Rain (mm) April 1st GDD 0C April 1st  GDD 5C April 1st CHU May 1st
Harrow 2021 31 11 49 373 1910 1348 1924
2020 31 16 4 284 1822 1273 1929
2019 34 13 12 360 1745 1193 1733
Ridgetown 2021 30 9 5 353 1799 1246 1812
2020 29 14 6 249 1729 1195 1814
2019 34 10 26 346 1655 1105 1637
London 2021 30 11 20 283 1787 1240 1785
2020 30 15 11 227 1672 1141 1727
2019 33 12 47 402 1564 1039 1568
Brantford 2021 29 10 14 265 1766 1216 1756
2020 30 16 13 187 1680 1154 1710
2019 34 12 274 1619 1082 1626
Welland 2021 27 12 8 274 1761 1208 1762
2020 29 16 11 255 1715 1182 1799
2019 33 13 8 315 1684 1131 1703
Elora 2021 28 10 49 241 1627 1086 1621
2020 28 13 16 222 1546 1039 1604
2019 343 1252 779 1225
Mount Forest 2021 27 9 34 286 1627 1090 1629
2020 27 12 31 305 1527 1033 1614
2019 31 9 129 1458 939 1482
Peterborough 2021 29 9 8 271 1626 1075 1608
2020 30 13 8 163 1553 1042 1603
2019 34 9 0 314 1488 955 1459
Kingston 2021 27 14 11 201 1668 1116 1658
2020 29 15 11 222 1673 1135 1759
2019 32 12 14 315 1624 1075 1635
Kemptville 2021 29 13 17 229 1757 1200 1713
2020 32 13 10 159 1646 1119 1693
2019 33 10 203 1523 996 1502
Earlton 2021 28 8 47 395 1512 980 1455
2020 30 11 2 278 1362 918 1471
2019 31 8 3 309 1215 757 1244
Sudbury 2021 31 10 37 284 1547 1016 1516
2020 28 12 8 332 1426 956 1530
2019 31 9 0 301 1221 769 1247
Thunder Bay 2021 31 5 4 229 1398 880 1367
2020 26 8 6 141 1274 831 1355
2019 29 9 4 235 1124 673 1126
Fort Frances 2021 32 10 12 170 1487 963 1501
2020 32 6 11 200 1416 940 1501
2019 29 10 19 259 1252 772 1264
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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