Crop Report – Grassy weeds in winter wheat

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.

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.

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:

Air temperatures affect herbicide performance and applications should be made when there is a good stretch of temperatures above 10 C.
Ryegrass is more sensitive to herbicides when it is smaller than 30 cm (12”) in height.
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 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
Location	Year	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.