06 June 2025

Identifying critical tillage grass weeds

Some growers have spotted blackgrass for the first time on their farms in recent weeks and have sought help to confirm its identification. Correct identification is crucial, says Vijaya Bhaskar, Research Officer.

We have received reports of an increasing presence of blackgrass, Italian ryegrass, and bromes in tillage crops this season. Unlike last season, annual meadow grass is now present only on a few farms that have relied solely on broad-spectrum spring herbicides.

These critical grass weeds can produce large numbers of seeds that will reinfest your land if no action is taken. Control measures include marking weed patches, preventing seed return through hand rogueing or spot spraying, and, for severe infestations, whole cropping or spraying off. Delaying these measures until after seed set will lead to costly, long-term consequences.

Mature grass weeds are easier to spot when they are flowering or have visible seed heads.

Pictures to help with accurate identification

Italian ryegrass in wheat: An increasing threat, with 81% of suspected populations confirmed resistant, necessitating zero-tolerance and strict biosecurity. The plant has flattened spike heads with awned spikelets on opposite sides of the stem. In April, Teagasc confirmed Ireland’s first glyphosate-resistant Italian ryegrass population, raising serious concerns.

Blackgrass in wheat: Not present in every farm but cases are rising. Resistance confirmed in 63% of suspected populations, necessitating a zero-tolerance and strict biosecurity. The plant has compact, slender spike heads with brown or purple-tinged awned spikelets.

Spring wild oats in barley: A common, competitive grass weed with loose panicle, large spikelets and bent awns. Resistance confirmed in 34% of suspected populations. Hand-rogue herbicide escapees to prevent resistance development.

Sterile brome in barley: A common, competitive grass weed with open panicle branches that droop or nod to one side, and a hairless or only minutely hairy main panicle axis. No resistance detected to full rates of ACCase (eg. Falcon) / ALS (eg. Pacifica) herbicides, but widespread tolerance to reduced rates has been well documented.

Annual meadow grass in wheat: A common low-priority grass weed with branched flowering heads and awnless spikelets. Over-reliance on spring herbicides in winter wheat, instead of pre-emergence or autumn residual herbicides, has contributed to unintentional resistance, with 14 of 16 suspected populations confirmed ALS-Pacifica resistant.

Great brome in barley: Populations are increasing (based on annual sample submissions), with no resistance detected to full rates of ACCase (eg. Falcon) / ALS (eg. Pacifica) herbicides, but tolerance to reduced rates is noted. The plant has open, spreading panicle branches with a hairy main axis.

Soft brome in barley: Populations are increasing (based on annual sample submissions). No resistance detected to full rates of ACCase (eg. Falcon) / ALS (eg. Pacifica) herbicides, but tolerance to reduced rates is noted. The plant has compact heads, hairy spikelets with tightly packed seeds, and saucer-shaped mature seed cross-sections.

Lesser canary grass in barley: It has long, dense spike heads and a distinct red sap at the root tip. Although control is usually not listed on ACCase or ALS herbicide product labels, glasshouse trials show these herbicides are effective at full rates on small, actively growing plants.

Close-up views of seed heads

Wild oats (loose panicle), lesser canary grass (dense), blackgrass (slender) and Italian ryegrass (flattened)

Sterile (open, drooping), great (open, spreading) and soft (compact) brome types.