The key to controlling a grass weed problem is identification, according to Teagasc’s Ciaran Collins. This is important as farmers need to know what weed they are targeting.

Speaking at the recent Teagasc Crops and Cultivation event, Collins emphasised the importance of knowing weed biology for grass weed management.

Different weeds require very different control strategies, he said. Spring-germinating weeds pose different problems to winter-germinating species.

“Stubble cultivation techniques are very effective for weeds that germinate in the autumn, such as sterile brome and black grass.

“For lesser canary grass and wild oats, they will require a different approach because they are spring-germinating weeds,” Collins explained.


Ronan Byrne, a Teagasc Walsh Fellow at Oak Park, discussed the key traits for identifying grass weeds.

“Early identification is the first and most important step in grass weed control,” Byrne began.

There are a number of key characteristics to pick out and distinguish one grass weed from another.

Auricles are collar structures that wrap around the stem, down at the base of the leaf sheath, Byrne explained. He added: “You can see them in barley and wheat, but not in wild oats.”

common grass weeds

From L-R: Wild oats, wheat and barley auricles. Image source: Teagasc

Spring-germinating grass weeds

Lesser canary grass

Lesser canary grass can remain dormant in the soil for extended periods, Byrne said.

Lesser canary grass characteristics:
  • Leaves are pale, broad and very soft to touch;
  • Red sap at the end of the root tips – classic characteristic;
  • No auricles;
  • Tufted seed spike – quite distinctive out over the crop canopy;
  • Small, plump, dark brown seeds inside of the spike.
identify common grass weeds

Canary grass in spring wheat. Image source: Teagasc

common grass weeds

Vegetative canary grass and seed head. Image source: Teagasc

Wild oats

Byrne gave farmers an update on the wild oats situation on Irish farms.

Part of Byrne’s area of study involves understanding the issue of herbicide resistance in grass weeds, including resistance in wild oats.

“Last summer, we collected samples from 76 sites across Ireland and tested them for resistance to a number of different herbicide active ingredients,” the Teagasc Walsh Fellow said.

The herbicides were split into two main crops. These were graminicides and sulfonylureas. The big finding from our research so far is that we do have resistant wild oats in the country.

“This is something we may not have thought was an issue this time last year, but we do have an issue now and it’s going to be more of a problem in continuous spring barley ground,” he said.

Wild Oats characteristics:
  • Tall, sturdy and robust grass;
  • Hairy stems and leaf margins;
  • No auricles;
  • Loose panicle structure;
  • Dark-coloured, hairy seeds with black, bent awns.
common grass weeds

Wild oats in barley crop. Image source: Teagasc

common grass weeds

Wild oats panicle and hairy seeds. Image source: Teagasc

Winter-germinating grass weeds

Sterile brome

Sterile brome is one of the most common grass weeds we have here in Ireland, Byrne said.

Sterile brome characteristics:
  • Hairy stems;
  • Vertical, pale red striping at the base of the stem – very good for early identification;
  • Loose, drooping panicle structure;
  • Seeds have long awns, arranged in a wedge-shaped spikelet;
  • Deep-purple colour;
  • Prostrate growth (along the ground).
common grass weeds

Sterile brome panicle. Image source: Teagasc

Soft brome

Byrne mentioned that Oak Park is seeing a lot more soft brome this season in particular. “You can distinguish soft brome from sterile brome when it heads out,” the Teagasc Walsh Fellow said.

Soft brome characteristics: 
  • Seeds tightly arranged in an oval-shaped spikelet;
  • Very short hairs on the spikelet – classic characteristic;
  • Upright growth;
  • Compact panicle with short branches.
common grass weeds

Soft brome. Image source: Teagasc

Black grass

When discussing black grass, Byrne said: “If you are seeing heads of black grass in your crop, it’s already too late to do anything about it. It’s already next year’s problem.” Hence, why early identification is key.

Characteristics of black grass – young:
  • Purpling at the base of the stem;
  • Long, slender, dark-green leaves;
  • No auricles;
  • Massive tillering capacity.
identify common grass weeds

Early tillering black grass. Image source: Teagasc

Characteristics of black grass – mature:
  • Slender, cylindrical long spikelets;
  • Heads range in colour from deep purple to green;
  • Very upright growth.

“You have to treat black grass with zero tolerance and have a long-term, sustainable, integrated weed management strategy in place,” Byrne concluded.

identify common grass weeds

Black grass flowering head. Image source: Teagasc