Identifying grass weeds in cereal crops can be challenging, especially during the young growth stages, as opposed to spotting mature grass weeds when they flower or have seed heads visible. Keep this guide to help you identify those weeds in the field.

Annual meadow grass, sterile brome and spring wild oats

  • Common and widespread grass weeds in our tillage farms.
  • Early identification can give growers and advisers a head start in planning an effective spray programme and timing it correctly when susceptible populations are small, actively growing and at their most vulnerable growth stage.

    • Lesser canary grass, blackgrass and Italian ryegrass

  • Not present on all farms, but cases are rising.
  • Especially, with blackgrass and Italian ryegrass, early identification can help growers/advisers to take measures to stop the weed getting out of control (eg mapping affected areas, hand rogueing for small infestations or burn-off with glyphosate for large weeds), as the majority of these plant populations are resistant or suspected of being resistant to herbicides.

    • Identifying these weeds

    Young plants of these problem grass weeds can be differentiated based on vegetative structures, (see Figure 1).

    When examining weeds you may need to use a lens or magnifying glass to help see the plants better.

    You should examine the plants carefully at the leaf blade, ligule, collar and sheath for the following:

    (1) The presence or absence of hairs on the leaf blade and leaf sheath.

    (2) The shape and size of the ligule (little transparent membrane found at the junction of the sheath and blade).

    Identification keys for young grass weeds

    The pictures of young grass-weed plants and weed keys for each one can be seen in Figures 2 to 7.

    Sterile brome: Fig. 2

    Sterile brome plants develop broad and flat leaf blades. They can be identified by their very hairy leaf blades and sheaths, purple leaf sheath with a stripe effect and a ligule that is medium in size (2-4 mm) and serrated.

    Wild oats: Fig. 3

    Wild oat plants develop broad and flat leaf blades. They can be identified by their leaf blades twisted anti-clockwise, which is apparent even at the 2-4 leaf stage. Fine hairs can be seen along the edge of the leaf blade and sheath, and a ligule that is long (6-8 mm) and rounded.

    Lesser canary grass: Fig. 4

    Lesser canary grass plants develop broad and flat leaf blades. They can be identified by their hairless leaf blades, a distinct red sap on the root tip, and a medium to long (3-8 mm) and pointed ligule.

    Annual meadow grass: Fig. 5

    Annual meadow grass plants develop narrow or slightly flattened leaf blades. They can be identified by its bright green leaf blade and pale green underside sheath with boat shaped tip, hairless leaf blades, and a ligule that is medium (2-5 mm), roundly pointed and serrated.

    Italian ryegrass: Fig. 6

    Italian ryegrass plants develop narrow or slightly flattened leaf blades. They can be identified by its hairless leaf blades, dark green glossy leaves, red leaf sheath, and a short (1-2 mm) and blunt ligule.

    Blackgrass: Fig. 7

    Blackgrass plants develop narrow or slightly flattened leaf blades. They can be identified by their hairless leaf blades, purple leaf sheath (not all populations will have colouration) and a medium-sized (2-4 mm), blunt and serrated ligule.

    Are leaves rolled or flattened?

    The leaves of all grass weeds are rolled in the shoot, except for some species such as annual meadow grass, which has flattened leaves in the shoot. To determine this, you need to roll the plant back and forth between your fingers If it flips from one side to another, then it has flattened leaves, or if it rolls smoothly, then it is rolled. Alternatively, you can cross-section the stem to determine whether it is flattened or rolled, see Figure 8.

    In brief

    Walk your crop before spraying to identify grass weeds correctly and early, which will help you plan and take cost-effective control measures.

    Walk your crop after final spraying to examine the efficacy of herbicide control, and if needed, mark any problem patches or weed escapes.

    Taking action speaks louder than mere words. Fields that are identified with blackgrass and Italian ryegrass require a zero-tolerance approach, and drastic measures must be taken to control those weeds such as spraying areas of the crop with glyphosate.