Correctly identifying the main grassweeds is the first step to effective control. ADAS' Sarah Cook profiles the main culprits and points out how to identify them.

Correct grassweed identification is vital to ensure the right strategies are employed to keep these pernicious weeds at bay.

They are especially damaging in winter cereals, where the opportunity for cultural control is often restricted due to drilling date and workload, and where spray choice is limited and usually needs careful targeting.

There is no room for error - almost all grassweeds are competitive, robbing the crop of nutrients and light.

There should be zero tolerance for all the major grassweeds in winter cereals except annual meadowgrass - if you can find them, you are losing yield.

They also affect quality, host ergot and take-all and can delay ripening and harvesting.

Others, notably wild oats and barren brome, can contaminate grain and, in bad infestations, lead to harvesting problems.

The best time to identify grassweeds is when they are heading, when the differences are most obvious.

But for effective autumn control correct identification of the seedling and young plant must also be made. Although some differences are still clear, more subtle variations need to be correctly distinguished.

Key pointers include growth habit, leaf shape and colour, presence or absence of auricles (hook-like projections that wrap around the stem at the end of the leaf sheath) and their size and shape, as well as characteristics of the ligule (an extension of the leaf sheath where it joins the leaf blade).

Blackgrass

Blackgrass ligule is tall and regular.

This is the main problem grassweed for arable growers. Although not the most widespread - its heartland is southern and eastern areas - it has spread rapidly to the north and west and has crossed the Scottish border.

Just 13 plants/sq m can cause a 5% yield loss in winter cereals. Good control is critical as each plant produces masses of seed, but increasing resistance is causing big problems in some areas.

Most seeds germinate from September to November. Young plants have twisted leaf blades with blunt tips; lower sheaths are often purple.

Stems are fine and sometimes reddish, leaves are fine, smooth and shiny with a pronounced groove. The ligule is long, flat and ragged. There are no auricles.

Italian ryegrass

Italian ryegrass has auricles that wrap around the stem.

This weed is mainly found in southern Britain and occurs mainly where grass features, or has featured, in the rotation.

Just 9 plants/sq m can cause a 5% yield loss. It is a prolific seeder and populations can increase rapidly, and resistance has been noted.

Leaves are dark green and hairless, glossy underneath, and finely pointed. Ligules are small - 1-2mm and blunt, while auricles are narrow.

Perennial ryegrass

Unlike its Italian cousin, perennial ryegrass is widely distributed across the UK.

It is also less aggressive, but established populations will cause similar yield losses in winter cereals. It tends to be found in rotations that include grass.

A key difference between it and most other grasses is that leaves of young plants are folded in the stem. The backs of leaves are shiny, while the smooth leaf sheaths may be bright red or pink. Auricles are small if present, and the ligule is short and blunt.

Bromes

Sterile brome has leaves which are hairy and twisted.

Sterile brome is widely spread across England, Wales and Scotland. It is most commonly found creeping in from field edges.

Severe infestations can cause crop lodging, and it can compete strongly in autumn, particularly under min-till regimes. Headland infestations average 7% yield loss, but this can more than double when the population spreads across a field. One plant can produce up to 2000 viable seeds in a season.

Leaves are covered in fine hairs and pointed. The ligule is long at 2-4mm, toothed and pointed.

Other problem bromes include meadow brome and rye brome. Both occur across southern England up to the Midlands and usually infest headlands.

Meadow brome leaves are moderately hairy and finely pointed. It has no auricles and a short to medium (1-4mm) jagged ligule.

Rye brome is rarer. It also has no auricles, but its ligule is short at 1-2mm. Leaves are long, pointed and twisted and somewhat hairy. Unlike the other two bromes, the stem is smooth rather than hairy.

Annual meadowgrass

Annual meadowgrass, a common grassweed, has a folded leaf.

This is the most common grassweed and is found in all arable areas. Although it has little effect on yield, it can hinder harvesting, harbour ergot and can be an important contaminant at harvest.

Unlike all the other key grasses mentioned, apart from perennial ryegrass, the leaf is folded in the stem, rather than rolled.

Leaves tend to be light green, have a curved tip and the undersides have a distinct central ridge. There are no auricles and the ligule is long (2-5mm) often roundly pointed and smooth. Several generations can occur in a season, so it is often flowering.

Wild oat

The true (spring) wild oat germinates mainly in the spring, though some seedlings can be found in the autumn.

Wild oat looks similar to cereals but leaves twist anti-clockwise.

Just 1/sq m can reduce winter cereal yields by up to 1t/ha. It can spread rapidly, increasing 14-fold year-on-year, and, once established, is difficult to eradicate as seeds can remain viable in the soil for up to 10 years.

Young wild oats are similar to other cereals but with one key difference - the leaves twist anticlockwise once the plant has 2-3 leaves. Leaf margins tend to be hairy towards the base, and leaves are broad, flat and blue-green. Auricles are absent, and the ligule is medium to long and slightly pointed.

The winter wild oat is much more localised, favouring heavy clay soils in East Anglia and the Midlands. Young plants are very similar to their spring cousins.

Know your grasses - what to look for

Name	Ligule	Auricles	Hairy	Leaf	Stem	Colour
Blackgrass	Long and slightly irregular	No	No	Narrow with pronounced groove. Sharply pointed	Sometimes purple	Mid green
Wild oat and Winter wild oat	Medium Ðlong,	No	Leaf edges	Broad with anticlockwise twist of leaves at	Smooth	Blue-green
	slightly pointed			2-3 leaves
Meadow brome	1-4mm, jagged	No	Yes	Flat, wide, finely pointed, twisted	Softly hairy	Dull green
Rye brome	1-2mm	No	Yes	Flat, wide, long, pointed twisted	Slightly hairy	Dull green
Sterile brome	2-4mm, toothed, pointed	No	Yes	Flat, twisted	Purple striped at base	Dull green
Italian ryegrass	1-2 mm, blunt	Yes	No	Glossy on reverse, finely pointed	Smooth	Dark green
Perennial ryegrass	Short, blunt	Yes	No	Folded and glossy on reverse	Smooth	Dark green
Annual meadowgrass	2-5mm, smooth	No	No	Folded, narrow, curved tip	Flat	Light green