Blackgrass

Blackgrass (Alopecurus myosuroides) is an annual weed that can reach heights of 80-90cm. The stems are round and slender with few nodes. The leaves are hairless with no auricles and the ligule is long, blunt and finely serrated. The flowering head is a compact spike 3-6cm long, narrow and pointed, often with a purple tinge. Spikelets are single flowered with prominent awns.

Blackgrass is a major problem to UK farmers. As an individual plant it is not as competitive as wild oats, but because populations of 200-400 plants per square metre are quite common, yield penalties are severe. It has been calculated that just 12 plants/m2 can reduce yield by 5%. Seed is shed before harvest thereby replenishing the soil seedbed.

Increasing prevalence of grassweeds in cereals can be attributed to a shift in farming practice including:

• Movement towards more profitable autumn cropping
• The use of minimum cultivation systems
• A trend towards earlier drilling
• A reduction in rotations and spring cropping
• The straw burning ban

Biology

Blackgrass is particularly problematic on heavy soils or where drainage is poor and soils are wet. The major blackgrass regions are on the eastern side of the country which has traditionally been the cereal growing area of the UK.

The blackgrass life cycle favours winter cereals grown in a minimal cultivation system. 80% of seeds germinate in the autumn peaking in September-October. Seed dormancy is more prolific if the season is cool and wet. Blackgrass flowers in May-August, and seed is shed over 8 weeks, normally all before harvest. Each head can have up to 200 seeds, which can remain viable for 7-9 years in the soil.