Grass weeds are a problem on almost all tillage farms in Ireland. Wild oats, bromes and annual meadow grass are the most common.
However, other weeds such as canary grass, Italian ryegrass and blackgrass are growing in terms of significance.
Even though cereal growers may be aware of the existence of these weeds, the scale of the associated problems and the means by which to control them are less well-known.
The critical first stage, is the task of identifying the various grass weeds.
According to Teagasc, blackgrass is now growing in every county in Ireland. While the majority of tillage farms do not have this problem, as of now, the challenge is one of keeping blackgrass out – and this takes vigilance.
Blackgrass
The specific threat posed by blackgrass was addressed by Dr. Louise Cooke, from ADAS, who spoke at the 2023 Teagasc Grass Weed Conference.
ADAS is the UK’s largest independent provider of agricultural and environmental consultancy, policy advice, and research and development.
Dr. Cooke said that, in the UK, cereal farmers are currently living with the challenge posed by the weed, but “really, the level of any weed infestation should be set at zero”.
“Where blackgrass is concerned, the presence of 100 heads per square metre can lead to a 13% reduction in grain yields. If the figure goes up to 500 heads, then yields can be reduced by 50%,” Cooke explained.
Tackling blackgrass and grass weeds
The ADAS representative went on to confirm that dealing with blackgrass comes down to a numbers game.
One blackgrass plant can produce 10 heads, each with a potential to produce up to 100 seeds, but “if the weed has plenty of room to grow in an uncompetitive crop, seed production rates will increase significantly”.
“Blackgrass seed viability averages 60%. So, even a moderate level of infestation can result in the production of one million seeds per hectare, with the potential to germinate.
“As a result, blackgrass populations can grow dramatically within two to three years. This assumes that no measures to control the problem are taken.”
Current research points to the role of integrated weed management in getting to grips with a blackgrass problem.
In practical terms, this means trying to control weeds without the use of chemicals. However, herbicides can be considered as a last resort option.
This only works if weed populations have been dramatically reduced by other means at this stage.
Critical within this approach is an understanding of the biology associated with the weed being targeted.