Teagasc tillage advisors have confirmed the presence of blackgrass infestations in a number of Irish cereal crops.
The weeds are now at flowering stage, with seed set to follow in a matter of days.
Getting on top of difficult grass weeds including bromes, canary grass and blackgrass, will now be a key issue for Irish tillage farmers.
However, this challenge has to be faced with a fast decreasing array of herbicides in the tool box.
It is essential that farmers are very aware of the life cycle and plant physiology of these weeds and it will be critically important as cereal growers strive to ‘work with nature’ when it comes to controlling them.
Teagasc agricultural advisor, Jimmy Staples, said:
“Effective management of blackgrass will require farmers to secure a 97% control rate every year.
“Each plant produces up to 10 heads. In turn, these can produce up to six million seeds/ha on the basis of just one blackgrass plant per square metre.”
He said that preventing seed return is one of the key objectives when it comes to controlling blackgrass.
“Where there is a low level of infestation, rouging the weeds is probably the best option. And crops need to be walked on a weekly basis over the next month or so.
“This will ensure that late-germinating blackgrass plants are identified,” Staple added.
According to the Teagasc advisor, growers can utilise a number of control options, in cases of high-blackgrass-infestation levels.
These include the use of whole cropping, mowing and baling, or crop destruction.
“Crop destruction refers to the use of roundup to completely clear out areas within a crop where high levels of blackgrass infestation exist,” Staples said.
“All control options must be taken before blackgrass sheds its seed. This takes place from mid-June onwards.
“So now is the best time for growers to take whatever control options are necessary.”
But some farmers will also want to know whether there is an option of planting infected fields out in grass.
According to the Agricultural and Horticultural Development Board (AHDB), average blackgrass seed decline in the soil is about 75% per year.
Seed persistence data and farm experience both support the view that a one-year fallow or grass ley is not long enough to reduce high blackgrass infestations to acceptable levels. After two years, less than 10% of seeds are likely to remain.
However, this could still be a large number and a longer break may be required.
Therefore failure to prevent seed return greatly undermines the value of a fallow or grass ley break.
The cultivation strategy at the end of any fallow or grass ley break is important.
Sufficient time needs to elapse between cultivating and sowing the next crop to allow the destruction of blackgrass seedlings emerging from residual seeds.