Tillage farmers in the UK have been left with cultural control as being the primary means of tackling blackgrass infestations in crops.
The weed, which is now endemic in England, Scotland and Wales, first demonstrated herbicide resistance back in 1983.
ADAS weed scientist Dr. Sarah Cook took part in the most recent edition of the Tillage podcast.
She said: “Blackgrass comes up in the autumn. So, delayed drilling means that crops can be sown out after the main peak of emergence.
“We also know that the seed cannot emerge from depth. Ploughing the seed down will bury it so that it cannot emerge.
“Approximately 70% of blackgrass seeds disappear every year. They either die or rot in the ground,” she added.
“So ploughing one-year-in-three or one-year-in-four will ensure that the seed bank is reduced very significantly.”
UK research work has verified that steps taken to reduce seed return represent the most effective way of controlling blackgrass populations.
Cook further explained: “One of the most radical ways of controlling blackgrass is to let heavily infested crops grow out until May, just prior to the plants set their seeds. At that stage, it’s a case of killing off the entire field.
“This is one of the most effective ways of preventing herbicide resistant blackgrass from setting its seed.”
According to Cook, spraying a crop of with Roundup or making silage with it, are two options that can be considered in this context.
She added: “Sometimes growers will be left with no alternative but to take this approach. Herbicides tend to work better when they are dealing with lower populations of weeds.
“The subsequent crop can be direct drilled into what should be a relative clean seed bed.
“Disturbing the soil excessively is not recommended as this will only bring up blackgrass seeds that are located below the surface.”
Crop varieties to tackle blackgrass
The ADAS scientist confirmed that hybrid winter barley varieties are very competitive when sown out in fields containing significant blackgrass seed banks.
“Increasing seed rates will also help in the fight against blackgrass. The key to success is getting a new crop well established at an early stage,” she explained.
“By taking this approach, it will be as competitive as it can be in terms of fighting blackgrass.
“Proactive crop management of this nature will also allow the herbicides that are used to have a greater impact.
“Blackgrass is so easy to spread from field to field. Given this reality, a zero tolerance approach to the weed is the best way of getting to grips with it,” she concluded.