Growers must target a minimum of 97% Blackgrass control in autumn-sown oilseed rape crops simply to maintain the status quo. Anything less will result in increasing Blackgrass populations, leaving subsequent cereal crops increasingly vulnerable to yield losses.
Research has shown that below 97% control, Blackgrass has the potential to spread and increase in individual plant numbers. With 80% of Blackgrass plants germinating and emerging during the autumn, the months of September and October are therefore critical for implementing an effective Blackgrass reduction strategy.
“The timeline for establishing oilseed rape doesn’t allow enough time to undertake many of the cultural techniques that are used to combat Blackgrass in cereals, so it is essential to make the correct chemistry choices and to apply those chemicals at the optimal time,” advises Gemma Sparrow, oilseed rape herbicide specialist for Adama.
“Oilseed rape growers must approach Blackgrass control in the same structured, detailed and integrated manner as the weed is managed in cereal crops. Cultivation technique, Resistance Status, drilling date and existing weed pressure will all affect the Black-grass strategy, but the best advice is to go early and to stack actives using the best, non-resistant products for the job.
“A sequenced approach of an early (pre-emergence to 4 true leaves) application of Crawler (600 g/kg carbetamide), followed by propyzamide in November if/when a second flush of grass weeds has emerged will give oilseed rape growers the best chance of keeping ahead of Black-grass populations. Where blackgrass pressure is extremely high, a non-resistant graminicide should also be considered between the Crawler and propyzamide treatments.”
Applying Crawler early in the season has the added advantage of reducing the risk of chemical losses by avoiding heavy rainfall events which increase with incidence and cause greater levels of leaching from the end of October.
Whilst any early Blackgrass control policy will add extra cost to typical oilseed programmes, it is a small price to pay to safeguard the yield potential of both the oilseed rape crop and subsequent cereal crops. And with no known cases of resistance to carbetamide in Blackgrass, it is a given that products such as Crawler will provide a beneficial effect.
“Crawler kick starts the Blackgrass control by targeting the roots of young plants and weakening their resolve to subsequent chemistries. It is also effective against Chickweed and Speedwell, with ryegrasses, meadow grasses and wild oats also showing moderate susceptibility.”