With the current season, one of the worst ever for blackgrass infestations, growers should be planning to take advantage of every option available to bring this and other grassweeds under control in autumn 2014, says Dow AgroSciences Stuart Jackson.
Harvest 2013 saw above average blackgrass populations after appalling winter conditions. However, early drilling into dry conditions in autumn 2013 saw herbicides run out of steam, whilst later sown crops did not receive full herbicide programmes.
“The result of two exceptional seasons is a very heavy burden of blackgrass and other pernicious grassweeds such as bromes, wild oats and ryegrass,” says Mr Jackson. “There will undoubtedly be some increase in resistant populations, but many fields can still be effectively cleaned up provided farmers draw up a detailed campaign.”
For some the campaign began pre-harvest with the worst infested fields being burnt off with glyphosate or whole crop silage being taken.
“For best effect, such action needs to be taken before the blackgrass seeds begin to fill,” says Mr Jackson.
At harvest, straw removal may help reduce the burden of seeds returned to the soil. Then the key is to make optimum use of stale seedbeds where winter wheat is going in again. This is best achieved with very shallow cultivation to encourage germination followed by a glyphosate application. Where conditions permit, this can be repeated two or even three times.
“It is understandable that growers want to crack on with drilling, especially on heavier land. However, not every field can be drilled on the same day, so identify the weediest fields and leave them to last in the sowing programme,” says Mr Jackson.
Rotation can also play a part. For instance, taking badly infested fields into winter oilseed rape where propyzamide products such as Kerb Flo 500 or AstroKerb can be used and will give a better level of control. And, consider spring cropping as well.
“Turn the new three crop rule to your advantage,” says Mr Jackson. “A spring crop will allow grass weeds to germinate throughout the winter, but be sure to use a stale seedbed before drilling as the options for grassweed control in spring cereals are far more limited.”
Cultivations are also important and there is evidence that the plough has a part to play in tackling grassweeds.
“For ploughing to be effective, it has to be well done. This means ploughs set to fully invert and skims set to put all the trash at the bottom of the furrow. It also means ploughing at a comparatively slow speed.
“You also need to be aware of what you may be ploughing back up.”