Dealing with black-grass in stubbles is the first step in a successful weed control programme for the year ahead, Bayer CropScience is reminding growers.
People have several options at this stage of the season, but the biggest factors are crop choice and soil moisture.
“It obviously depends on what crop is following what,” says Ben Giles of Bayer, “oilseed rape after wheat is usually pretty tight, whereas if you’re late drilling winter cereals then you might have eight weeks or more to tackle weed problems.”
The main tactic is to promote a flush of weeds – black-grass and anything else that’s lurking in the soil – and kill them off. For this, soil moisture is key but it can be in short supply in August so it’s a case of waiting for moister conditions for weeds to start growing.
“If you are trying to encourage black-grass, do everything you can to create seedbed conditions which will retain moisture and promote germination. Remember some brome species are different and need to be left alone and not moved if these are a problem.
“After harvest, many people like to cultivate the soil with discs but this can just end up drying out any moisture left in the ground and so some form of consolidation is important to create the false seedbed and encourage a flush.”
“I know of some people who run the drill through this false seedbed to replicate exactly what happens when a crop goes in.
“Overall, there are whole range of tricks and methods which are geared to particular soil and conditions – it’s all about learning from what has or hasn’t worked in the past.”
One additional thing to consider is the new stewardship guidelines for glyphosate usage which recommend only two applications per crop. Ben Giles believes that the new guidelines shouldn’t have a big effect on control programmes: “It means you can get rid of two flushes of black-grass, the first will be whenever the stubble starts to green up after harvest – the second just before drilling.
“You have to remember that the potential size of the black-grass seedbank can be enormous so you can’t expect to eliminate every seed.
“What you are trying to do is create the best conditions for pre-emergence products by killing as many as possible and getting plant numbers low enough for pre-ems to clean up the field.”