Black-grass seedbank requires brutal focus

Richard Peake of Harlow Agricultural Merchants suggests that 80% of the poor levels of black-grass control last autumn is down to farmers not being able to use pre-drilling glyphosate. He suggests that the combination of complacency following high levels of weed control in autumn 2010 coupled with the inability to use stale seedbeds in autumn 2011 has come back to bite many growers with ferocity.

"The major priority pre-drilling needs to be brutal in order to get black-grass plant numbers down; otherwise it is going to be very difficult to get anywhere near acceptable levels of control from herbicide programmes, particularly with Atlantis failing and fading fast," he warned.

He said that “ploughing is also going to have to be part of the solution on many farms, which may not be a palatable thought, but it could make all the difference as it will bury more seeds than it brings up. Going forward for some farms, the black-grass may become so bad that alternative rotations or even three to four years without winter cropping could be necessary to get back into control.”

In trials carried out by Richard Peake where he took plant counts using fixed half metre square quadrats, he has found that core to a successful herbicide programme should be pendimethalin + flufenacet (Crystal) + diflufenican (DFF).

"In the two years of trials, we have counted emerging black-grass plants that have come through the various treatments on a monthly basis from October through to March. We found that on average 75% of those that made it through a Crystal + DFF treatment will die by March, but importantly they do not start to die until after Christmas.”

He believes that is due in part to the longevity of pendimethalin slowly killing the plants which he decribes as ‘death by a thousand cuts’. “Similar treatments without pendimethalin show only a 50% plant loss. So look at the emerging black-grass and see if the 25% that will remain, are they likely to be a problem? If so another spray needs to be made.”

"Our trials have also shown that this Crystal + DFF black-grass programme should be the bare minimum in programme options and that by adding the adjuvant Backrow/Grounded, growers can expect an improvement in control of between 5-10%. At an increased cost of £1.20/acre this is a no brainer. Backrow/Grounded also reduces spray drift because it is oil based and helps prevent herbicide leaching down into the soil profile where it can affect shallow drilled wheat seed as well as keeping it up in the black-grass germinating zone."

He noted that the trials also show that timing is crucial; "results can be very satisfactory from early post-em provided the residual is applied before the black-grass reaches one leaf; but if you leave applications by a mere one week, the reduction in control levels can be fatal. The trials also indicated that the more robust programme option of Crystal + DFF + chlorotoluron (CTU) is the next best performer - but that with 40% of last year's wheat acreage in Essex being CTU susceptible, only some growers can use it.”

"By far the best performing programme was Avadex granules, followed by Crystal + DFF; it was head and shoulders above the other stacks of actives. This combination also gives a very wide range of weed control including wild-oats and rye-grass."

He suggested that wild-oats are going to become a renewed headache for growers as the usage of Atlantis declines. "Atlantis has been very good at checking wild-oats, but they have been a real issue in 2011/12 and look likely to become increasingly problematic once again over coming seasons."

However the bigger headache is the increased spend that has now become a pre-requisite to growing wheat where black-grass is prevalent. "I would say that for a programme to be effective costs a grower three times more than it did four to five years ago," but he added that not spending is not an option as the weed pressure continues to rise and the number of chemical options declines.