Cereal growers with black-grass that hasescaped autumn control strategies need to seriously consider re-drilling badlyaffected areas rather than placing undue pressure on herbicides next spring,warns leading agronomy firm Hutchinsons.
Seedbed conditions this year generallysuited residual herbicide chemistry and stale seedbeds, so growers who stilldid not achieve adequate black-grass control need to decide sooner rather thanlater what to do with the worst areas, says the firms technical manager DickNeale.
Every year there are more cases in badblack-grass areas, where pre- or post-emergence control hasnt worked properly,where the most appropriate route forward is to spray-off cropped areas withglyphosate and start again in the spring.
Its a big decision to make, but one thatis increasingly being faced up to, especially among early drillers.
If youre heading into spring with a largeblack-grass population, then its no use relying on Atlantis (mesosulfuron +iodosulfuron) to solve the problem. Atlantis can still control black-grass, butits got to be used in the autumn when black-grass is actively growing at theone to two-leaf stage.
Time is of the essence
The sooner any re-drilling decision is madethe more time growers have to plan what to do with land in the spring to getthe best crop possible and maximise black-grass control, Mr Neale says.
He acknowledges there is no clearthreshold black-grass population that dictates when the decision to re-drillshould be made, as much depends on the yield potential of the crop and whatlevel of competition it can sustain.
If its down to pure numbers then zerotolerance on black-grass is the best solution in an ideal world, as relativelylow levels of black-grass have a high impact on yield.
For example, just 12 black-grass heads persquare metre at harvest can result in a 5% yield loss in wheat. Depending onwhen that black-grass establishes that equates to a maximum of around fiveblack-grass plants per square metre, he explains.
A lot of earlier drilled crops this seasonhave good yield potential so may be able to sustain higher black-grasspopulations, he says. A 1015% yield loss on a 12t/ha crop still gives a goodyield at the end of the day.
But growers also need to consider totalherbicide expenditure and the longer-term accumulation of weed seeds in thesoil profile.
Dont rely on herbicides alone
Mr Neale says there is little doubt thatexisting chemistry is failing with the increased incidence of herbicideresistance, but the main actives can still deliver good efficacy if givenfavourable conditions to work.
A key part of that requires getting black-grasspopulations down to a level that gives autumn residual chemistry a decentchance. In most cases thats less than 100 plants per square metre, but werestill seeing people trying to control populations of 400600 plants/m2, whichisnt sustainable.
If the decision is taken to spray-off acropped area because of black-grass, he says it is vital to make sure thereplacement crop helps weed control as much as possible. He believes springbarley, or spring oats offer the most effective answer due to their competitivenature. Spring barley also has a widerange of suitable effective herbicides approved for use on the crop, but forspring oats this is restricted to DFF.
Dont just pick a spring crop thats cheapto establish and offers a high price or big gross margin. Consider it as partof your longer-term black-grass control strategy as well. It would be a goodtactic to spend some of the intended in-cereal black grass herbicide budget onhigher seed rates in spring peas or beans to provide a more competitive plantstand.
Lincolnshire-based Hutchinsons agronomist PhilVickers works across some of the countrys worst black-grass land and alsobelieves re-drilling can be an answer to getting on top of the problem in thelonger-term. Its certainly not an ideal solution, but bigger stacks ofchemistry simply wont work and if we dont do something, the problem is onlygoing to get worse.
For him, delayed drilling and getting in asmany stale seedbeds as possible is the key to effective black-grass control.
A lot of farms have managed three kills ofblack-grass before drilling this autumn, which has probably taken out 2,0003,000black-grass plants per square metre. But youve got to have the nerve to holdoff drilling until at least mid-October or early to mid-November on the moreproblematic land.
Basedecision on whether to re-drill black-grass-affected crops on the potentialyield loss and impact on weed seed bank if crop is taken to harvest
Replacementcrop must offer a good black-grass control opportunity spring barley or oatsbest
Tryto encourage a flush of spring-germinating black-grass before spraying the cropoff e.g. quick pass with rake, but
Waitfor the soil temperature to reach above 8 degrees Celsius black-grass willnot germinate below this
Sprayoff with glyphosate ahead of drilling