Fine-tuning rates keeps emerging weeds pegged
Fine-tuning rates keeps emerging weeds pegged
RATES and timings of autumn cereal herbicide partners isoproturon and diflufenican may need to be adjusted to maintain maximum control of fast-emerging blackgrass and broad-leaved weeds, according to herbicide specialists.
Where blackgrass emerges very early in dry soils, limited commercial experience shows that applying 1 litre/ha of ipu when blackgrass is spearing will control that first flush.
The spray should be applied when leaves are wet, either in fog or in the early morning or late evening, says ADASs Jim Orson. "The remaining dose, together with a low dose of another herbicide to boost activity, can then be applied when conditions are more favourable later in the autumn." That approach will also avoid luxury uptake of ipu by fast-growing plants, which can scorch crops.
If the Indian summer continues, conventionally-timed applications may still run into trouble, he adds. "In a warm autumn up to 30% of ipu can be broken down within a month. That may not matter for blackgrass control, but it can reduce control of spring-germinating weeds like poppy and volunteer oilseed rape."
Levels of those weeds shocked some growers last year, he adds. But increasing the rate of partner product diflufenican (DFF) above the usual half rate of 50g/ha will maintain control. Exact rates depend on the date of application.
Most other broad-leaved weeds will be controlled by a half-rate application with IPU, leaving growers free to concentrate on cleaver control in the spring. "Cleavers will be left weak and more susceptible to spring follow-up treatments like Starane or Eagle. That gives more flexibility as far as timing is concerned and may allow rates to be reduced."
However, maker Rhône-Poulenc reckons some growers could benefit from boosting diflufenican rates to control that weed. "It is useful to use a full rate of 100g to get on top of a difficult situation," says the companys Gordon Anderson-Taylor.
"That extends the period of activity well through the winter, and may allow growers to control remaining cleavers with a cheaper product in the spring. That could reduce the overall cost of the weed control programme."
Higher rates also give better control of larger weeds prevalent in early-drilled crops, and may avoid a costly sequence of products, he maintains.
Alan Bide of Hampshire Arable Systems would consider raising rates to control large numbers of cleavers or poppies. "But it may be more cost-effective to stay at 50g/ha and top up with higher rates of Starane and HBN in early spring."
Such an approach means the savings made by reducing the DFF rate can pay for the spring chemistry, says Gerald Collini of 3-Shires Services, Northants.
A half rate also cuts the cost of establishing a following crop which is sensitive to the herbicide, like oilseed rape, since residue levels are often low enough to allow direct drilling, says Mr Collini.n
Adjust cereal herbicide rates and timings to reflect weed development and spraying conditions for best results this autumn, urge specialists.
AUTUMN HERBICIDES
• Consider split ipu application for early blackgrass control.
• Warm soils can cause rapid ipu degradation – increase DFF to boost broad-leaved weed control.
• Boosting DFF rates can lower overall weed control costs.
• Watch following cultivations.