Silage Advisory Centre

It has been a challenging season for grassland farmers with the cold, late start followed by prolonged dry spells, which knocked grass growth significantly in many areas.

Weeds, such as docks and thistles, whose roots penetrate much deeper than grass, have not suffered as much - able to reach water in the lower soil horizons. Indeed infestations have been really noticeable this year, as the weeds have towered above the struggling grass.

Where weeds grow grass does not. At any level of infestation, they pose a threat to productivity as they compete directly for light, water, nutrients and space. SAC trials showed that a 10% infestation of docks causes a 10% loss in yield, or one trailer load of silage in ten.

Having weedy fields also upsets many farmers – causing ‘emotional’ aggravation, especially in highly visible areas next to roads and driveways. 

Autumn applications

 Controlling pernicious weeds is not just a job for the spring. High levels of lasting weed control can be achieved from applications of translocated herbicides such as Doxstar and Pastor in the autumn, although the same application rules apply.

Weeds should be at the optimum growth stage, actively growing and healthy, not stressed by drought, disease or pest attack. Ideally docks should be at the rosette stage up to 250mm high or across; thistles also at the rosette stage up to 200mm high or across. If the weeds are flowering or setting seed it is too late.

“The unusual season actually presents a good opportunity for weed control in grassland,” says Dow AgroSciences technical specialist David Roberts. “Weeds have been more visible this summer, so farmers have seen exactly what the main problems are, and which areas are worst affected.

“If weeds are at differing stages across a field, topping will bring them down to one level and encourage an even re-growth. The weeds should be perfect for spraying two to three weeks later.

“Doxstar and Pastor do not adversely affect grass growth as products based on older hormone chemistry can, so farmers looking to capitalise on an autumn flush of grass growth - by taking a third cut of silage or extending grazing- need not worry.

“They also have long lasting effects – applications made this autumn will still be giving good levels of control in a year’s time. However, if farmers applied a half dose in the spring, they should top up with the second half now, to maximise the effects.”

Tidy-up after last cut

Where a wide range of difficult-to-control weeds such as broadleaved and curled docks,  creeping and spear thistles, nettles, dandelion and buttercup, are present in silage leys, an autumn treatment with a broad spectrum herbicide such as Forefront or Pharaoh, can clear the way for better quality silage next year.

Sales of these two products were suspended in 2008 afterincidents involving alleged damage to some sensitive crops were reported in the UK. This was possibly due to manure that had come from farm animals or horses fed pasture or conserved forage from grassland previously treated with herbicides containing the active ingredient aminopyralid found in Forefront and Pharaoh. 

These products were re-introduced this year in Scotland, Northern Ireland and south west England, but with tight controls to prevent problems with manure management - including restrictions on usage, and a stewardship scheme which makes sure farmers are aware of the implications for subsequent manure management.

“This year Forefront and Pharaoh could not be used on grassland destined for hay and silage or on grassland grazed by horses,” says Dow AgroSciences principal biologist Andy Bailey. “However, it can be applied to established grassland after the final cut has been taken, provided it is then grazed by cattle or sheep.

“But bear in mind that where silage, hay or haylage is produced from this area next year, it must stay on the farm. And any manure subsequently produced from animals fed on this forage, must also stay on the farm and only be spread on agricultural grassland.”