Aminopyralid Update - What you need to know before spreading muck and controlling weeds in grassland this spring

UK - February 11, 2009

For the past three years, many contractors have used Forefront, and more recently Pharaoh - herbicides developed by Dow AgroSciences specifically to tackle the major grassland weeds found on their customers' farms.

Based on an active ingredient called aminopyralid, Forefront and Pharaoh have proved extremely effective, and the significant uptake by contractors and farmers reflects how well the product works. 

However, some problems have occurred where manure produced from animals that ate silage, hay or haylage made from grass treated with Forefront or Pharaoh, was dug into soil in gardens and allotments subsequently planted with vegetable crops, which then failed to grow.

Aminopyralid poses no health risk to any animal that eats treated grass, but there is enough active ingredient found in the manure to cause a problem for plants that are sensitive to it. It is therefore very important that any manure generated from Forefront/Pharaoh-treated pastures should stay on the farm of origin.

All aminopyralid-containing products do carry label warnings advising on the appropriate use of any resulting manure and slurry.

"Our current advice on using muck and slurry from treated grass is to spread it only onto pasture or land intended for growing cereals or maize," advises Dow AgroSciences product manager for grassland products Robin Bentley.

"Contractors who are spreading manure on land intended for potatoes, peas or beans should first establish that it has not come from cattle fed on silage, hay or haylage grown from pastures treated with either Forefront or Pharaoh."

Last autumn, Dow AgroSciences sought a voluntary suspension of approval for the sale and use of aminopyralid-containing products, while it strives to minimise the risks of problems re-occurring. Unfortunately, they will not be available for use by contractors this spring. 

Where contractors are looking for weed control options this spring, Doxstar, Pastor and Thistlex are tried and tested alternatives. When applied at their full application rates, these products give the highest level of control of the available products on the market.

For example, treating silage leys four weeks before cutting with Doxstar will significantly increase the amount of grass that ends up in the clamp, and improve silage quality.
 
Applications of 1.5 l/ha will give good seasonal control. To achieve longer lasting results, a full 3l/ha rate of Doxstar can be used. As with all grassland weedkillers, for the best results weeds should be young and actively growing when sprayed.

"Do not let the lack of aminopyralid put customers off controlling broad-leaved weeds in their grass this spring," says Mr Bentley. "This will undo all the good work that has been done in previous years."

"Older products, such as CMPP, (which has had its registration for use on grass revoked), and MCPA do not have the performance needed to deliver a more lasting effect. So, in the absence of Forefront, Doxstar, Pastor and Thistlex are good alternatives, and will do a very good job."

Contractor Comment
North Yorkshire contractor Peter King runs a contracting business in Skipton, and carries out weed control for farmers across North Yorkshire. 

"The golden rule when tackling weeds like docks and thistles in grassland is to 'treat them early', before they have built up an extensive root system, and when they are in perfect condition - so not when the leaves are covered in slurry, or damaged by chain harrowing, or riddled with disease - as this will prevent the necessary amount of active ingredient from getting into the plant.

"Treat docks when they are actively growing with four or five healthy leaves.   Thistles should be at the rosette stage with four to ten leaves and very little stem - long before the flower head goes up, for best effect.

"Weeds are more than an unsightly nuisance - they cost farmers money in lost  production, and reduce the quality of any conserved forage made from the grass.

"Not treating is not an option, as this will compound the problem. As will topping or spraying with products like MCPA, which really just remove the above ground tissue, making it harder to deal with the following year when the root systems have extended further and deeper. 

"And with the high price of fertiliser, it just doesn't make sense to waste any of it by 'feeding' the docks. They will be more than happy to use it to increase their biomass above and below ground, making the situation even worse."