Docks are the key weed that infect nutrient rich grassland in Britain and Ireland, with research from Ireland undertaken by Teagasc showing that for every 1% of dock ground cover, there is a 1% loss of grass dry matter yield.

With the digestibility of docks up to 35% less than grass, and docks generally avoided in a grazing situation by cattle, controlling this weed is an important part of grassland management.

Speaking at a product launch of two new grassland sprays last week, Andy Bailey from Dow AgroSciences recommended treating the problem when docks cover more than 5% of a field. As a rule of thumb, if an area of 5m x 7m has more than five docks present, then it should be sprayed. Below that level, individual plants can be controlled with a knapsack sprayer.

“The dock is quite an incredible plant. One mature dock can produce more than 60,000 seeds, and these seeds can survive for 50 to 80 years in soil,” said Bailey. Quite often in a new reseed, a flush of docks will come in the first year as a result of new plants forming from this dormant seed.

A mature plant has an enormous tap root, which can be up to 1m deep. The challenge therefore is to get enough herbicide absorbed through the leaves and into the root system to kill the entire plant. As a result, spray should only be applied when plants are young and actively growing.

The same is true of thistles. There are two common perennial types – creeping thistle which tends to grow in patches or clumps, with each patch usually a single colony linked by a massive root structure underground; and the spear thistle, which grows as a single plant with a large single taproot.

Spray

With tighter controls on who can apply spray, more farmers are now using contractors to control weeds. That has led Dow to look at whether new spray technology (air inclusion nozzles on sprayers rather than flat fan nozzles) will allow their main products to be applied using lower volumes of water (200 litres/ha versus 300 litres/ha). The potential benefit for the contractor is higher efficiency, with more hectares covered in less time.

The trial work showed that where air inclusion nozzles are used there is no negative effect from reducing water volumes down to 200 litres/ha.

However, where sprayers are fitted with conventional flat fan nozzles, the historic recommendation of 300 litres/ha still remains.

Two new weed control products have been brought to market by Dow AgroSciences.

The first product, Envy, will be the cheapest herbicide available within the Dow range, and is targeted at low input grassland, offering control of weeds such as daisies, buttercup, dandelions, chickweed and docks. Used on established grassland at a rate of two litres/ha, or 1.5 litres/ha on new sown leys, it can be applied any time between 1 February and 30 November (weeds should be actively growing).

The second product is Leystar. It is being marketed by Dow as a new way of controlling weeds in new sown leys, offering good control of chickweed, buttercups, seedling docks and thistles. It can be applied to new sown leys (once the grass plant has three true leaves) at a rate of one litre/ha. It has a label recommendation limiting use between 1 February and 31 August, so it is probably restricted to a spring or summer reseed. Leystar also has approval for post emergent weed control in maize (up to the three- to six-leaf stage).

Both Envy and Leystar contain Florasulam, the first new active ingredient approved for use in grassland for 12 years.

Other Dow grassland chemicals include Forefront, Doxstar Pro, Grazon Pro (knap sack sprayer application) and Thistlex. With Forefront and Doxstar Pro not recommended for use in new sown leys, the addition of Envy and Leystar is important in the Dow product portfolio.

Clover

Neither product is clover-safe, so farmers who want to introduce clover in a new sward, but also want to control weeds, will have to look at other alternatives on the market. Farmers report varying levels of success with clover-safe products, but generally they work best when weeds are at a seedling stage (not growing from established roots). The other option is to control weeds now, and introduce clover at a later date.