Pastor Trio – the tailor-made weed killer for reseeded pasture

Weeds, when established, can greatly reduce the performance of a grass sward and research has shown that every 1% infestation of weeds (like docks or chickweed) can result in a 1% reduction in grass yields.

Controlling weeds in newly-sown leys is critical to the establishment and performance of a new sward. However, this can be difficult when weeds like docks and chickweed are present.

Pastor Trio, the new herbicide launched last year by Dow AgroSciences, represents a major advance for weed control in reseeded pasture. Containing the powerful active ingredient florasulam, Pastor Trio is imbued with the most advanced technology in weed control.

It also contains the two tried and tested ingredients – fluroxypyr and clopyralid. The cocktail of these three powerful ingredients – with different modes of action – ensures a very wide spectrum of weed control in reseeded pasture.

PastorTrio is especially powerful on docks and chickweed, two major weed hazards in reseeded pasture. It is equally effective on thistles, dandelions, buttercups, redshank, fat hen, charlock, mayweed and fumitory.

Common chickweed


Many reseeded pastures, in recent weeks, have shown a very high infestation of weeds. Docks appear to be coming through in big numbers.

Pastor Trio provides the perfect opportunity to kill docks at the seedling stage. If uncontrolled, dock roots can grow to a meter deep and can devastate grass yields. Hitting them early is imperative.

Chickweed, if left uncontrolled, can effectively smother the grass. If this is not tackled early on, the reseed – next autumn and beyond – will be very patchy at best. Common chickweed causes the biggest problems, but mouse-eared chickweed can also be a problem.

Thistles, especially the spear thistle, appear to be a much bigger problem in recent years in newly-sown pastures. Dandelions and buttercups, even in fields that were burned off before reseeding, can become a major problem.

These tend to be worse where reseeds are direct drilled or power harrowed instead of using the traditional ploughing method.

Pastor Trio will give great control of all of these. It should be applied at 1L/ha in 200L of water from the third leaf visible stage of the grass. It can be applied up to August 31.


Pastor Trio is also approved as a post-emergent spray in maize. As well as controlling all the weeds listed above, it is also highly effective on black nightshade, field bindweed and black bindweed.

It should be applied at 1L/ha between the three and six leaf stage of the crop and before the maize is over 20cm tall.

Pasture Trio at a glance

  • Contains three powerful ingredients – florasulam, fluroxypyr and clopyralid – ensuring a very wide spectrum of weed control;
  • Weeds controlled include: docks; chickweed; thistles; fat hen; dandelions; buttercups; mayweed; charlock; fumitory; and orache;
  • Tailor-made for reseeded pastures;
  • Apply at 1L in 200L of water per hectare from the third leaf visible stage of the grass in reseeds;
  • Also highly effective in permanent pasture and in silage swards;
  • Apply at 2L in 200-300L of water per hectare in established grassland;
  • Can also be used in maize.

Perfect for silage and pasture

Pastor Trio is also the perfect solution for buttercups, dandelions, docks, thistles and other weeds in silage swards and permanent pasture.

Apply at a rate of 2L/ha in silage swards at least four weeks before silage is cut. This ensures the chemicals are fully translocated to the root system, enabling the most effective weed kill.

In permanent pasture, keep animals off the grass for seven days after application of Pastor Trio.

Add clover after weeds are controlled

As clover is susceptible to Pastor Trio and other herbicides that kill broad-leaved weeds, a growing number of farmers are now excluding clover from the mixture at reseeding, controlling the weeds and then over-sowing, or surface seeding, the clover into a clean sward at a later stage.

The technique of over-sowing clover with phosphorous and potassium fertiliser was developed successfully by James Humphreys of Teagasc Moorepark. He pioneered the system at the Teagasc dairy research farm at Solohead, Co. Tipperary.

In many cases, the effects of heavy infestations of weeds far outweigh the benefits of clover in a reseeded sward. The best decision economically may be to control the weeds and then add the clover.

Key steps:

  • A high seed rate of 2kg/ac of white clover should be used;
  • Use a compound fertiliser such as 0:7:30. The fertiliser should not contain nitrogen;
  • 2kg of clover is mixed by hand in the fertiliser spreader with each bag of 0:7:30. Mixing is best done in the field to avoid the clover separating out;
  • The fertiliser should be spread at one bag/ac in two runs at right angles to each other;
  • After spreading, around 3,000 gallons per acre of fairly watery slurry should be applied to wash in the seed and seal the ground in order to lower moisture losses.

Silage swards

The technique is also very effective after first-cut silage and in permanent pasture, but it is important to have it tightly grazed. It works best where moisture levels are good.

When weeds account for 20% or more of the field, it will pay to kill the weeds and re-introduce the clover later. The over-sowing can be done 30 days after Pastor Trio is applied. Click here for more information on Pasture Trio