Where pastures are being reseeded in the autumn, weed control should be an integral part of the reseeding programme.
“Reseeding gives a big boost to grass quality and output, however the benefits are seriously eroded if weeds in the new reseed are not controlled early,” said Chris Maughan, techncial manager with Whelehan Crop Protection.
He said chickweed and docks are big problems in new reseeds.
“Seedling docks can be a major problem and if not controlled at the seedling stage, dock roots can grow up to a metre deep and have a devastating effect on grass output.
“Teagasc research has shown that treating docks at the seedling stage with an effective systemic herbicide in a new reseed will result in a dock-free pasture for the following five years.
“Chickweed is another serious problem and can smother the new grass, resulting in a very patchy sward. The biggest risk is from common chickweed but mouse-eared chickweed can also be a problem,” added Chris.
Weed control in autumn-sown reseeds
When it comes to choosing a herbicide for autumn-sown reseeds, Envy is an ideal choice.
Manufactured by Corteva Agriscience and distributed on the Irish market by Whelehan Crop Protection, Envy contains two powerful ingredients: florasulam and fluroxypyr.
It is powerful on seedling docks and common and mouse-eared chickweed and is also highly effective on a range of other weeds including buttercups, dandelions, daisies and plantains.
Envy works well in cooler conditions and has the advantage of being applied up to November 30.
It can be applied from when the third-leaf visibility stage of the grass occurs. The application rate to new reseeds is 1.5L/ha in 200L of water.
Where it is not possible to apply a post-emergent autumn spray of Envy to a new reseed, it is vital that the weeds are controlled early in the spring. In this situation, Pastor Trio, is the herbicide of choice.
It contains three powerful ingredients, florasulam, fluroxypyr and clopyralid. This combination ensures a wide spectrum of control.
In addition to controlling the same range of weeds as Envy, it is also powerful on thistles which can be a serious problem in new reseeds. It is also effective on annual weeds such as redshank, charlock, mayweed and fumitory.
As with Envy, Pastor Trio, should be applied to new reseeds at 1L/ha in 200L of water.
More farmers opt for over-sowing clover
The withdrawal of the active ingredient 2,4-DB has greatly limited the options in clover-safe herbicides.
With clover susceptible to Envy, Pastor Trio and other systemic herbicides that kill broad-leaved weeds, and the availability of clover-safe herbicides severely limited, the need for excluding clover from the original grass mixture has become more important.
The technique of over-sowing clover into the new pasture after weeds are controlled was pioneered by Teagasc at Moorepark and is now being used by a growing number of farmers.
This practice involves sowing ryegrass only, applying a post-emergence herbicide and then over-sowing clover into a clean sward at a later date.
Clover is mixed at 5kg/ha with PK fertiliser and spread at 2.5 bags/ha in two runs at right angles to each other.
The use of a quad bike fitted with a slug pellet applicator can also be an effective method of broadcasting the clover seed.
Around 7,500gal/ha of watery slurry should be applied after broadcasting the clover seed. This will help to wash in the seed and seal the ground in order to reduce moisture loss.
The technique can also be used to introduce clover into established swards. It can be very successful after silage cutting and also works well in grazed swards, however tight grazing before and after over-sowing is vital.
The clover can be over-sown three months after Envy and Pastor Trio are applied. In the case of autumn-sown reseeds, this means over-sowing the clover the following spring/early summer.
Spot-treating weeds
Where weeds such as nettles, thistles, briars and docks are present at fences, ditches and hedges, there is still an opportunity to get rid of them with a spot treatment of Grazon Pro. This contains two powerful root killing ingredients, triclopyr and clopyralid.
As well as nettles, thistles, docks and briars, it is also highly effective on buttercups, gorse, cow parsley and hogweed.
Grazon Pro should be applied at a rate of 60ml in 10L of water using a conventional knapsack sprayer, a quadbike sprayer or a suitable lance on a tractor mounted sprayer.
Still time to kill docks
There is still time to kill docks in grazing pastures and have a clean, productive sward for the remainder of the grazing season and for next year and beyond.
Pastures that were cut for silage or dock-infested grazing pastures that were recently topped should now be at the right stage for effective treatment.
When it comes herbicide choice, there is nothing to beat the specialist product Doxstar Pro. Containing two chemicals, triclopyr and fluroxypyr, it ensures the most effective kill of the dock root system. It is also highly effective on chickweed and dandelions. Unlike dicamba-based products, it does not result in any check to grass growth.
For best long-term control with Doxstar Pro, docks should be actively growing and be 15-25cm high or across.
As with all systemic herbicides, keep animals off pasture for seven days after spraying with Doxstar Pro.
Autumn weed control of thistles
Where thistles were not controlled earlier in the season, there is an opportunity to get rid of them with a late-August/September application of Thistlex, the specialist thistle herbicide.
It contains the active ingredients triclopyr and clopyralid, which are absorbed right down to the roots of the thistles.
Animals leave 30cm ungrazed around each thistle plant. Just fifty thistles per 20m2 – which is very common in thistle-infested swards – can mean a drop of 50% in grass dry matter yield. This highlights the importance of eliminating this pernicious weed.
For best control, thistles should be actively growing, have four to 10 leaves, be 15-25cm high and before a seed head appears.
Thistle-infested swards that were recently cut or topped should now be at the right stage for effective treatment with Thistlex.
For further information on any of the products discussed above and farm weed-control, click here.
