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Why an old reliable is still the best treatment option when reseeding

It's been the subject of a lot of controversy in recent years, but Teagasc advise that glyphosate (Roundup) remains the most effective option for farmers when reseeding, writes Michael Keaveny


Teagasc advise that Glyphosate (Roundup) remains the most effective option for pre and post-emergence spraying

Teagasc advise that Glyphosate (Roundup) remains the most effective option for pre and post-emergence spraying

Teagasc advise that Glyphosate (Roundup) remains the most effective option for pre and post-emergence spraying

While reseeding is an expensive process and can result in an outlay of up to €300 per acre, its costs are more than balanced by a return on investment which can be recouped within the second year of sowing the new sward.

However, if the reseeding process is not done correctly it can greatly reduce the new sward's benefits. As well as investing time in addressing fertility levels, one of the best ways a farmer can ensure the success of a reseed is through the use of pre- and post-emergence sprays to kill weeds which could otherwise destroy the emerging sward.

There are different methods of seedbed preparation, with the most common being ploughing. However, on many farms this is not possible because the ground is too stony, the soil too shallow, the topography too steep or there is no tradition of ploughing.

Minimal cultivation techniques enable successful reseeding to be carried out without ploughing.

However, regardless of the reseeding method, the old sward should be burned off using glyphosate. Despite receiving a lot of unwanted attention in recent times, this is still the most effective spray to use when reseeding, says Teagasc tillage expert Shay Phelan.

"It's a total weed killer, it's relatively cheap, it's safe according to manufacturers, it's also cost-effective and quick," he says.

"If a farmer tried to spray without glyphosate, they would have to use multiple different sprays and it would even double the cost of herbicide use.

"Spraying should be done 10-14 days before cultivation to allow enough time for the active ingredient of the spray to be carried throughout the plant to ensure an adequate kill, but it is important to check the product recommendations.

"It is important to allow sufficient time between herbicide application and sowing the seed. Contact between the seed and chemical may negatively affect germination rates."

Post-emergence spray is also a key weapon in a farmer's arsenal when it comes to ensuring that a new reseed is not overrun by weeds.

"The best time to control weeds is after reseeding," says Phelan. "By using a post-emergence spray, seedling weeds can be destroyed before they develop and establish rootstocks. Established weeds can seriously reduce the yield potential and economic lifetime of the reseeded sward."

One of the main advantages of reseeding in springtime is that it allows for a bigger window of time for post-emergence sprays, as the later that reseeding takes place, the opportunity to apply a post-emergence spray is reduced as ground conditions are often unsuitable for machinery to travel on.

Docks control

Teagasc trials have shown that longer-term (up to five years) control of docks can be achieved by applying a suitable herbicide onto small docks shortly after re-seeding.

Applying the herbicide at this stage of the docks' development results in an almost complete elimination.

The trials have also shown that docks that emerge in the following years rarely establish due to competition from the grass, as the dock seed does not get the correct light signal to germinate. The post-emergence spray should be applied approximately six weeks after establishment, just before the first grazing takes place

"There are several different types of sprays that can be used, with different ones for different types of weeds," says Phelan.

Farmers should look at what they want to control, and make a decision based on what is available to them. Different sprays are available depending on if you want to protect the clover or not.

Different products also have restrictions on how they can be used.

For example, Forefront is a good product but is only recommended for use on grassland that is going to be used for grazing.

It is not to be used on silage or hay ground because there is an ingredient called Aminopyralid that sticks to the lignin in the grass and is deposited in the slurry, which when it is spread can harm the silage the following year.

"Not using a post-emergence spray can harm a new reseed's long-term health," stresses Phelan.

"If you don't get control of weeds early, a sward won't last as long, so there will be a need to reseed on a more regular basis, and you may even have to over-seed in patches where the weeds have out-competed the grass.

"Getting weeds under control as soon as possible after reseeding is vital to the long-term health of the sward."

Indo Farming