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Weed Control in Productive Grassland

Weed Control in Productive Grassland

Weed control is a key element of productive grassland and should involve the adoption of an integrated pest management plan approach where cultural control methods are considered before the use of pesticides. Eamonn Dempsey, Teagasc Advisor, Tralee has advice on how best to approach weed control

Know your soil fertility status

It is important to study a recent soil sample analysis to know if there is a need for lime and if phosphorus and potassium are at an optimum level to grow more grass and as a result limit space for weeds. Established grassland is defined as a field in pasture for over a year and will be competition against common weeds such as docks, thistles, nettles, chickweed, buttercup and ragwort.

When to apply herbicides

Once you have identified a weed problem and the weeds to be treated, herbicides should then be selected and applied at the correct stage of growth. Generally herbicides should be applied when weeds are healthy and actively growing from seedling stage to just before flowering.

Docks, probably the most challenging weed to control,  should be sprayed when actively growing in the summer months with a product that will be fully translocated down to kill the root. Teagasc trials have shown that longer term control of docks can be achieved by applying a suitable herbicide onto small docks shortly after reseeding. The following year docks will fail to establish due to competition from the sward. There are some clover safe products on the market for dock control e.g. legumex DB type products, however for the treatment of chickweed, nettles, thistles, dandelion there are limited options if clover is present in the sward. If clover is present or you intend to oversow clover you must select a clover safe product. Forefront T contains two chemicals aminopyralid and triclopyr which makes it the product of choice for docks, nettles, thistles, buttercup, chickweed, dandelion and ragwort, but it is not clover safe. If the stem and seeds are present in weeds, top the weeds and spray the regrowth a few weeks later.

Remember land parcels selected for Glas action Low Input Permanent Pasture cannot be topped between 15th March and the 1st July annually and pesticides are not permitted except for spot treatment of noxious and invasive weeds.

Normally animals do not eat weeds in pastures unless grazing is extremely restricted, however it is important to keep animals off pastures or avoid cutting silage for 7 days after spraying. In the case of ragwort do not allow animals back into treated fields until ragwort has completely rotted down and become unpalatable.

Follow recommendations

Controlling broadleaved weeds in grassland will maximise grass yield, improve silage quality, increase pasture utilisation and will eliminate health risks to livestock. Apply approved products for the target weeds at the correct rate, stage of growth, don’t spray if there is a risk of drift or heavy rain and adhere to buffer margins. Follow the recommendations of Integrated Pest Management and under the Sustainable Use of Pesticides Directive (SUD) the person applying the pesticide must be registered as a Professional Pesticide User.

For more on weed control check out this Environment Edge podcast episode below with Kieran Kenny, Teagasc ASAAP Advisor 

Kieran discusses the importance of good practice when using pesticides and alternative methods for weed control. For more episodes and information from the Environment Edge, visit the show page at: www.teagasc.ie/environmentedge/

You might also like to read Best Practice use of pesticides

Teagasc Advisors are regular contrbutors of articles on topics of interest to farmers here on Teagasc Daily Contact your local Teagasc advisor for more advice.