Advice from Teagasc: Glyphosate still available for pre-harvest use

Losing glyphosate would make tillage farming very difficult.

As re-registration of glyphosate rumbles on in the corridors of the EU, we await the outcome with bated breath.


Applying pre-harvest glyphosate to a crop will give effective long-term control of scutch, thistles, perennial sow thistle, etc.

The best results are achieved when the weeds are actively growing in moist soils.

Leaving glyphosate application until after the harvest is not as effective on these perennial weeds.

A sizeable proportion of growers also use pre-harvest glyphosate as a harvest aid.

The benefit of applying pre-harvest glyphosate to uniform, weed-free, standing wheat crops is marginal, but it is of benefit in barley.

Applying pre-harvest glyphosate also has implications as regards cross compliance, as these fields should have a green cover (sown crop or natural regeneration) established within six weeks of application.

Crops intended for seed should not be treated.

Is my crop ready for glyphosate?

From 14 days before the normal harvest date, collect 20 grains from the centre of several ears.

Press your thumbnail firmly into the grain, and if the indentation holds on all the grains, the crop is ready for spraying (at or below 30% moisture content, to avoid a yield penalty).

Target weeds must be green, actively growing and accessible to the spray.

A minimum of five to six hours drying after application is essential for satisfactory results with all glyphosate products containing tallow amine surfactant formulation.

Oilseed rape

Glyphosate should be applied when at least two-thirds of the seeds are turning from green to brown in the middle of the main stem.

Harvesting takes place two to three weeks later.

It is advisable to generally use a high rate of glyphosate when burning off the crop (e.g., Roundup Biactive 4.0L/ha) and especially when targeting perennial weeds.

Use 200-250 litres/ha of water to get good coverage of the crop.


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