Farm Ireland

Saturday 18 November 2017

Harvest desiccated crops very soon

Dr Richard Hackett

While harvesting has begun in the south, combines across the country have been on a rain check for the past 10 days. Harvest reports to-date have been mixed, with good-quality grain but with no record-breaking yields.

There are also variable reports about other aspects important in the success of the winter barley crop, such as low moisture grain and high straw yields. Many winter barley crops have been desiccated, and it is important to harvest these crops as soon as possible.

After harvest, however, the desiccated straw will be in a much better position to be baled behind the combine than naturally senesced crops.

Pre-harvest glyphosate

Cereal crops are heading for the stage where pre-harvest glyphosate can be considered. The main reason for the use of pre-harvest glyphosate is to control perennial weeds, particularly scutch, but other weeds are also usefully controlled at a pre-harvest stage.

Pre-harvest application has many advantages over post- harvest applications. The main benefits are more green leaf on the weeds, and higher temperatures and growth rates at that time of year to increase uptake and efficacy of the product.

But there are also disadvantages, such as tramping of crop at headlands, which reduces yield, and the strict time constraints for subsequent crop establishment to remain compliant with the Nitrates Directive.

Where applications of an autumn desiccant have been applied, the subsequent crop must be sown to emerge within six weeks of application. For example, desiccating a crop this week, the subsequent crop must be sown to provide for its emergence by September 1, or else shallow cultivation must be practised on this land in the interim.

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Where pre-harvest glyphosate is applied on land destined for spring cropping, shallow cultivation must be carried out post-harvest to stimulate natural regeneration.

Rotational application of glyphosate on a three-year basis is necessary to control perennial weeds, such as scutch grass, and pre-harvest application is an efficient, effective way of carrying out this function.

But in the absence of perennial weed control or elimination of green material in a crop, there is no advantage to pre-harvest glyphosate application and it imposes a net cost on production, and perhaps even a cross-compliance sanction if not managed correctly.

Oilseed rape

Many crops are ready for desiccation with a diquat or glyphosate-based desiccant. The correct stage to desiccate is when the majority of seeds in the middle pods of the main stem are brown/black in colour.

It's moving past optimal timing for glyphosate, as crops naturally senescing will not take up glyphosate as successfully as greener crops. However, use glyphosate where perennial weed control is an objective.

The use of a pod sealant can provide some insurance if harvest is delayed or if weather is windy post-desiccation. Pod sealant is expensive and is not necessary under normal circumstances, but can reduce pod shatter significantly.


With the recent weather, pay attention to fungicide spray intervals, and if showery weather is dominating, use Revus, as it has the quickest drying time of all the strong fungicides.

If the weather remains dry for one to two hours post-application, products like Infinito, Ranman, Consento, Valbon or Acrobat will perform as well.

Include a Cymoxanil-based product to provide a 'kick back' to the fungicide mix if the spray interval is delayed. And apply the first Methiocarb- or Metaldehyde-based pellet to control slugs in susceptible varieties before the canopy closes.

Irish Independent