Desiccation post diquat…planning starts pre-season

February 4 last saw the last date of use pass for diquat. It had been used as an extremely efficient desiccant and herbicide for many years.

Shay Phelan – Teagasc Crops Specialist – outlined some of the options available to farmers now that the product is off the shelves.

While chemical options are still available they take more time to work. Both cultural and chemical methods can be aided by some decisions that farmers make ahead of and during the season.

For example, choosing varieties with different levels of haulm longevity may be an option.

However, 60% of the potatoes grown in Ireland are Roosters – as the market demands – and this variety is rated at 3 (long longevity) on a scale of 1-4 for haulm longevity.

Kerr’s Pink potatoes have very long longevity with a rating of 4 and Home Guards and Premiers – not commonly grown in Ireland – have short haulm longevity at a rating of 1.

Reducing nitrogen (N) rate may also help to speed up desiccation if it is a possibility. Where a large amount of N is applied, crops will most likely stay greener for longer, so farmers may decide to reduce N rates in order to make it easier to desiccate crops.

Chemical options for desiccation

In reality, chemical options currently available take more time to work than diquat did.

There are chemical options still available for desiccation. However, these products need a desiccation time of four weeks minimum, meaning the last date for application will be the end of August for a harvest date of October 1.

This means the first of two applications should be applied by August 20.

Haulm topping

Haulm topping involves topping stalks to 8in to leave enough leaves to take up fungicide and desiccants.

Crops need to be cut evenly and where stalks are very low to the ground they need to be lifted.

It is important to remember that when stalks and leaves are chopped there is a risk of disease and infection. This means that a fungicide needs to be applied as well as a desiccant. This should be done within 48 hours of topping.

Some more options are listed below including electrocution. The image at the top of the article shows Case IH’s AGXTED XPower which can be used to control weeds, burn off grassland and has potential to be used in potato desiccation.

Other potential options include:
  • Haulm pullers;
  • Salts;
  • Electrocution;
  • Nutrient toxicity;
  • Natural death.

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