Potato desiccation after diquat

Potato farmers here in Ireland are now in their first season without diquat after it was banned and was to be used up by February of this year.

Diquat was used as a desiccant in potato crops and alternative products on the market do not work as quickly.

It should be noted that 10 European countries have received a derogation from this ban for 2020 – including Austria and Denmark.

Many potato crops are now at or coming near the senescence stage and require decisions about desiccation.

Farmers should first make sure that dry matter contents are correct. Dry matter will decrease by approximately 1% between desiccation and harvest and this needs to be considered.

Tuber size and disease should also be taken into account as the slower desiccation makes things more complicated.

On the latest Tillage Edge Podcast, Teagasc tillage specialist Shay Phelan described the two main methods of haulm destruction now that diquat has been banned here in Ireland.

Main methods of haulm destruction

The first method is going into the crop with a flail and cutting off the stems. This method takes away the majority of the crop’s canopy, but Shay described how a desiccant and blight spray still need to be used as the stems can become infected once cut.

This method is not suitable in wet conditions and so isn’t very practical at present.

The second option is chemical destruction. Spotlight Plus and Gozai are the two main options.

“Chemical destruction is going to be the way to do it but, it is going to take time. Both Gozai and Spotlight take three to four weeks for full desiccation,” Shay explained.

“They’re stem desiccants primarily. They’re not leaf desiccants so we’re just going to have to take our time with those and adjust our harvest dates accordingly.”

Shay continued on to describe how the products currently available can let diseases like black leg spread and stated that more than one application may be needed.

When do these products work best?

The tillage specialist described how these products work best when the crop is at the start of the senescence stage. Applying in the middle of the day in bright and sunny conditions can help to get the maximum effect from these desiccants.

He also noted that water volumes need to be high – up to 400L/ha – to ensure that coverage is achieved down to the base of the canopies.

Disease needs to be controlled, even after the desiccant is applied. Shay stated that this is particularly important where crops are going into long-term storage.

However, he cautioned that while a robust blight strategy is needed in the coming weeks, farmers need to be careful not to exceed the maximum number of applications on a crop.