Desiccation post-acid is doable

Earlier drought means destroying maincrop potato haulm before lifting should be easier this season.

But growers should still strive for the most appropriate technique to save money yet protect tuber quality, say specialists.

With retailers urging growers to shun acid desiccation, there are plenty of effective alternatives, including increasingly popular flailing, to do the job more cheaply, says Masstock’s Malcolm Smith.

“With the three desiccants – Reglone, Harvest and Spotlight – and improvements in modern flailing equipment, we now have the tools. It’s just a matter of learning where best to use them.”

Getting rid of haulm in unirrigated or only partially watered crops should be straightforward, as many are already senescing, says Mr Smith.

But choices for well-irrigated crops, on which growers wish to delay desiccation to maximise yields and desired tuber size, must take account of soil moisture and variety, he advises.

Single spray

For determinate varieties – eg Estima, Premier and Wilja – with insignificant haulm a single spray of 3 litres/ha of Harvest once the crop has started to senesce, and if the weather isn’t too wet, should do.

“An alternative for more vigorous canopies, provided a soil moisture SmartTest permits, is Reglone at 1.5-2 litres/ha followed by more Reglone (up to the total desiccation dose of 4 litres) or Spotlight.”

New Syngenta support for 1 litre/ha of Reglone irrespective of soil moisture is particularly welcome, says Mr Smith.

“It’s often enough to open up the canopy for the following treatment and it does increase flailing rates.”

The real challenge is on indeterminate varieties, such as Cara, with bulky canopies.

Three years of Cambridge University Farms work shows that combinations of the three desiccants provide the flexibility to tackle the most severe haulm, vigorous and not senescing, says independent consultant Chris Ursell.

“What’s needed in these situations is a programmed approach.

For example, opening up the canopy with 2 litres/ha of Reglone followed by full-rate Harvest or Spotlight to complete the burn down.

On some soils flailing may replace the initial spray, and a desiccant applied at the time significantly cuts regrowth.

The latest machines follow ridges more closely and avoid masking the stem spray target with cut haulm, says Mr Ursell.

“But they can be slow and are not ideal on heavier-bodied silts because they can cause compaction.”

However, work at Scottish Agronomy shows that spraying Reglone a week before flailing to leave just 15-20cm of stem as a target for following sprays can speed the task, cut the risk of vascular browning and save money.

“There’s no definitive best route to desiccation,” says the firm’s Eric Anderson.

“You have to find the best way for individual crops given the variety and conditions.

“Flailing is not universally helpful.

If the soil is very dry it can actually dislodge soil and cause more green tubers.

And depending on conditions there is a risk that it can spread blight and blackleg.”

The SA trials found that pre-flailing Reglone at 0.5 litres/ha and 1 litre/ha (the newly supported dose) boosted workrates by 31% and 52%, and cut fuel costs by 24% and 34%, respectively.

A two-pass acid programme costs about £90/ha (£36/acre), says Mr Anderson.

By contrast, flailing followed by a spray is about £70/ha (28/acre) with pre-spraying reducing that by about £7/ha (£3/acre).

Dual Reglone treatment, is cheaper still at about £45/ha (£18/acre).

But the CUF work suggests it may not always provide the complete answer.