DESICCANTS CAN burn down potato crops just as effectively as acid, experts have advised.

In the past, desiccants have tended to be used as one product, one-shot alternatives to two or three acid sprays, sometimes with unsatisfactory results, according to Bayer CropScience.

But their effectiveness can be significantly improved by using an initial T1 spray to open up foliage, followed by a second T2 spray to complete burn down, the firm said.

Bayer suggests carefully constructed sequences of Harvest (glufosinate-ammonium), Reglone (diquat) and Spotlight (carfentrazone-ethyl) can burn down and set skins within two to three weeks.

“Reglone is a good canopy opener and very fast acting on foliage,” explained the firm’s Peter Stacey. “An initial low dose of 0.5-2.0 litres/ha is adequate to trick the crop into commencing senescence.

“Followed by Harvest at T2 five days to a week later, a controlled burn-down can be achieved that avoids shocking the crop and aggravating the risk of vascular browning.”

Harvest can also be used at T1, followed by Spotlight at T2, where conditions are too dry for Syngenta’s SMART test, he said.

While most crops will require two hits, this can be done with two chemicals, or with one chemical after flailing, commented The Arable Group’s Denis Buckley.

“Chemical after flailing is definitely making a comeback because it offers rapid haulm kill.” Theoretically flailing could spread diseases like blackleg, but he has never encountered this in practice.

Mr Buckley said there is little difference between the cost of acid-alternative chemicals, with a single pass typically costing £12-14/acre, he noted.

For the latest desiccation advice, see this week’s revitalised FARMERS WEEKLY magazine (September 9 2005).