Potato growers need to recognise that there is no single “magic bullet” solution to the loss of diquat at desiccation and, for many, it could be time for a fundamental rethink of the varieties they grow and markets they choose – particularly for those who feel they cannot flail believes agronomist Andrew Stilwell.
Andrew, who has worked for agricultural merchant Bartholomews Agri Food Limited since 2004, currently advises on 1400ha of potatoes across Hampshire and West Sussex and sees earlier agronomic planning and more selective use of varieties as the best ways forward with such a limited range of chemicals now left at grower’s disposal.
“I advise across a wide range of growers with customers targeting both the processing market and the salad sector, some will flail – some won’t (or cannot in some instances) so it all comes back to the trial work we have already done on the 2 main alternative methods of desiccation without diquat. Broadly, these are initially flailing the crop to reduce the foliage and expose the plant stems or reducing nitrogen inputs on the crop to naturally senesce the crop canopy to allow chemical to reach the plant stems more effectively. Both systems are then followed up with a stem desiccant such as Gozai (pyraflufen-ethyl) or carfentrazone from Belchim Crop Protectionto burn down the crop over a longer time period than before” he adds.
According to Andrew the biggest challenge is for those who cannot flail, either due to their soil type, or because they grow seed potatoes and are wary of greater disease risk to the crop from flailing. He forecasts that some smaller growers may simply not to be able to afford the substantial investment in a multi-bed topper or could be based in an area where there is no specialist contractor available to do the work.
“Variety selection for these “non-flail” growers will be critical given that some varieties (such as Maris Peer) have responded extremely well when we have trialled them on nitrogen rates reduced by up to 50% whereas other varieties have produced more variable results when fertiliser rates are cut back.
For growers who are able to flail finding a decent window of consistently dry weather may be their greatest challenge. From the work we have done the best results were achieved when Gozai was applied early in the morning in cooler temperatures 24-48 hours after flailing. Applying stem desiccants earlier in the day when stem pores are open and more receptive is a big plus” he continues.
In terms of performance Andrew acknowledges there is very little to choose between Gozai and carfentrazone providing both are applied in optimum conditions.
“Both are easy to apply and are effective at tackling new growth although based on my previous experience and having used both products in a variety of different conditions I would argue that Gozai deals more effectively with new leaflets that gather around the severed stems after flailing.
However, going forward in future trials I will be looking closely at the use of both products in a programmed approach with repeat applications” he concludes.