With the last potato harvesting season when diquat can be used for desiccation upon us, attentions were turning to possible alternatives at Potatoes in Practice, near Dundee.
Focusing on high grade seed crops, Greg Dawson of Scottish Agronomy said rapid haulm death is important to minimise fungal pathogens and regrowth could increase the risk of virus.
Mr Dawson said that chemicals such as pelargonic acid could enter the desiccation market
In terms of flailing, he said it could sometimes be difficult to keep chop length to 20-25cm to avoid damage to tubers. Root cutting is also an option, however, bacteria can enter the roots, he added. In wet conditions, flailing and root cutting may damage potatoes and spread blight, for example, highlighting the importance of chemical options, said Mr Dawson.
“Canopies can be taken down using chemicals only, for example [a grower used] one litre of Spotlight then 0.6 litres a week later. Haulm death was slower but we got to the same point. The sunshine helped last year but it may not be so good in the rain. The grower felt stolon detachment was better than going through with flails.
“I have reservations about it as if haulm death is slow there is more risk of fungal infections.”
Also looking at the implications of loss of diquat was Agrii, which had a trial plot at Potatoes in Practice.
The treatments looked at use of diquat, Gozai (pyraflufen) and Spotlight Plus (carfentrazone) with and without flailing (pulverisation).
Agrii agronomist Andrew Sprint said: “Gozai and Spotlight are not good at killing mature leaf. You have to pulverise to get results. The alternative desiccants [to diquat] are so slow. Applying four times, for example would be slow and very expensive.”
From the trial results he recommended 0.8l/ha of Gozai with 1.5l/ha of Toil adjuvant then waiting 5-7 days to flail the crop. “Then 1-2 days later potentially follow up with 0.8l/ha of Gozai with 1.5l/ha Toil or 1l/ha of Spotlight Plus,” he added.
Andy Steven, agronomist at Agrovista says if topping is possible and the conditions are right that this is the default option.
“Top, then apply either a litre of Spotlight or 0.8l/ha of Gozai - keep the water volumes up. Growers have a decision: if they have masses of acres to cover they will want to go at lower water volumes but you won’t get the same coverage. I wouldn’t go much more than 300l/ha.
“We have growers doing 200l/ha and if they have a good sprayer set up it works fine. Angling the nozzles helps too; you don’t have any down side to doing it. It helps your blight spray too. I would recommend angled nozzles for the whole programme, from start to finish, including the weeds. An angled nozzle alternated with a flat nozzle all the way along the boom.”
Indeterminate varieties and vigorous, over-fertilised varieties will need much more planning, he says.
“If you apply too much nitrogen, it has consequences; it will be harder to burn down and it will take longer to skin set. Growers like the idea of one fertiliser at one rate and crack on but you can’t do that.”