The biennial British Potato Event (BP2019) was held in Harrogate in November. Challenges from the withdrawal of crop protection products plus concerns around aphids and virus and new, aggressive blight strains, were among the principal topics of discussion.
Saltex-potential desiccant aid
Substituting diquat for desiccation is going to be difficult for growers producing indeterminate varieties such as Markies on fertile black soil, said Richard Austin Agriculture researcher Dr John Keer.
Speaking on his stand at the event, he revealed that trials this year have looked at the efficacy of Spotlight Plus (Carfentrazone-ethyl) and Gozai (Pyraflufen-ethyl), both of which are approved for use as herbicide and desiccants.
"Applied during a warm, sunny period during early September, they both worked well," he said. "However, we need to evaluate what happens when desiccation takes place later on, such as from the end of September."
After the weather broke and it became cool and dull, he found both desiccants to be slower and less effective than Reglone (diquat). "Nonetheless, mixing in Saltex – a brine using sodium chloride – improved the speed of kill. At present Saltex does not have approval for desiccation, but it can be applied as a rotational fertiliser for sugar beet later in the rotation, and thus play an important role in the overall rotational strategy."
Pelargonic acid was seen to act very quickly, but with limited effect, added Dr Keer.
"It scorches where it hits the leaf, causing desiccation in that particular spot, but, as it does not progress, the rest of the plant stays green. Additionally, the cost is currently prohibitive."
He went on to emphasise that without diquat managing and planning lifting has become more difficult. "Of course, you can still stop the crop with flailing, but it means taking heavy machinery onto the land at the end of the season, and the wheelings can make lifting difficult in heavy soils."