Potato growers are on high alert for blight infections but, so far, crops are reported as being blight-free.
The hot, humid weather had brought the first real challenge of the season, with the next five to seven days crucial, said Barrie Florendine, UAP's potato specialist.
Up to this point the season had been relatively straightforward with low levels of blight risk allowing some growers to cut costs. "But now is the time to be spending a little more. I'm reaching for the better quality products, such as Ranman, Revus, Valbon and Infinito."
Norfolk grower Tony Bambridge hadn't seen any blight in his crops yet. "It is perhaps a little surprising as we've had the conditions to think it should be there," he said. "Perhaps 'blue-13' doesn't want to party this season!"
A more likely explanation was that while humidity levels had increased in the recent hot weather, there hadn't been any prolonged leaf wetness at the same time, AgroChemex's John Keer said.
"That's a very big factor - you need both humidity and [blight] outbreaks to get things going, and we haven't had many outbreaks. There is usually enough inoculum floating around, but you need to have prolonged leaf wetness to allow the spores to germinate," he explained.
It meant growers needed to watch out for misty or dewy mornings in the current hot spell to really ramp up blight pressure, he said. "If we get high temperatures without the mists in the morning then pressure will remain low, and there is the potential to save money by using some of the older products."
In Herefordshire, Russell Price's 400ha (1000 acres) of crops that he was responsible for blight control on, were also blight-free. "We haven't seen any signs of blight yet, but it might start to rear its ugly head this week if it stays as humid as it is," he feared.
"We're on high alert and are tightening our spray intervals to seven days again. After the last two years there is an element of paranoia."
Mr Bambridge was also employing a seven-day programme to minimise the risk of weather delays letting blight in to crops. "Our 600 acres is spread about so it takes four or five days to get around. With any weather delays we can quickly get to eight or nine-day intervals," he explained. Similar delays to a 10-day interval programme would lead to unacceptable risks for blight control.
He was also moving to more robust, curative products. "With this kind of pressure we need to make sure we don't miss any small foci of blight. There is still a lot of fresh growth that needs a robust programme."
Where rainfastness was a priority, Ranman and Revus were the best choices, Mr Florendine noted. "Last year showed us that you could expect virtually full activity just 20 minutes after spraying even it rained."
In contrast, rain after Infinito could leave growers "a touch exposed", particularly if the leaf was damp at application, he said.
Active ingredients
- Ranman - cyazofamid
- Revus - mandipropamid
- Infinito - fluopicolide + propamocarb
- Fubol Gold - mancozeb + metalaxyl-M
- Valbon - benthiavalicarb + mancozeb