THINK OF tennis and think of spraying potatoes for alternaria – but not this year!

Wimbledon finals week is the usual time for farmers to start thinking about treating crops for alternaria, but it is going to have its latest start since 1895, commencing on 3 July.

For potato growers who have traditionally started alternaria prevention treatments timed to coincide with Wimbers, that could be too late this season, according to Syngenta's field technical manager, Douglas Dyas.

He said this week that growers might better target treatments to the roar of the British Lions in New Zealand. The first test, on 24 June, and two subsequent Tests on the July 1 and 8, would be more appropriate to kick off alternaria spray schedules.

“All the research and experience in the UK and Europe, is that alternaria fungicide treatments have to be applied preventatively,” advised Douglas.

“That means keeping ahead of infection, and protecting crops through periods of stress when they are most susceptible to attack.”

He pointed out that this season growers have a significant advantage for disease control, with the approval for Amistar as a foliar application for alternaria.

“There is the chance to significantly extend the control window, with initial use of Amphore Plus, followed by inclusion of Amistar in the early blight programme,” he argued.

This extended prevention of alternaria, to stop early leaf senescence, could prove especially important this season on crops that have been relatively late to emerge in dry conditions and cool soils.

“We have seen that even low levels of early alternaria, which may appear to cause minimal damage, can potentially allow more virulent strains of the pathogen to attack later on and cause rapid leaf defoliation,” he warned.

Initial treatments with Amphore Plus target earlier infections of the pathogen, particularly the strain a alternata.

By applying a higher rate of 150 g/ha difenoconazole in each application, it rapidly builds up important protection – along with a full rate of mandipropamid (Revus) co-formulated in the product for late blight prevention.

“Growers and agronomists can then switch to Amistar for its proven efficacy on a solani, which testing by Syngenta and NIAB, has shown to typically come in slightly later in the season,” he added. It can be tank mixed with Revus, Shirlan and other blight fungicides for all-round protection of the green leaf.

He said growers should also take account of other risks, such as variety, soil type, irrigation, nutrition and previous history of disease, to assess the start timing to any alternaria programme – but the Lions test on June 24 would be an ideal time to take stock.

It also just happens to be the Royal Highland Show weekend!