Hot humid conditions raise blight risk

Recent heavy rain showers onto warm soils will quickly create hot and humid conditions that are highly conducive to blight, according to Syngenta Potato Fungicides Manager, Stephen Williams. As soon as crops reach a stage of touching between rows growers must ensure they are using a highly robust fungicide programme and maintaining spray intervals, he advises.

Mr Williams highlights that humidity within the covered crop can quickly rise following any rain or irrigation, resulting in infections on stems and lower leaves even when top leaves are dry. After the dry weather crops have been waiting to get away; the soft growth of rapidly expanding leaves are especially susceptible to blight infection, he warns.

He advocates growers incorporate the leading blight fungicide, Revus, into the programme during the period of rapid canopy growth. Revus is recognised by independent trials as the top fungicide for protecting against leaf blight. Importantly, the protection will move with expanding leaf growth, ensuring exceptional levels of blight control between applications.

It also has outstanding rainfastness, which could prove invaluable during showery early-summer weather, said Mr Williams. He adds that operators welcome the very easy to use formulation and the new Syngenta S-pac packing, which is quick to open and easy to rinse, ensuring high sprayer output to cover more hectares per day.

Mr Williams warns that even if development of any early infection can be held by a comprehensive blight programme, it will be storing up problems and increasing risk for later in the season. It is imperative that growers and agronomists invest in the best possible early season programme, he advised.

Ruairidh Bain of SAC calculates an early foliar blight attack will incur extra costs from additional blight fungicides designed to dry up lesions and stop its spread – typically two extra sprays in the programme at a cost of over 80/ha including application. Crops in surrounding fields within a half mile radius will also require an upgrade in fungicide selection to offer greater protection.

SAC also estimates crops will incur a 5t/ha yield penalty where haulm destruction is required two weeks ahead of schedule as a result of blight, typically incurring a cost of around 650/ha. The consequence of lifting blight infected tubers, however, could be far worse with additional store losses and grading costs, he adds.

Growers and agronomists can receive a free five-day forecast of blight risk for their farms on the Syngenta website, www.syngenta-crop.co.uk The BlightCast service enables growers to be more proactive with spray scheduling and product selection, to optimise season-long blight control programmes.

 

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