Crop growth stage key to potato blight success

Potato growers must time blight fungicides carefully to kick in during specific crop-growth stages if they are to combat more aggressive strains, experts have warned.

Fungicide programmes should be targeted at two growing phases, said Bayer CropScience product manager Neil Thompson.

Best times were the "rapid-growth phase" or the "stable canopy phase", and using products to suit these times could make a big difference to blight control.

"During rapid canopy growth, when the crop is building new stem and leaf tissue daily, it needs systemic protection," Thompson said.

"Phenylamide and propamocarb-based fungicides are the only types listed in the Euroblight table as providing systemic mobility. But all the testing of Blue 13 isolates in Europe so far have shown resistance to phenylamide chemistry."

Propamocarb-based fungicides were unaffected by this. So Consento, Merlin, Prompto or Tattoo offered reliable systemic protection during rapid canopy growth.

When the canopy is almost complete and crops are starting to flower and initiate tubers it is time to switch to products with tuber-blight activity, said Thompson.

Tuber blight is caused by rain - or irrigation-washed spores from leaves and stems hitting the soil, he said. Fungicides needed to blitz them before they reached the soil.

"The combination of fluopicolide and propamocarb in Infinito provides the strong anti-sporulant activity needed.

"Under high blight pressure, moving to a block of three Infinito sprays will build up a solid foundation of tuber protection. Once the maximum total dose of 6.4 litres/ha per crop has been used up, switch to other products with tuber blight activity to complete the programme," he advised.

For Blue 13, Thompson recommended using Infinito at 1.6 litres/ha from canopy complete onwards.

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