Changing weather conditions heaps blight pressure on potato growers

Farmers are facing challenging conditions in which to control late blight after Hutton Criteria disease warnings were declared in key potato-growing areas.

A large percentage of the UK crop is at the critical rapid canopy growth stage and in need of robust protection but heavy rain and waterlogged soils in some areas means it may not be possible to apply protective sprays in a timely fashion.

Temperature and humidity in the past week have sparked red warnings – indicating the highest level of blight threat – in many counties including East Anglia, the south and west of England and as far north as East Yorkshire.

Corteva Agriscience advises that current conditions will lead to product choice and application timing taking on even more importance.

The crop protection and seed company’s field technical manager Craig Chisholm says growers should consider the length of protection they need and whether their chosen blight spray has any curative properties.

Corteva Agriscience Field Technical Manager, Craig Chisholm

Craig said: “The potential for a high blight pressure year was already present due to the increase in volunteer potatoes across the rotation, coupled with the mild winter. Dry conditions and recent cooler temperatures kept a lid on it.

“But the deluge of rain we’ve witnessed and rising temperatures triggered warnings across many key potato areas. Growers will be particularly concerned about this as many crops are at rapid canopy stage and need protection of vulnerable new growth.”

Where sprays have been postponed by the conditions, a product with some curative activity will help tackle any blight infection already developing in the crop.

Craig said: “Choosing an active ingredient with curative properties will ensure growers claw back some of the days of lost protection.”

Flexibility on timing future sprays is also part of the conundrum.

“The efficacy of most blight sprays burns out after seven days which will be a problem if the wet and windy weather persists and sprayers can’t get on the field.

“By including a molecule such as oxathiapiprolin (Zorvec) in a programme, growers will be better able to cope with inclement weather as the 10-day spray interval provides flexibility for growers.

“Under high blight pressure when agronomists would generally be looking at reducing spray intervals to five days, the robustness of oxathiapiprolin will enable growers to stick with their seven-day schedule, enabling crop coverage to be maintained.”