Risk forecast to guide sclerotinia spray decisions

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Regular sclerotinia forecasts for oilseed rape (OSR), which flag up when the crop is at risk from infection, are available from the AHDB website.

Based on actual and forecast weather, the map-based tool indicates the infection risk level at 15 sites. The information can be used to focus monitoring efforts and guide the application of protectant fungicide treatments to prevent or limit infection during flowering.

AHDB has published forecast infection risk information since 2015. The 15 sites used in the 2018 forecasts stretch from South West England to the Scottish Borders.

OSR is at the highest risk of infection when relative humidity is greater than 80 per cent and temperatures are at or above seven degrees Celsius for more than 23 hours. A simple traffic-light system is used to indicate the infection risk level at each site:

  • Green = less than 21 hours of continuous infection conditions
  • Amber = 21 to 23 hours of continuous infection conditions
  • Red = 23 hours or more of continuous infection conditions

The forecasts are updated three times each week (Monday, Wednesday and Thursday).

Caroline Young, who works on the forecasts at ADAS, said: “Infection risk information is vital for the control of sclerotinia, as fungicides have little or no curative activity and should be applied ahead of infection.

“The forecasts show if there’s been an infection alert in the previous 24 hours or if there’s likely to be an infection alert in the next 48 hours.

“If spores are present, they can germinate and infect for a day or so after an alert. So, if a spray can’t be applied in time, it should still be applied as soon as possible after the infection alert because there will still be a benefit, albeit a diminishing one.”

Commentary will also be published on the site to pull out key trends and regional hotspots. Information on other key risk factors – including crop growth stage, spore pressures, sclerotial germination progress and results from petal tests – will also be presented, when possible. Information on disease pressure is particularly important, as an infection alert only counts if spores are present.

Forecast information can be accessed via cereals.ahdb.org.uk/sclerotinia

Fungicide performance

Optimum timing for a single spray is usually just before mid-flowering on the main raceme and prior to significant petal fall. As treatments provide good control for about three weeks, two sprays may be required to protect crops at high risk sites throughout the flowering period and when the flowering period is extended.

Independent information on fungicide performance is published on the AHDB website at cereals.ahdb.org.uk/fungicide

AHDB is also working with the Crop Health and Protection Centre (CHAP) to provide long-term pest and disease forecasts for wheat, barley, OSR and potatoes.


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