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A sclerotinia risk alert service has been launched to help oilseed rape growers better target spray programmes.

A sclerotinia risk alert service has been launched to help oilseed rape growers better target spray programmes.

Based on observed and forecast weather data, the service keeps growers informed of potential sclerotinia infection risk periods.

This helps focus in-field monitoring as oilseed rape enters its critical flowering period.

Launched by the Agriculture & Horticulture Development Board, the service features a web page which includes inoculum-pressure data from a limited network of spore traps and information on crop growth stages.

Analysis of last year’s results showed that the sclerotinia forecasts were about 96% accurate, with only around 2% false negatives, says Catherine Harries, who manages disease research at the AHDB.

Encouraging results

“Forecasts are never perfect, but we are encouraged by the results. Information on the presence of spores, weather and crop growth stage can really help target sclerotinia sprays.”

Decisions based on sclerotinia inoculum levels and weather-based infection risk resulted in 26% fewer crops needing treatment last season – helping growers to increase margins, according to AHDB-funded research.

Typically, the optimum time for a single spray is just before mid-flowering on the main raceme. Since fungicides have protectant activity, this spray should be applied prior to an infection risk alert.

Persistence of full-dose fungicides is approximately three weeks, says the AHDB. If a spray is made earlier – or if the flowering period is extended – a second spray may be required under conducive infection conditions.

Leaf spot and aphids

Meanwhile, the AHDB has updated its light leaf spot forecast after a relatively wet winter showed a large jump in oilseed rape disease risk. This tallies with field reports suggesting light leaf spot infection is most evident on susceptible varieties.

The increase in risk – compared with a preliminary forecast last autumn – is generally larger at locations further away from south-east England. Lower winter temperatures mean aphids are likely to take flight a little later than average this spring.

The annually updated forecasts, produced by the Rothamsted Research Insect Survey, suggest aphids will fly about two or three weeks later in Scotland and northern England – and up to one week later than average over much of the rest of England.

To access the sclerotinia risk alert service, visit ahdb.org.uk/sclerotinia