East Anglia: ‘Red’ risk of Sclerotinia infection as oilseed rape crops flower early

Oilseed rape growing in Suffolk.

Oilseed rape growing in Suffolk.

This year’s oilseed rape crops are up to a month ahead in their development compared with last year, with some plants flowering “super-early”, according to ADAS adviser Caroline Young.

The advanced state of the crop is due to the recent unseasonably warm weather, says Dr Young suggests ? and with it comes a significantly earlier risk of Sclerotinia fungal infection compared with spring 2013 she warns.

The ADAS risk map already shows a “red” level alert in most parts of the country, including East Anglia.

Dr Young recommends that growers in all areas should review their crop risk and plan their fungicide strategies accordingly.

“Most areas on the predictive map are now red, which agrees with what we are observing at BASF’s Sclerotinia monitoring sites, where germination has now started in all depots,” she said.

“Any crops at early or mid-flower, which are in red areas, should be considered at risk from infection and it is likely that foliar fungicide applications now may be justified. Crops in the remaining orange areas will also be at risk shortly, so fungicide treatment now will also be beneficial, assuming a three week protection window for fungicides, under normal conditions.

“Crops at late flower may also benefit from fungicide treatment; they are still at risk, but late infection tends to affect more of the lateral branches and therefore not be so damaging to yield as infection that occurs early and affects the main stems.”

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She adds that if lodging occurs, infection at any flowering phase can then spread rapidly through a crop by plant to plant spread.

In terms of timing, she advises that the main difference for growers this year, compared with 2013, is the calendar dates for early flower fungicide applications. Growers will need to be applying fungicides now, or have already applied them, rather than the more usual time of later in April or into May.

“The usual guidelines for fungicide timing according to susceptible crop stage (open flowers), inoculum risk (sclerotial germination observations and predictions, and/or petal tests) and weather conditions (warm, light rain) will still apply,“ she added.

“However 2014 conditions have seen fungicides being applied earlier, where, if no other guidelines are taken into account, oilseed rape flowering began early and continues to progress earlier than in most years. Flowering onset is variable from year to year, but, for example in most years, ADAS Herefordshire trial sites have reached yellow bud in early- to mid-April.“

BASF’s Sarah Mountford-Smith recommends that for applications targeted at Sclerotinia, growers should use Filan (boscalid) at 0.3-0.5 kg/ha, applied ideally before petal fall.

“Both Filan and prothioconazole-based fungicides give excellent control of Sclerotinia, but, importantly, HGCA trials have shown that Filan consistently contributes a yield increase in the absence of disease,” she said.

“It is also a different mode of action for resistance management of Light Leaf Spot, at a time when triazole resistant strains of Light Leaf Spot exist, and since spores will still be present in the crop. And finally, Filan is ‘Bee-safe’; it can be mixed with pyrethroids for seed weevil control at flowering when bees are not foraging.”