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Variable growth poses autumn OSR fungicide challenge - David Ellerton - Farmers Guardian

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Early disease pressure in oilseed rape is much lower than last year as a result of the dry conditions during August and early September.  However, variable growth is set to complicate autumn spray decisions, growers are advised.

By the end of September, early sown forward crops in many areas had reached the fourth true leaf stage, while the most backward crops were only just emerging, according to agronomy firm Hutchinsons.

Robert Barker, Yorkshire-based agronomist with the firm, says: “The differences in this region are largely moisture-related.  There are some crops on the Wolds that did not receive rain early in the season and then also got hit by flea beetle, so really struggled to get going.  Equally, we have got other crops in areas that caught rain showers after drilling or were direct drilled to conserve moisture that established well and look much better.  It is a very variable picture, but at least disease pressure is generally pretty low.”

There is a similar picture elsewhere in the country, according to Hutchinsons technical development director Dr David Ellerton.

“Last year we had already seen plenty of phoma incidence in crops by late September and early October, whereas disease pressure so far in most places has been much lower”.

Disease risk

However, given recent heavy rain and very variable growth stages, advice to growers is to monitor disease risk closely and tailor fungicide programmes to in-field risk, variety susceptibility and growth stage, says Dr Ellerton.

With later disease development than last year, some growers may well be able to use a single well-timed fungicide spray to protect crops from phoma and light leaf spot through winter, he adds.

“Generally speaking, the optimum time for a single spray is late October or early November, however accurate timing is everything.

“If you spray too early, fungicide activity may run out of steam if phoma comes in late.  In contrast, you cannot afford to delay too long and risk disease getting established in the crop.”