Autumn fungicides could boost struggling OSR

David Ellerton
David Ellerton

Extreme variations in oilseed rape establishment combined with extensive flea beetle damage in some areas and falling commodity prices pose real challenges for fungicide strategies this autumn.

But leading agronomy firm Hutchinsons says careful product selection could give a much-needed boost to ailing crops, or equally, play a key role in managing forward canopies going into winter.

“Oilseed rape development is incredibly variable this season,” says the firm’s technical development director David Ellerton. “There’s such a huge variation in crops across the country, with some yet to reach the two true leaf stage and others at eight or nine leaves.”

A lot of crops have struggled to establish in dry September seedbeds and disease is not a major concern at the moment, but he warns that high levels of background inoculum and tighter rotations mean there is a significant risk of both phoma and light leaf spot infection later this autumn.

Phoma is usually first to infect crops, but light leaf spot is the most damaging to yield and is increasingly occurring in areas where it has not traditionally been a problem, Dr Ellerton says.

“The mild, wet winter in 2013/14 meant we didn’t get the frosts to knock the disease back and resulted in leaf spotting appearing on the stems and pods later in the year. With that in mind, we could be facing quite a high-risk again this season.”

It is a view shared by West Midlands-based agronomists David Griffiths of Hutchinsons and Richard Watkins of Hodges & Moss, who say light leaf spot has become an increasing threat in western counties over the past two years.

This is partly due to reduced disease sensitivity to azole fungicides, as well as tighter rotations, says Mr Watkins, who advises growers to ideally grow rape no more than one year in four or five and to sow more disease-resistant varieties.

Mr Griffiths says many growers in his region have opted for hybrid varieties this year in an attempt to establish crops quickly and grow away from early pest and disease risk. “The conditions we’ve had so far haven’t helped establishment, but luckily we haven’t seen the same flea beetle pressure that has affected crops further east and I’m confident we’ve got the fungicide armoury to tackle any disease threats when they emerge.”

He acknowledges the cost-effectiveness of any fungicide applications will be under particular scrutiny given the downward trend for commodity prices. “It doesn’t look like we’ll be back to the days of £400/t any time soon, so we will have to be a bit careful about how much we spend this year and make sure we get the best out of products.”

Dr Ellerton advises growers to monitor disease risk carefully over coming weeks and use online tools such as the Rothamsted phoma and light leaf spot forecasts in conjunction with regular crop observations to identify the optimum spray timing and maximise the efficacy of every application. For phoma that threshold is when 10% of plants show symptoms.

The physiological effects of fungicides on canopy and root growth could be a more important driver of product choice than normal this season, he says.

For crops with average or backward growth, Dr Ellerton says it is worth considering the new penthiopyrad + picoxystrobin-based product from DuPont, which has recently been approved for use in oilseed rape.

“It’s very strong on phoma and light leaf spot and doesn’t have the growth regulatory effects of more traditional tebuconazole or metconazole-based products.

“However, early applications have been found to have a strong benefit on rooting, which could be particularly useful if crops need an extra boost going into winter. Used at half-dose, it is a fairly cost-effective option.”

Mr Watkins favours fungicide programmes based around prothioconazole for phoma and light leaf spot control, but says much will depend on disease pressure nearer the time of application. “If there’s less light leaf spot around, we might look to simpler difenoconazole-based products, or penthiopyrad + picoxystrobin where we want to increase rooting.”

Tebuconazole or metconazole-based products are likely to be more appropriate on forward crops requiring growth regulation, he notes.

“Whatever product you use, optimising disease control should be the main determinant of spray timing, with the physiological effects on growth regulation or rooting regarded as a secondary benefit. Don’t compromise disease control by trying to get these other benefits,” says Dr Ellerton.

A further option to boost struggling crops is with an early application of 30kg/ha autumn nitrogen and single, or split applications of growth-promoting products typically at the two to four-leaf stage, he adds.