September 26, 2013
Two Spray Autumn Fungicide Programmes Advised for Optimum OSR Managment
Variable but generally forward crops, high light leaf spot risk levels across much of the country and a relatively late phoma season make two-spray autumn fungicide programmes carefully matched to crop development important for most winter oilseed rape growers this season, suggests Agrii regional technical adviser, Will Foss.
“Last year our testing of a wide range of autumn programmes showed responses of up to 0.7t/ha from a two spray sequence,” he explained. “And over the past eight years we’ve seen typical autumn/winter fungicide responses across varieties and treatments of between 0.25-0.5t/ha. So it’s clear that autumn sprays pay dividends regardless of the season.
“It’s equally clear from our work, though, that they pay dividends for different reasons in different seasons. Last year’s small, late emerging crops and high early phoma risk, for instance, put the premium on robust disease control.
“But this year we’re looking at many well-established crops at 6-8 true leaves at the end of September that could use some decent early growth regulation. While less early phoma takes the pressure off curative disease management, we have noticeably higher light leaf spot forecasts for most regions and continued late phoma development concerns.”
“Add to this the fact that dry initial seedbeds in many areas delayed germination and emergence, leaving crops at a range of growth stages, and the extra flexibility of two-spray autumn programmes will be particularly valuable this season.”
With forward, well-established 4-6 leaf+ crops, Will Foss recommends initial treatment with metconazole for its superior growth regulatory effect – especially where a combination of reasonably high seed rates and good establishment has meant relatively thick crops. For the best effect, it needs to be applied to active growth during the early part of the season, which is likely to mean spraying before the 10% phoma threshold in many cases.
For crops at the 2-4 leaf stage at first treatment, he advises a lower rate of metconazole initially, combined with a prothioconazole/tebuconazole mix or fluzilazole to give good disease management with some PGR activity. Alternatively, a tebuconazole/prochloraz combination.
On smaller crops where early growth regulation is of less importance, he suggests using prothioconazole with lower rate tebuconazole or a fluzilazole-based spray initially.
“In each case, I’d follow-up these treatments with a combination of prothioconazole + tebuconazole 4-6 weeks later or at disease re-infection to target light leaf spot and phoma,” Will Foss said. “And where further growth regulation is desirable I’d choose products with higher rates of tebuconazole.
“The extra flexibility of a two spray programme is especially valuable in a season like this with crops at different growth stages and requiring different levels of growth regulation. We have also found both fungicidal and PGR activity can be enhanced by including an adjuvant like Kantor.
“While thresholds provide valuable guidance, in practice autumn fungicide timings often depend on when the sprayer is travelling to apply other treatments,” he stressed. “This makes it important not to miss application opportunities – even if they seem rather early – in case weather conditions get in the way of further spraying. It also makes it vital to be aware of the incompatibility of some products with Crawler (carbetamide).”