Decide on T0 fungicides on a crop-by-crop basis

Crop development and variety choice should dictate whether T0 sprays are applied in the coming weeks, agronomists say.


For most growers the decision will need to be on a crop-by-crop basis, Steve Harrison, an independent agronomist from Somerset, says.


Don’t lose sight of what needs to be achieved, he stresses. “The T0 is optional – a prescriptive approach won’t be appropriate this year.”


Some thick and leafy crops will need spraying, he points out, but plenty of others won’t. “Those that are forward enough by early April will benefit. But they won’t show a massive yield response.”


The aim is to get the fungicide onto leaf 4, he explains. “And if you’re combining it with a PGR, crops must be at GS30/31 for best results. But many are still tillering; stem extension is some way off.”


Over-wintered septoria can be found on old leaves, but brown rust is absent except on the winter barley varieties, Sequel and Saffron, reports Mr Harrison. “And there’s mildew in the winter malting barley variety, Cassata.”


Where an early spray is deemed necessary, chlorothalonil is his choice for septoria. If rust control is required as well, he suggests adding a triazole. For mildew, either a triazole or metrafenone can be used.


“Fungicide prices have gone up by 15%, which is the biggest single increase for some years. But there are still some reasonable buys out there – some of the co-formulations look very cost-effective.”


Once the later drilled crops start to grow, they will be very prone to mildew, he warns. “Those on slumped or capped land will be short of manganese, which makes mildew worse. This is where Flexity (metrafenone) or Talius (proquinazid) have a place.”


AICC chairman Andrew Watson in Norfolk will also be advising a T0 for early drilled wheats, but can’t see a requirement to treat the more backwards crops.


“These later wheats will go through the growth stages very quickly, bringing the T0 and T1 timings very close together and making it hard to justify the first spray.


“Also, there’s no need to split the chlormequat application with backwards crops. So the growth regulator can go in with the T1.”


Temperatures have been too cold for disease to develop, says Mr Watson. “Septoria is there, as is mildew in places. But there’s nothing out of the ordinary.”


He also favours chlorothalonil or low rates of Cherokee (propiconazole + cyproconazole + chlorothalonil) where a T0 will be applied.


Mark Hemmant of Agrovista points out that although the disease risk may be lower with late drilled crops, the impact of any disease is greater. “In crops with a smaller canopy, the lower leaves contribute more. They’re also more prone to mildew.”


Where a T0 isn’t planned, the timing of the T1 will have to be spot on, he adds. “Growers might end up adding what should have gone on at T0 to the T1 spray, so they might not save any money.”


He agrees septoria and mildew are the main threats, but reminds Robigus growers about yellow rust.


In Scotland, the need for a T0 on certain varieties is stronger than ever, says Fiona Burnett of SAC.


“Yellow rust has not objected to the cold winter. It’s present in Robigus and will need treating at GS30 with a low dose of triazole.”


The same is true of septoria in Consort, she reports.


In contrast, brown rust hasn’t enjoyed the cold. “So there’s less need for a T0 spray in Alchemy this season.”


Mildew and septoria key issues

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