Early fungicide is needed but what product to use?
Agronomists are unanimous about the benefits of a T0 fungicide this spring, but opinions on whether to use a curative (triazole), preventative (chlorothalonil) or combined approach are somewhat more divided.
For most wheats a triazole will not be needed, according to Bill Clark of ADAS. “Septoria is the number one target at T0 and the easiest option is one litre of straight Bravo [chlorothalonil].
“The mild conditions have really got the septoria going, so at T0 you’re unlikely to have any leaves that won’t be infected. You can’t eradicate infection that’s already there, so the only thing you’re doing is to protect against future disease.”
Where yellow rust is a concern, Mr Clark says there may be some justification for including a triazole, but the risk is very low and growers can afford to wait until T1 to control it.
But Lincolnshire AICC agronomist Ruth East says that the large amount of rust-susceptible wheat varieties in the ground means triazoles cannot be overlooked at T0. “We’ve got a lot of brown rust in Alchemy and saw some yellow rust before Christmas in Robigus. Septoria is there, but I think you should deal with it at growth stage 31-32.” She prefers a triazole mix at T0, saving Bravo until T1.
Growers should not be tempted to use primary azoles, such as Proline (prothioconazole), at the T0 timing, says Bayer CropScience’s Nigel Godley. Saving the product until T1 is more effective and a better pesticide stewardship option, he explains.
“At the T0 timing the main focus is septoria and all you are really looking to do is damp it down until T1. There are plenty of options for doing this without the need to call upon Proline.”
Whatever T0 product is being used, ProCam’s David Ellerton says it is important to consider what impact its timing will have on the interval to T1 and not spray too early. Ideally, all spray intervals should be less than four weeks, he says. Latest figures from the firm’s 4cast survey indicate intervals over four weeks reduced yields by 0.31t/ha in 2006.
Mr Ellerton recommends applying T0s in the third week of March, basing them around chlorothalonil or mancozeb as protectants. He thinks triazoles have a role, particularly where brown rust is bad on varieties such as Alchemy.
Eyespot
“The exception is prothioconazole, which has a weakness against brown rust,” he notes. “Prochloraz may be worth including if you’ve got second wheats with bad eyespot. It also has the potential to make T1 sprays more effective as there is evidence it is active against mutated septoria strains.”
Where growers opt to use a triazole, increasing resistance problems mean that rates should not be cut back, he adds. The 4cast survey shows that septoria control from half doses has declined from 90% to 50% over the past 10 years, while at the same time many growers have cut rates back from 80% to approximately 50%.
T0 key points
Q Strong case for T0 this season
Q Septoria main target
Q Triazoles may be needed against rusts
Q Focus on preventative rather than curative action
Q Keep spray intervals below four weeks
