Continued high pressure from foliar diseases in wheat must be taken into account when making T3 fungicide decisions this season, says Syngenta field technical manager Iain Hamilton, rather than concentrating solely on ear disease.
According to Mr Hamilton, Fusarium risk often quite rightly drives T3 ear spray decisions, as well as driving the choice of triazole fungicide used as the basis of T3.
That is important given mycotoxin risks from Fusarium, he stresses. But this year, foliar pressure from Septoria tritici and in some cases Septoria nodorum, as well as yellow and brown rusts remains high depending on location and variety.
So T3 fungicide choice also needs to take account of these risks if yield and quality protection are to be adequately maintained during the critical grain-filling period, he adds.
"Remember, a T3 fungicide doesn’t just target ear diseases," says Mr Hamilton.
"It also tops up foliar disease control. Several of the foliar diseases we’re seeing this year can also move up to infect ears, if left unchecked.
"The choice of triazole fungicide should therefore take into account foliar diseases as well as activity against Fusarium and other ear diseases – for example by using a triazole which also has good rust activity where this is a concern.
"That said, a triazole alone is unlikely to give full control of all the key diseases at T3, so it is important to broaden the disease spectrum by adding other fungicide groups."
To complement the triazole spectrum, Mr Hamilton says a tank-mix with Amistar Opti (azoxystrobin + chlorothalonil) at T3 adds additional activity against late rusts, as well as the ear diseases cladosporium and glume blotch, and can extend green leaf retention.
"That is significant because loss of green leaf area to disease during grain-filling will seriously deplete yield and quality, undoing the hard work of the rest of the season.
"By contrast, a yield benefit of an extra 0.15 t/ha per day has been found from maintaining green leaf area post flowering – equivalent to 0.75 t/ha over five days."
The chlorothalonil component of Amistar Opti also provides protectant activity against the common ear disease Microdochium nivale and against Septoria, says Mr Hamilton.
Trial work confirmed that a tank mix of Amistar Opti + triazole at T3 gave better Septoria control over triazole alone and boosted yield by an extra 0.3 t/ha, worth an extra £22/ha after deducting the additional fungicide cost.
