Farmers thoughts will be turning to T1 and T2 decisions over the forthcoming weeks
With the vast majority of T0 fungicide applications on wheat completed, farmers and agronomists’ thoughts will be turning to T1 and T2 decisions over the forthcoming days and weeks. Dominic Kilburn seeks advice on these key fungicide timings.
There’s been a false sense of security when it comes to disease control in cereals. The warning bells sounded in 2012, and again last year when high levels of septoria inoculum in wheat reminded us that there has been a significant sensitivity shift to triazoles in the field.
That’s according to Syngenta field technical manager Iain Hamilton who warns that the shift in sensitivity is starting to bite and our ability to manage disease as we used to has changed.
He says that most products available for wheat fungicide programmes now primarily offer disease protection, rather than being curative; in the past when disease had got into the crop the situation could often be retrieved at the flag leaf (T2) timing, now it cannot be rectified.
“Our view is that it’s becoming increasingly unlikely to cure established Septoria in wheat and so we have to look very carefully at fungicide programmes to tackle this,” says Mr Hamilton. “We need to do more up front, earlier in the programme, to keep on top of disease and to reduce the risk of finding ourselves in a curative situation.
“Previously, spend on fungicides was favoured 60/40 towards T2 applications at flag leaf, compared with the T1 timing, but we reckon that spend should be equally split on both,” he added.
Timing of the T1 application is very important, continues Mr Hamilton, reminding growers that leaf 3 should be three-quarters out. “Typically this is at growth stage 32 although this could be earlier or later, depending on sowing date and growing conditions for example.
“What is key is that timings are not based on calendar date and that the interval between T1 and T2 is not stretched – 3-4 weeks at most,” he points out.
Assuming a robust T0 has been applied, and to get the ‘up front’ protection needed at T1, Mr Hamilton suggests that a three-pronged attack of an SDHI and triazole – Keystone (epoxiconazole + isopyrazam) + Bravo (chlorothalonil) is required to keep the threat of septoria and rust at bay.
“When you make the decisions regarding T1, you don’t know what conditions in the field are going to be like thereafter, and it doesn’t take much wet weather to spread septoria. So get the foundations right at T1 with a robust application and then tailor T2 when you get there, and not the other way around,” he explains, adding that isopyrazam (the active in Keystone) has shown to be the most persistent of the SDHIs in trials compared on a #/ha spend basis. A minimum of 75 per cent rate SDHI should be used (0.75-litres/ha Keystone).
Flag leafAssuming the foundations for good disease prevention have been set at T1, then the flag leaf spray at T2 should be relatively straight forward, continues Mr Hamilton. “The difference between SDHI performances at the flag leaf spray, as part of a full programme, are minimal and so the same three-pronged approach used at T1 can be repeated here, tailoring rates according to disease pressure. If it stays dry then rates can be adjusted accordingly and possibly the Bravo left out.
“If yellow rust has re-infected, adding in a strobilurin such as Amistar will help with control,” he adds.
“However, should T1 timing be compromised and septoria re-establish in the crop, then full rates should be used, but it is likely that some yield will already be compromised due to the lack of curative control available,” he concludes.
Tweak rates accordinglyT1 80 per cent of full rateT2 80-100 per cent of full rate, tailoring it to the situation