Is it worth using a T0, will rust be a greater threat than septoria again, how do strobilurins fit in, and will mixing chlorothalonil cause more problems than it answers?

These are all key questions growers and their agronomists will have to tackle next spring when deciding on wheat fungicide programmes for 2008.

Keith Norman, Velcourt technical director, was adamant that the answer to the first one of those questions – is it worth using a T0 – was a resounding yes, at a recent Bayer CropScience organised fungicide meeting. “A T0 spray, around stem extension, is something we’ve always adopted – it is a good risk management tool. It pays usually four years out of five. It costs £9-10/ha. That’s church collection money compared with the down sides of not doing it.”

T0 target varied, he added. Last year it was to tackle brown or yellow rust early in other year’s septoria or, even mildew, have been worth controlling.

Responses last year were large, particularly where brown rust hit early. For example, over a 1t/ha increase was recorded in a trial on Claire in the Cotswolds from a 0.26 litres/ha dose of prothioconazole at T0, where it was followed up by two further doses of Proline at T1 and T2.

The size of response depended to a certain extent on what chemistry was used to follow up with at T1, Mr Norman admitted.

In that same trial a three-spray programme of a stronger brown rust product, Fandango [illegal in commercial practice] only gave a 0.5t/ha response to the T0 over the two-spray T1/T2 programme, for example, although yields were higher. “There is less response [from the T0] where you use more robust chemistry at T1.”

Product choice at T0 was usually chlorothalonil with or without a fast-acting older triazole, depending on the disease spectrum, rather than the more expensive triazole or strobilurin fungicides, he said.

“It is a good investment to start with a clean slate and avoid fire-fighting later. If you start with a high inoculum and it multiplies you end up having to spend more money later.”

At T1 the main targets are septoria, rusts and stem-based diseases. Brown rust was again looking very likely to be a threat, Mr Norman said. “The writing is on the wall. We’re already finding it in crops of Alchemy and Zebedee.” Only weather could stop it being a threat next spring, he believed.

Where it was a threat, using a rust-active strobilurin, such as fluoxastrobin or pyraclostrobin, in combination with an azole fungicide, was well worth considering, he suggested. But there was little point adding one if septoria was the sole focus.

Three-quarter rates of azoles should be considered the minimum at T1, whether rust or septoria was the target, he saids. “It is our default rate now. You know won’t have to come back in again before flag leaf.”

The other threat to be aware of at T1 were the stem-based diseases, especially fusarium. “Eyespot doesn’t happen every year, but fusarium does, and there is a link between what happens at T1 and what ends up on the ear.”

He backed his assertion with data from a fusarium trial in Kent, where T1 Proline, which has fusarium activity, yielded 0.6t/ha more than Opus.

The same foliar diseases – septoria and rusts – were likely to be the main threats at the flag leaf timing, Mr Norman said. Again he advocated using three-quarter rates of azoles, timed at 50% emergence of the flag leaf.

As at T1, adding a strobilurin is a good strategy where brown rust is an issue, but there isn’t a response where septoria is the only disease.

Growers also must be careful about adding chlorothalonil in curative situations. Yields were reduced from adding the product to Prosaro in trials in Dorset, where there was high pressure brown rust last season, he noted.

The T3 shouldn’t just be viewed as an ear spray, he said. “There are lots of reasons for doing it. It’s now standard practice on most Velcourt farms to offset the risk of reducing grain quality, mycotoxins, ear fusarium and as a foliar disease top-up. Proline or Fandango are good options.”

T1 caution

Perhaps controversially, Mr Norman was less keen on tank-mixing chlorothalonil at T1 than some other advisers. “Chlorothalonil’s price is likely to go up, and there is no point putting anything in unless it is going to give you a return.

“Technically, putting a bit of Bravo in is not always the right thing to do either – you need to be aware of antagonism with azole fungicides. Chlorothalonil can interfere if you’re looking for the triazole to work curatively.”

He also remained to be convinced about the use of prochloraz at T1 for the control of septoria. Ongoing research has found that prochloraz has significantly more effect on one particular septoria mutation than other azole fungicides. But whether that information could be used to practically help control septoria more effectively was unproven, he believed. “Prochloraz mixes haven’t brought anything in trials yet.”

That could have been because it wasn’t a severe septoria year last season or because the mutation was not that dominant yet, he noted.