Cuttingcorners to save a few pounds on the crucial flag leaf spray timing is anunnecessary risk that could jeopardise wheat yields more than ever this season,leading agronomy firm Hutchinsons warns.
Diseasepressure, particularly Septoria and yellow rust, has been exceptionally highthroughout this season and many crops have excellent yield potential that needsprotecting through to harvest, the firms technical development director DavidEllerton says.
Even ifearlier T0 and T1 sprays went on in good conditions at the optimum timing, DrEllerton warns there is still no reason to cut costs at T2 (growth stage 39),which risks undoing the earlier hard work and compromising yield.
Get the T2spray wrong and youre in trouble. Weve seen in previous years how quicklythings can go wrong when the weather changes. Spring 2012 was a classic exampleof that, but then we were starting from a relatively low disease base after aprolonged dry spell. This year weve got a lot of forward, lush crops and ahigh level of disease already, so pressure on the flag leaf could be enormousgiven the right conditions.
Awell-timed robust T2 spray based on SDHI chemistry, combined with anappropriate triazole is the perfect insurance policy to deliver strongcurative disease control and keep the yield-building flag leaf as clean aspossible, Dr Ellerton advises.
Anyadditional cost from such an approach is outweighed by the extra curative andprotectant activity that SDHI chemistry delivers over traditional triazole/strobilurin strategies, he says.
Ideallythe flag leaf should be almost fully emerged to get decent spray coverage, butit is possible to go slightly earlier when its at least half emerged if necessary.The last thing you ever want to do is delay T2 and have the flag leaf out forany length of time with no protection.
There are anumber of excellent broad spectrum pre – formulated SDHI + triazole productsavailable for use on the flag leaf. However straight SDHI formulations may alsobe mixed with triazole based products giving growers greater flexibility. Mixedtriazole products based on epoxiconazole or prothioconazole offer advantagesover straight triazoles in terms of efficacy, he says.
An effectivedose of SDHI should be used, although Dr Ellerton acknowledges the definitionof this varies between products. Rates should be adjusted, depending on diseasepressure and level of curative activity required. However even the latest SDHIsdont have the same curative ability on Septoria that triazoles had in themid-90s, so youve got to watch crop growth stages closely and be prepared toact promptly before the disease becomes established on the upper leaves.
Bridge thegap to T2
With the T2fungicide likely to be going on around the usual time of the second to thirdweek in May, Essex-based Farmacy agronomist Andrew Spackman believes it may beworth applying an intermediary spray between T1 and T2 in forward crops wherethe interval is likely to be close or beyond the maximum four weeks.
Anyone whoapplied their T1 in the first couple of weeks in April should consider going inwith a triazole plus chlorothalonil mix as a holding spray around three weekslater if they think the gap to T2 is going to be stretched too far, he says.
Youllprobably end up going back on with the T2 quite soon after the intermediaryspray, but its a relatively cheap solution that helps to extend the protectionof leaf two and three and reduce pressure on the flag leaf spray if diseasepressure is high.
Mr Spackmansays it is vital to watch how disease pressure develops closer to flag leafemergence and be prepared to tweak tank mix partners and dose ratesaccordingly.
Septoriais the biggest driver of fungicide choice this year, but dont write off otherdiseases too, especially rusts. There was a lot of yellow rust in crops duringthe winter and although that seemed to have abated in the early part of theseason, the inoculum was still present on lower leaves in many crops and builtrapidly in some varieties during the stem extension phase. Brown rust too couldbecome a concern if we see dry and warm weather over the coming weeks.
Aggressivenew races of yellow rust, such as the Warrior strain, can build up very quicklyand have the potential to overcome varietal resistance, so any crop ispotentially at risk, adds Dr Ellerton.
The worstthing you can do is end up in a situation where youre trying to get on top oframpant yellow rust, particularly if the weather goes against you and you cantget on in the early stages of infection.
Dr Ellertonsays barley crops also have good yield potential this season and SDHI chemistryplus a good triazole or cyprodinil should form the basis of any T2 programme.
All of thenew SDHIs have a strong place at T2 in barley, although rates tend to be lowerthan at the T1 timing, he says.
Theres afair amount of brown rust around at the moment and also net blotch andrhynchosporium where conditions are wetter. Its also worth bearing Ramulariacontrol in mind at the T2 timing.