June 7, 2013
Valuing the final wheat spray
When it comes to disease control in wheat, T3 has often been something of a poor relation. But it could be a key spray for many growers this season.
Unlike T1 and T2 applications, an ear wash may not always contribute much to yield and, in the absence of rain, may do little to help quality. As a timely top-up for foliar disease control and protection against fusarium ear blight (FEB), though, the final treatment can be invaluable. Especially so with the UK’s increasingly unsettled summers and given the devastating affect the ear disease complex had on both yields and grain quality in many cases last season.
Not only this, but the 2012 epidemic left a trail of inoculum that, under the right conditions, could cause further damaging outbreaks this season. Initial results from Crop Monitor sites in mid-May, indeed, suggest the risk of fusarium ear blight striking again is very real, especially on lighter soils.
“The experience of last season also has valuable lessons for T3 product choice,” stresses Agrii head of agronomy, Colin Lloyd, explaining that company trials work showed some of the usual contenders for the slot performed less well than expected.
“Some of the products which control fusarium relatively well are less active against the Microdochium nivale that dominated last season’s infections – on the flag leaf significantly for the first time as well as on the ears. The void they created allowed this disease to thrive. Under these conditions, Agate (prochloraz + tebuconazole) proved the best T3 option.”
While CropMonitor reports and weather at flowering will determine FEB risk and subsequent action, given the importance of topping-up T2 applications, most feed as well as milling wheat growers should be using a T3 of some description this year, Colin Lloyd believes.
“Septoria, yellow rust and brown rust could all threaten in the absence of the most timely T2 application or where susceptible varieties are being grown,” he points out
“Until last year we saw an average 0.25t/ha in extra yield from a T3 which is well worth having at current prices. In 2012, however, we gained 0.5-0.7t/ha from one well-timed spray. And don’t forget – with the true fusarium species it’s not just about yield, but also about managing mycotoxin contamination.”
Under high fusarium pressure a treatment based on prothioconazole (+ tebuconazole – Kestrel or spiroxamine – Helix) is Colin Lloyd’s first choice. Metconazole + epoxiconazole (Brutus) also provides very good activity.
He favours Kestrel or Brutus where brown rust also threatens while Helix gives the edge on ear mildew.
“Prochloraz + tebuconazole almost certainly gave valuable extra ear blight activity last season because it is more effective against Microdochium nivale than prothioconazole,” Colin notes. “But it’s worth remembering it’s not just what you pick in terms of active. Not all products are the same, with Agate also offering good protection against fusarium, septoria and rusts.
“SDHIs and strobilurins are unlikely to find a space in our T3 programmes” she adds. “Many growers will have used up their two-application seasonal allowance of SDHI – bearing in mind that Tracker is also an SDHI. And even if they could still use one, it would only really be worth it if there were a massive septoria threat. In addition, most are a bit weak on rust and have no great activity on the ear disease complex.
“Pyraclostrobin (Jenton, Tucana), in particular, offers excellent control of rusts. But strobs tend to encourage fusarium contamination of the ear because they clean off much of the background fungal population which would naturally help limit infections. In bad years, indeed, they can actually lead to an increase in mycotoxin levels.
Colin Lloyd warns that more backward crops could rush through their growth stages with some crops ending-up with boot splitting at full flag leaf emergence.
“With so much value tied up in the crop, I would still apply a robust T2-type spray here, especially on quality crops,” he advises. “If it turns wet there will be a big risk. So it may pay to come back with a low-cost late T3 ten days later.”
Whatever the timing, good application is vital. A water volume of 100 litres/ha is recommended, and adding an approved adjuvant (Kantor, Spraygard) can help spread the chemical across and around the glumes.
Low drift/fine droplet Hypro Guardian (Amistar) air nozzles or angled nozzles are good choices. Alternatively, rotating the boom tube to 45 degrees should give the correct angling of coverage with ordinary flat fan nozzles.