Eleventh hour warning for urgent T2 sprays…
By Andrew Swallow
SOARING septoria pressure in wheat is threatening to decimate yields yet many growers havent woken up to the risk, warns one leading scientist. In many cases beefed up flag-leaf sprays need to be applied as soon as weather will allow.
"There is a real need for a sense of urgency with sprays this season which I am afraid is missing on many farms," warns ADASs Bill Clark.
"Despite all the dry weather we had the disease pressure is still high in most crops. There is a lot of disease on leaf four and even on leaf three and the flag leaf and leaf two are in amongst that inoculum. It is almost sure to be infected."
Traditionally, the ideal timing for the flag leaf spray is GS39, flag leaf fully emerged on the main tiller. Most wheats in East Anglia will be approaching that next week but in many cases too much haste earlier in the season means crops should be treated as soon as possible.
"If it is more than three weeks since the last fungicide was applied you need to get on – even if the flag leaf is not out," he stresses.
In such a situation picoxystrobin (as in Acanto) or trifloxystrobin (as in Twist) should be used as the strobilurin component of the mix because of their ability to redistribute themselves and protect new growth.
Alternatively a quarter-rate of a triazole such as Folicur (tebuconazole) could be used as a holding spray until the flag leaf emerges, he says.
Where T1 sprays were well timed and robust, leaves three and four should have been protected and so still be clean. Here, growers can probably wait for full flag leaf emergence and the balance of product choice moves to pyraclostrobin (as in Opera) or Landmark (kresoxim-methyl + epoxiconazole).
Partner triazole rates should be tuned to variety resistance. In practice observation of disease on leaf three and four will do that automatically.
"On a variety like Claire you are less likely to see septoria on these leaves, so the flag leaf and leaf two should be clean. You could cut back from a three-quarter to a half-rate with the triazole." *
Most wheat in Scotland is approaching GS37 with leaf two fully out, says SACs Simon Oxley. Where early fungicides were applied at GS32, perhaps following a "T0" spray too, he says growers should wait for full flag leaf emergence and give winter barley T2 and spring barley T1 sprays priority. "There is a real rhynchosporium risk. Get on in winter barley when the awns are peeping. Once the heads are out the leaves are very hard to hit." Mildew in spring barley should be hit with a morpholine, he adds. "We anticipate it will be resistant to strobilurins."
• Check leaves 3&4 for septoria.
• If infected spray ASAP.
• If clean wait for full flag.
• Septoria pressure extremely high.