Beware delays to wheat crop flag leaf applications

12 May 2000

Beware delays to wheat crop flag leaf applications

By Andrew Swallow

FORWARD wheats were at flag leaf emergence as far north as Yorkshire earlier this week.

On most crops disease pressure remains high, and delaying flag leaf applications beyond GS39 would be risky, say agronomists.

In East Anglia, most wheat is at GS33, forward crops at GS37, and some Soissons has the flag leaf fully out already, says ProCam technical director, David Ellerton.

Most growers got sprayed up with T1 applications last week, but that does not mean flag leaf applications can be delayed. "Growers could be tempted to delay until the ear is out, but that would be wrong. The flag leaf is the critical timing."

Herts/Essex-based independent agronomist Peter Taylor echoes his comments. "I would not want to leave it any longer than full-flag leaf emergence," he says.

On rust or septoria susceptible varieties he recommends Amistar (azoxystrobin) or Twist (trifloxystrobin) respectively, mixed with a modern triazole. But a half-rate of Landmark (epoxiconazole + kresoxim-methyl) costing growers £17-20/ha (£7-8/acre) will be more economic on generally disease resistant varieties such as Claire or Malacca, he says.

"You do not want to overspend on the less responsive varieties."

Hampshire Arable Systems agronomist Stephen Cook says wheats in his Hants/Berks/Surrey area are just reaching flag leaf.

Delayed T1 applications mean growers can afford to wait until the flag-leaf is fully emerged before spraying, but no later. "And if the T1 went on in March it will need to be at GS37."

Twist, with a likely £2-£3/ha cost over other strobilurin choices, is worth trying on at least a field or two of mildew or septoria prone crops, he says.

While septoria remains the dominant disease in most crops, Dr Ellerton says growers need to be on their guard against mildew.

Early 0.1 litre/ha applications of quinoxyfen (as in Fortress) are running out of steam leaving susceptible varieties vulnerable to re-infection. Spore-trapping experiments are picking up very high numbers of mildew spores, he warns.

Flag leaves are also emerging fast in E.Yorks, says Chris Straw of Acorn Agronomy. Recent wet weather means high septoria activity will be needed. Twist plus Caramba (metconazole) is his preferred mix.

"The Caramba acts as an entry to the ear sprays, starting to build up protection levels against the ear diseases and its rust control is adequate on most varieties." &#42


&#8226 Forward crops, T1 early – spray now.

&#8226 T1 late – wait for full-flag, but no later.

&#8226 T0 mildew protection running out.

&#8226 Septoria pressure still high.

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