19 May 1995

Spray those flag leaves and protect your yields

PROTECTING flag leaves from disease will be vital to protect wheat yields this season. That is despite apparently low disease levels in most areas, experts warn.

Well-timed earlier sprays and dry weather have combined to leave wheat crops looking clean. Only in Scotland have showers raised disease pressure.

But inoculum lurks in the bottom of most crops and could strike quickly if wetter weather returns, growers are warned.

"Dont forget 60% of the final grain output comes from the flag leaf," comments Keith Norman, technical director at Velcourt. "It makes sense to protect it – miss it at your peril!"

A good insurance

Velcourt trials have always shown a response to treatment, even when crops are clean, he notes. "There may not be any blemishes, but you are protecting against future disease too."

New generation triazoles like cyproconazole (Alto) and epoxiconazole (Opus) will be used as the main defence on Velcourt crops, due to longer-lasting activity and greater kickback. Fenpropimorph (Corbel) or chlorothalonil (Bravo) will be added depending on disease. "We shall tailor ingredients to variety and disease levels."

Bridget Carroll has been monitoring Septoria levels in Aubourn Farmings wheats in Lincs. "We have had very few Septoria periods. The main one was on Apr 22 and we sprayed within 12 days, so we are still covered."

But flag leaf spraying remains a priority. "Its the most yield responsive spray we do," she maintains. "And crop potential on the heavier land looks extremely good this year."

Such crops will receive 0.4litre/ha (0.28pt/acre) of Opus and 1litre/ha (0.7/acre) of Bravo to boost protection against Septoria. If delayed, triazole rate will be increased for better kickback.

On lighter land, crops are more prone to mildew, so Folicur (tebuconazole) or Silvacur (tebuconazole + triadimenol) will replace Opus. Rates will be similar unless drought pressure continues to depress yield potential. If it does rates will be cut. Tern (fenpropidin) will be added if mildew pressure is severe.

Peter Taylor, of Samco, Bishops Stortford, is advising all his clients to spray. Recommendations will vary, but will be based on a 0.5litre/ha (0.35pt/acre) rate of Opus or Silvacur with fenpropidin (Mallard, Tern, Patrol) mixed in as appropriate.

Opus tends to move more slowly in the leaf, so will be applied as soon as the leaf unfolds, he says.

"With less responsive varieties like Hussar, Hunter, and Beaufort it might be possible to split the spray 50:50 between the flag and ear, particularly if the weather stays dry," says Mr Taylor. But three weeks have passed since the last spray, so previous treatments will be running out of steam, he notes. "If we have a rain event, we wont be messing about."

Disease pressure high

In Scotland showery weather has maintained disease pressure. ELISA tests show high levels of both Septoria tritici and nodorum, says Keith Dawson of Perth-based CSC Cropcare. Mildew declined during last months cold weather, especially in crops sprayed with tebuconazole at mid-tillering and first node (GS31).

Crops look good and prices remain firm, so there is much potential to be protected, says Dr Dawson.

He has four years trials experience with Opus. "Weve found that an extra profit of £30 an acre is common," he says. "It sets new standards for Septoria control." It will be used at "targeted rates" according to sowing date, disease incidence and risk, with chlorothalonil added to boost activity and for anti-resistance. He too will use an appropriate morpholine if mildew is active. &#42