19 June 1998

Strob messages are emerging but…

TRIALS to find the best way of using strobilurin-based fungicides revealed a host of messages at Cereals 98 – not all of them welcome.

Most worrying is the inability of a two-spray Landmark (kresoxim-methyl + epoxiconazole) programme to control yellow rust, says Velcourt technical director Keith Norman.

"We are disappointed to see yellow rust coming back just four weeks after flag leaf. We still cant get over the fact that the rate of Opus were putting on through Landmark seems to be having less effect than the same amount of Opus applied on its own.

"After the equivalent of two lots of 0.7 litres/ha of Opus we shouldnt be seeing yellow rust coming through, even in Brigadier." A formulation difference may to blame, he suggests.

That weakness of Landmark, plus inferior Septoria control, is not limited to Haverholme Estate. "Several of our farm managers have commented too."

A more robust treatment seems to be Amistar (azoxystrobin) plus Opus, used at GS31 and GS39. "Were not seeing anything like the same reappearance of rust here and weve got equal, if not better, Septoria control right to the bottom of the crop with equal green leaf production." Although several pounds a hectare more costly, the extra disease control would justify it, Mr Norman contends.

But for sheer strength of disease control combining half rates of Amistar and Landmark worked best. "Both strobilurin products have weaknesses, Amistars being mildew. But put the two together and you have an additive effect. Disease control is superb and there is a visibly bigger leaf canopy."

Although an expensive option this year, Mr Norman believes prices will fall. "Strobilurins should be far closer to triazoles next year. Any crop with the potential to do over 8t/ha, apart from on drought prone brash, will benefit from a strobilurin."

STROB LODGING

Do strobilurin fungicides contribute to lodging? First indications from Cereals 98 suggest they do. "My initial reaction is that Landmark is doing more to increase lodging risk than Amistar," says Mr Norman. "Were finding lodging in fertiliser overlaps now on farms where Landmark was used. We shouldnt be seeing that this early, given the robust growth regulation theyve had."

Rosie Bryson of Boxworth reckons extra green leaf retention may be to blame. "Weve found the Amistar isnt going down as much as the Landmark," she adds.

Rosie Bryson of ADAS Boxworth reckons extra green leaf retention may be to blame. "Weve found the Amistar isnt going down as much as the Landmark," she adds.