1 March 2002

Circumstances ideal for bad eyespot year

ALMOST every wheat crop has some level of eyespot in it this year, warns Chris Rowsell technical manager with Syngenta.

"Everything growers did last autumn went in the diseases favour," he says. "More wheat went into the ground, much of it was early drilled and there was greater use of minimum cultivations.

"Added to that, there havent been any varietal improvements in resistance. So the risk has been increased considerably."

Weather also played a part. "It was very mild. Crops drilled early had an extra months growing season. That gave the disease more time to invade the plant."

Eyespot is normally associated with second wheats, says Mr Rowsell. "But this year, first wheats are at risk. Its a trash-borne disease, so whether ploughing or min-till was used, crops were drilled on top of inoculum."

Identifying eyespot in the early stages is not easy, he admits. "PCR diagnostics is the best method. The disease starts as a dirty brown smudge and develops into an oval, eye-shaped lesion with a defined margin."

The R-type strain now dominates, with 70% of samples showing this strain and only 4% having the W-type alone. But triazole fungicides are less good at controlling R-type eyespot, he notes.

"Remember that you can lose 35% of yield with eyespot. So use the most appropriate product – Unix (cyprodinil) will control both strains."

Spraying can achieve good results up to the third node detectable stage (GS33), but growers should aim for GS31/32, Mr Rowsell advises. "The eyespot product can be added to an existing tank-mix then."

Deciding whether to treat depends on considering all the risk factors, he suggests. "Look at drilling date, the weather conditions, symptoms showing in the crop, its place in the rotation and establishment method.

"But most importantly, go and look for the disease," he stresses. "Growers are often only concerned with foliar diseases. This year, they must be aware of eyespot."

&#8226 Most wheats infected this spring.

&#8226 Many factors in diseases favour.

&#8226 First wheats unusually at risk.

&#8226 Careful field assessments advised.

Growers using Unix at T1 for eyespot control can expect good control of Septoria nodorum too, reports ADASs David Lockley.

Trials last year in Cornwall showed a significant effect on levels of glume blotch when cyprodinil was included in the T1 tank-mix, he notes.

"Septoria nodorum is often overlooked, but it is an important disease in the south-west. It is difficult to spot, as you cant see the picnidia, but it develops quickly and can take out the flag leaf in just two weeks."

Opus (epoxiconazole) and Amistar (azoxystrobin) are also effective against S nodorum. "But neither works on eyespot. So in a situation where both diseases threaten, Unix has a role."

More crops than usual could need treating against eyespot this season.