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eyespot

27 November 1998

Strong strategy for

eyespot

WHEAT growers best strategy for combating eyespot is a routine application at early stem extension of a broad-spectrum spray with activity against the disease.

That approach makes sense because accurate visual diagnosis of the disease is virtually impossible in its early stage, which is when treatment is most effective, says AgrEvos Eileen Bardsley.

According to the companys countrywide wheat stem base disease surveys in 1997 and this year R-type eyespot is by far the most prevalent. The accurate PCR test used showed its incidence ranged from 64% of the crops sampled in southern England to 80% of the crops in the north-west.

Of almost 40% of samples taken from wheat following broad-leaved crops, 62% were infected with R-type eyespot. Probably a two-year break is needed to achieve a significant reduction, suggests Ms Bardsley.

The surveys also shows drilling date does not begin to have a significant effect until late October. Even then over 50% of crops drilled from then on were infected.

"Deep ploughing is useful for reducing eyespot, because the soil it brings up will carry less infective material," she notes. "But minimal cultivations keep that material on or near the surface and spread it around more."

eyespot

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Eyespot

31 March 1995

control advice

Eyespot

By Robert Harris

EYESPOT lesions can be readily found in many wheat crops across the country. Serious cases need controlling now, but others should be monitored and treatment delayed if possible to allow timely septoria control as well, advises one expert.

Levels of eyespot are higher than for several years due to the mild, wet autumn and winter, says David Jones, plant pathologist at ADAS Rosemaund. Early-drilled and second and subsequent wheats are showing most symptoms.

Crops should be monitored for disease from now on, he advises. Where more than 20% of tillers are infected with penetrating lesions – those that have penetrated through the outer leaf sheath through to the next one – a spray should be applied now.

Fungicide choice depends on the need to control additional foliar disease, says Dr Jones. Prochloraz (Sportak 45) is likely to be the most effective treatment against severe eyespot, but it will need tank-mixing with another fungicide (or a co-formulation used) where there is a risk of mildew or yellow rust, he advises.

Flusilazole (eg Punch C, Sanction) could be used where there is less risk of severe eyespot. This has a broader spectrum of activity against foliar disease, he adds.

If lesions have not penetrated, treatment should be delayed as close to GS32 as possible to allow effective septoria control at the same time, he suggests.

Return visit

Going now means a return visit will probably be needed to control that disease. "Its a long time to flag leaf emergence. The chances are you will have to go back at the end of April or early May."

Patrick Vernié of AgrEvo believes growers with high risk crops should consider applying Sportak even where thresholds have not been breached. "The disease will have started to develop, but will only show after the optimal time for treatment has passed. I would still spray at GS31-32."

He suggests a 1l/ha (0.7pt/acre) rate of Sportak Delta as insurance. "The prochloraz element gives very good kickback on septoria, and cyproconazole is excellent on rust."

Where eyespot is above threshold levels, he recommends a higher 1.25l/ha (0.9pt/acre) rate, or 0.9l/ha (0.65pt/acre) of Sportak 45.

Mike Thomas of Du Pont reckons more first wheats than normal are infected with eyespot, but overall levels are lower than once feared. "There is a fair amount about, but it is not as intensive as we might have thought."

Moderate to high eyespot levels should be treated with a 0.5l/ha (0.35pt/acre) rate of Sanction (flusilazole); lower levels with the standard 0.4l/ha (0.28pt/acre), he suggests. "Trials show levels of eyespot control are very similar to prochloraz," he claims.

He advises growers with septoria not to delay too long. "Weve picked up a dramatic increase in Septoria nodorum this year with our diagnostic kits. It is much more aggressive than tritici, and harder to control curatively." Local Du Pont distributors can advise on the likelihood of nodorum in the area, he adds.

Eyespot – less severe than thought, so it may pay to delay treatment until GS32 when foliar diseases can be targeted too.

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