13 November 1998

Eyespot survey provides disease control pointers

By Charles Abel

NEW data from a national survey of eyespot could help growers combat the disease more effectively next season.

Almost 230 samples collected from winter wheat fields around the UK were checked for eyespot incidence and severity using PCR diagnostic testing.

The results provide new pointers to guide disease control decisions, says Steve West, cereal fungicides development manager for Novartis in Europe.

"We know from survey work in 1996 and 1997 that spraying according to traditional risk criteria and symptoms seen at T1 can miss crops. In 1996 80% of crops lost over 5% yield due to eyespot, yet just 40% were treated," he says.

Key finding from the study is that R-type eyespot is more widespread than first thought. That does not reflect greater sensitivity of the diagnostic test, Mr West says.

"There have been concerns about the sensitivity of other tests, but we are confident from the cross checking we have done that what we detect is what is there."

The study confirms the belief that early drilling on heavy/medium soils causes most risk. But it also shows R-type eyespot can be a concern on lighter soils, affecting 60% of surveyed crops on such fields.

R-type also appears more prevalent in early drillings, accounting for over 80% of infections, compared with 30% for W type.

Scotland also seems significantly more at risk than thought. Over 90% of samples were infected with R-type eyespot.

Prior cropping had little effect. "Breaks do not seem to reduce eyespot risk, which confirms other work showing at least two years are needed to reduce risk."

Unlike other fungicides, Unix (cyprodinil) is equally effective against W and R strains, Mr West says. &#42

EYESPOT CONTROL

&#8226 230 samples tested.

&#8226 PCR diagnostic check.

&#8226 More R-type than thought.

&#8226 Consider when planning control.