7 March 1997

Eyespot treated far too lightly

FARMERS are simply not taking eyespot seriously enough, warns a leading pathologist.

Last years high yields camouflaged the effect of the disease, but trials carried out in 1996 showed yield losses of up to 35% and an average of 10-15%, he warns.

The trials, done by ADAS on behalf of Ciba Agriculture (now Novartis), involved 40 randomly chosen wheat fields in East Anglia. Each was sampled three times – in late March/early April, late April and milky ripe stage. Visual assessment of disease severity was made at each stage.

From the final sample, it was possible to use standard formulae to calculate potential yield losses.

"The disease seemed to come in fairly late, at GS32 onwards, when it is not normally a problem," explains Bill Clark of ADAS Cambridge.

"Higher-than-expected eyespot levels were just showing through in the latter part of the second assessment and then again in the third. These were particularly evident in Brigadier. Late infestations progressed quickly and showed high losses. Average yield losses in the trial were 10-15%.

"Most farmers do not consider eyespot a serious problem and wont look for the disease late in the season," says Mr Clark. "But they should not be complacent."

Monitoring of the disease is essential, not just at the GS31-32 stage, but right through to 2nd or 3rd node. Although it may be physically difficult to spray chemical into the base of the plant then, regular monitoring will enable farmers to consider lowering the threshold on susceptible varieties in future.

Advanced diagnostics and a new fungicide may help in time for next season, suggests Richard Leech of Novartis.

"Polymerase chain reaction – or PCR – diagnostics offer more accurate detection of eyespot than other systems and differentiate between wheat and rye strains.

"Unlike existing ELISA diagnostics kits, which work on antigen/antibody reaction, PCR works on a new genetic fingerprinting principle, making it considerably more accurate.

"DNA samples taken from infected stems are replicated up to 30bn times. A colour analysis then determines presence of eyespot lesions and split between wheat and rye types. The lab process takes about 24 hours to produce results."

Ian Chalmers, technical director of Ryehill Farmservice, has used the PCR kit in trials. "The ability to determine between W and R eyespot means we can now target the disease using the right molecule, at the right time and for the right reason. The system removes potential for error in management decision making."

Mr Leech hopes to have the kit available in its present form by next season. "We are continuing to develop the system further, with the ultimate aim of determining disease intensity levels," he adds.

Mr Clark believes the launch of Novartiss new eyespot fungicide, cyprodinil, next season could provide the industry with its best eyespot control yet.

"Cyprodinil is the best eyespot fungicide we have ever seen. In ADAS trials it is the only material to achieve 100% control, albeit in barley. The closest other chemicals achieved was only 60%," he highlights.

"From what we have seen of cyprodinil in trials, we can expect 50-80% disease control," Mr Leech adds. "Eyespot is a yield robbing disease, so by treating the disease appropriately, a benefit may be seen.

"Where eyespot has proven to be present, French farmers using cyprodinil have typically seen a 0.4t/ha yield benefit."

Complacency over eyespot control could cost growers more than they imagine, according to ADAS. New technology may come to their aid.


&#8226 ADAS-Ciba survey.

&#8226 Average yield loss 10-15%.

&#8226 45% of crops suffered losses of 5-20%.

&#8226 Yield losses up to 35%.


&#8226 Infected stems taken from field.

&#8226 DNA samples taken from diseased material.

&#8226 Replicated 30bn times for accuracy.

&#8226 Colorimetric analysis shows infection presence.

&#8226 Wheat and rye type determination possible.