Validation of a risk assessment method to identify wheat crops at risk from eyespo

Abstract

Eyespot (causal organisms Oculimacula yallundae (W type) and / or O. acuformis (R type)) is a damaging disease of the stem base in winter wheat crops.

Replicated field trials in 2004, throughout the UK, showed that the new triazole, prothioconazole, tended to improve eyespot control and yield when compared to the standard treatment of cyprodinil plus epoxiconazole.

A second new fungicide, metrafenone, was tested at one site and also showed improved eyespot control and yield when used at the full rate. Both controlled both R and W type eyespot, in contrast to prochloraz which controlled only W type. R and W type eyespot were present at all sites as mixed populations in samples taken at stem extension, with W type being the dominant species. The proportion of W type eyespot increased when the same sites were tested at the end of the season.

A risk assessment model, produced in HGCA project 2382 and reported in Part 1 of Project Report No.347, was used to assess the need for eyespot treatment at each trial site. The model correctly predicted the need to treat or not treat (based on >30% incidence of eyespot by the end of the season) for 69% of the test sites. It was correct 54% of the time when predicting an eyespot incidence greater than 45%. The results show that the model approach to judging treatment need has potential and that it was better than the former 20% threshold approach to judging treatment need. The 20% threshold had a high number of false positives in its judgements, which could lead to pesticide usage being increased.

More work is needed to refine and progress the model and incorporate more information on weather factors.