CROP MONITOR

Wheat Disease Manager module - Summary of performance

Summary
The Wheat Disease Manager module was used at 15 sites of the Defra 'CropMonitor' network on four wheat varieties of contrasting disease resistance. The observational data provided to WDM (i.e. expert assessments of disease severity and crop development) and the level of expertise in using the system are close to the best that could be achieved by a WDM user. Therefore, performance here provides a good indication of the maximum benefit achievable by industry from uptake of the system. The season was characterised by rapid disease development in the spring and early summer, but final disease levels were at or below the long-term averages. Response to fungicide treatment was therefore smaller than in some recent seasons which had greater disease pressure. Septoria leaf blotch was the predominant disease. Apart from its use as a source of pesticide, variety and encyclopaedic information, the value of WDM depends on supporting decisions on: (i) spray timing, (ii) product choice, (iii) dose in relation to varietal resistance, and (iv) dose in relation to site/seasonal disease pressure. The system is delivering well as follows:

Levels of septoria in the upper canopy during grain filling following treatments suggested by WDM were half those found in commercial crops. More timely sprays in the trials probably account for part, but not all, of the improvement compared to farm practice.
Product choice was appropriate to the target diseases.
On average, the total dose of fungicide input suggested by WDM was 3%, 0%, 35% and 26% lower than doses used on commercial crops of the test varieties; Consort, Claire, Malacca and Robigus, respectively. Compared to larger farms (>150hectares), WDM treatments gave reductions in fungicide input of between 7% and 44% on the four varieties and slightly improved disease control.

Post-harvest evaluation shows that the economic optimum dose of fungicide was close to zero on several sites. Across the sites, negative economic returns were obtained from about 40% of the WDM fungicide treatment regimes applied on the more resistant varieties. Since WDM generally applied less fungicide than farmers, this suggests that a greater proportion of farmers would have also had negative economic returns to fungicide treatment on those varieties this season. Cutting doses while maintaining reliable disease protection and user confidence, would require higher predictive precision than is possible with current models and weather forecast reliability.

The analyses also showed that the predictions for septoria and mildew used within WDM were inaccurate compared to the levels of disease actually observed, particularly in the case of mildew. This suggests that there is a need to improve the disease models to prevent fungicide treatments that are excessive or unnecessary, though user confidence in lower doses would again be a limitation. The general trend for over-treatment may be indicative of (i) over-estimation of disease, perhaps due to the use of weather predictions that favour disease development (ii) over-estimation of the impacts of disease (iii) under-estimation of fungicide efficacy. CropMonitor will be investigating the predictive capability of the models in more detail to evaluate their use in disease risk predictions on the CropMonitor reference crops in 2005.

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