Appropriate fungicide doses on winter wheat: research information for growers on the control of powdery mildew, brown rust and septoria nodorum

Abstract

Growers bear the costs of protecting wheat against the effects of foliar pathogens. Despite an annual spend of approximately £100 million on fungicides for winter wheat, national survey data show annual losses to disease that fluctuate, according to disease pressure, around £40 million. There is still much that can be done to improve the efficiency of disease management, to the benefit of the unit cost of production.

Efficiency improvements depend on the ability to select the most cost-effective fungicide/s for the combination of pathogens which pose a threat to a particular crop, and apply a dose that is appropriate to the degree of disease risk. Product selection requires knowledge of comparative fungicide performance. Choice of dose depends on knowledge of the relationship between disease risk and the dose at which net economic output is maximised - by definition, the 'appropriate dose'.

The HGCA project 'Appropriate Fungicide Doses for Winter Wheat' began in 1994 and introduced the concept of appropriate fungicide doses. The first three harvest years focused on the control of Septoria tritici and yellow rust. This report covers appropriate dose experiments carried out since 1996.

Comparative dose-response curves are presented, summarising the performance of the major fungicide active ingredients against powdery mildew, brown rust and Stagonospora (previously Septoria) nodorum glume blotch. The products tested included a range of novel active ingredients, including strobilurins.

To be of enduring value to the industry, information on the performance of products needs to be kept current. In particular, novel fungicides will continue to enter the market and their performance relative to products in the existing data set will need to be assessed. It would be inefficient to re-run multi-site experiments with the entire range of existing fungicide active ingredients, each time a new fungicide appears, in order to allow a direct comparison. A statistical method has been developed, tested and reported here, which allows new fungicides to be assessed in relation to a small number of 'standards', which can then be used to relate performance of that product to others in the extant data set.

Resistance genes incorporated in wheat varieties by conventional breeding techniques marker assisted breeding or plant transformation are likely to be increase in their importance over the coming decade. Exploiting the potential benefits of these improvements depends on being able to assess the extent to which increases in resistance decrease the appropriate dose. Data are presented on the impact of varietal resistance on fungicide dose-response curves, as a step towards that goal.

The results presented in this report will be summarised and set into a practical crop management context in the HGCA Wheat Disease Management Guide, due for publication in 2000.