Fungicide dose-response trials in wheat: the basis for choosing 'Appropriate Dose'

Abstract

Robust, comparative dose-response data sets were produced for the most widely used fungicides applied to wheat in the UK.  This includes active ingredients from azole, morpholine, strobilurin, spiroketalamine, benzamide and carboxanilide fungicide groups.  Up to three years of data on fungicides launched in 2005 were obtained from these experiments.  These included boscalid (in mixture with epoxiconazole in Tracker), dimoxystrobin (in mixture with epoxiconazole in Swing Gold), fluoxastrobin (in mixture with prothioconazole in Fandango), metrafenone (Flexity) and prothioconazole (Proline). 

Information on these new products was published in the 'Wheat Disease Management Guide - 2005 Update'(published in February 2005) and on the HGCA web site (www.hgca.com) as an interactive tool in March 2005.

Data on strobilurin performance against S. tritici clearly show a dramatic reduction in efficacy over the period 2002 - 2004.  Despite measurements of the frequency of the resistance allele (G143A) conferring resistance to strobilurin fungicides indicating that resistance levels in the UK were generally 80-100%, there was still a measurable effect of strobilurin fungicides against S. tritici in these experiments. This phenomenon is not fully understood. 

Analysis of data since 1994 indicates a significant reduction in the activity of epoxiconazole (and by inference, all other azole fungicides) against S. tritici.  The observation of this effect in field trials was supported by laboratory-based data showing changes in the sensitivity of isolates of S. tritici.

In spite of these changes in sensitivity in populations of mildew and S. tritici, most pathogens attacking wheat crops are well-controlled by modern fungicides. The main pathogen of wheat, S. tritici, is well controlled by the azole fungicides, chlorothalonil and boscalid.  The morpholines, in mixture with azoles, also add to the control of septoria.  Although control of mildew by the strobilurin fungicides has almost been lost completely in the last few years, it is still well controlled by cyprodinil, metrafenone, the morpholines, quinoxyfen, and spiroxamine.  The azoles also still add to mildew control.  Yellow and brown rust are well controlled by many of the azole and strobilurin fungicides.    

Data from experiments were used to fit exponential curves describing the effect of fungicides on disease, green leaf area, yield and grain quality. These data typically explained a very high proportion (over 90%) of the variance.  The fitted curves and their parameters are given in the report.