Effect of adjuvants on the performance of the new cereal fungicide, metconazole. I. Glasshouse trials

Metconazole, (1RS, 5RS; 1RS, 5SR)-5-(4-chlorobenzyl)-2,2-dimethyl-1(1H-1,2,4-triazol-1 -ylmethyl)cyclopentanol, is a highly active fungicide, in particular controlling seed-borne and foliar diseases of cereals, such as wheat (Triticum aestivum L.) and barley (Hordeum vulgare L.). In order to maximize its foliar activity, an experimental survey of some types of surfactants and an emulsifiable oil was undertaken. Two types of metconazole formulation were investigated using a biological assay involving the therapeutic control of two diseases (Erysiphe graminis DC f. sp. tritici Marchal and Leptosphaeria nodorum Muell.) of wheat. Enhancements of activity by 'Genapol' C12/C14 alcohol ethoxylates of an emulsifiable concentrate (ECM) formulation of metconazole were approximately three- to four-fold. For its, initially, less active suspension concentrate (SCM) formulation, enhancements were around 35-fold, so that with these adjuvants the two formulations were of similar activity. The enhancement ability of these 'Genapol' surfactants was optimal at lower (5-10 moles) ethylene oxide content. These analogues induced marginally better enhancements of activity than members of a range of nonylphenol ethoxylates ('Arkopal'), and emulsifiable paraffinic/naphthenic oil (HVI 60E) and a castor oil ethoxylate ('Atlas' G1281) but were equivalent to a similar series of alcohol ethoxylates ('Dobanol') from another source. Varying the alkyl chain length between C9-C11 and C14-C15 in the 'Dobanol' series had little effect on their high enhancements of metconazole activity. It was determined from trials varying the application rate of the best alcohol ethoxylates that application rates of 1-1.5 kg ha-1 were required for maximum activity. This implied the use of high adjuvant/metconazole ratios in one-pack adjuvant-containing formulations. A range of soluble liquid (SL) formulations were prepared with either 'Dobanol' 23-6.5 or 'Dobanol' 91-6/metconazole ratios varying from 5:1 to 15:1. There were found to be highly active and were recommended for field testing.