Reinvestigating adjuvants for the wild oat herbicide, flamprop-M-isopropyl. II. Field performance

A field trials programme was conducted in which the performance of a new emulsifiable concentrate formulation (ECI) of flamprop-M-isopropyl containing the adjuvant. 'Dobanol' 25-7, in a ratio of 2:1 (by weight) with the AI, was compared with the current commercial formulation of 'Commando', in combination with its recommended adjuvant, 'Swirl', for the control of wild oat (Avena fatua L.) in wheat (Triticum aestivum L.) and barley (Hordeum vulgare L.). A further treatment, in which the 'Dobanol' 25-7: AI ratio was increased to 4:1 by the spray tank addition of the former, was also included. The mean results from six trials (five wheat, one barley) showed that the addition of 'Swirl' to 'Commando' was beneficial, increasing wild oat floret control from a mean value of 80% to 92% at current recommended rates (flamprop-Misopropyl, 600 g ha-1: 'Swirl', 2.5 litre ha-1). However, combinations of flamprop-M-isopropyl and 'Dobanol' 25-7 gave superior levels of control even at lower AI application rates. For example, a mean level of 96% control of Avena spp. was obtained at 300 g AI ha-1 with 1200 g ha-1 'Dobanol' 25-7 with even better control at higher rates of application of both components. This improvement in performance was accompanied by a higher risk of crop phytotoxicity than observed with the 'Commando'/'Swirl' mixtures. Symptoms initially were scorch and subsequently growth depression, particularly of tillers. None of the mean values in the six 'efficacy' trials reached commercially unacceptable levels. but in a further six 'crop effects' trials (three wheat, three barley), in which double rates were applied, the levels of phytotoxicity did become unacceptable and subsequently reduced grain yields. In contrast, two barley 'crop effects' trials gave yields higher than the control plots, possibly through the effects of reducing stem length and lodging thereby enabling more efficient harvesting. Nevertheless, there were rates of application of flamprop-M-isopropyl in the range 300-400 g ha-1 with ratios of 'Dobanol' 25-7 in the range 2:1 to 4:1 that would achieve high levels of control of Arena spp. without undue risk of crop phytotoxicity and further trials are planned to support this new adjuvant system.