Physiological effects of strobilurins and plant activators in relation to yield of winter wheat

Abstract

Three experiments were undertaken in a one-year pilot study in 1997 to investigate whether new fungicides, particularly strobilurins, had effects on growth and yield of winter wheat additional to those associated with disease control. The strobilurin fungicides azoxystrobin (as Amistar) and kresoxim-methyl (co-formulated with epoxiconazole as BAS494) were evaluated in two spray programmes at GS 32 and GS 39, in comparison with the azole fungicide epoxiconazole (as Opus). Additional programmes of Amistar and Landmark were designed to exploit the perceived strengths of each product. In addition, there was a treatment with the plant activator benzothiadiazole (as A9180) at GS 30, followed by Opus at GS 39.

Severe Septoria tritici on cv. Consort was controlled well by Opus and BAS494, but Amistar was less effective and suffered earlier loss of canopy due to disease. All these fungicides also gave good control of yellow rust on cv. Brigadier. There was no evidence that benzothiadiazole could substitute for a conventional fungicide at GS 32 where either of these diseases was severe. Compared with Opus alone, the mixture with kresoxim-methyl gave small additional increases in green canopy duration, although disease control was no better. On the resistant cv. Pastiche, disease incidence was negligible, but fungicides delayed leaf senescence. BAS494 treatment resulted in increased chlorophyll content of the lower leaves compared with Opus, and showed decreased light transmission through the leaves, which suggests that photosynthetic rates could have been higher, although this was not determined.

Control of S. tritici resulted in yield increases of up to 6.06 t/ha. Yields from BAS494 were significantly higher than those from Amistar, with Opus intermediate. There were no differences between fungicides in yield response to yellow rust control, with increases in the range 2.04-2.58 t/ha. On cv. Pastiche, disease levels were very low, but all fungicide treatments delayed canopy loss and increased yield by up to 1.03 t/ha. The largest increases were from BAS494, followed by Amistar.

This pilot study showed that strobilurins, particularly kresoxim-methyl, increased green canopy persistence and chlorophyll content. Further investigation is required to determine the magnitude and consistency of these effects, and to show whether photosynthetic activity is increased. There were also small yield benefits over azole fungicides. The lack of eradicant activity of azoxystrobin against S. tritici on a susceptible cultivar was demonstrated and, where there is a high risk of disease, this fungicide will need to be mixed with an azole fungicide if other benefits are to be expressed.