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Understanding the effects of new fungicide on disease development, crop growth and yield

HGCA PROJECT REPORT 261 

Understanding the effects of new fungicide on disease development, crop growth and yield 

by

D R Jones
ADAS Rosemaund, Preston Wynne, Hereford, HR1 3PG

V Shearman
Division of Agriculture and Horticulture, School of Biosciences,
University of Nottingham, Sutton Bonington Campus,
Loughborough, LE12 5RD

&

R Sylvester-Bradley
ADAS Boxworth, Boxworth, Cambridge, CB3 8NN

SEPTEMBER 2001

Abstract

Field experiments were undertaken for three years at two sites to investigate whether strobilurin fungicides have physiological effects on winter wheat that could be detected and exploited in the field, and to test the effects of mixing strobilurins with azole fungicides.

On a resistant cultivar at a low disease site, there were consistent yield increases resulting from strobilurin application, although yield responses were smaller than at the site with severe disease. Dose-response curves for strobilurins were mostly similar to those for azole fungicides but, in one instance, azoxystrobin showed a steeper curve with low curvature, indicating that there would have been increases in yield at doses above the maximum tested (the full commercial rate of 1.0 litre/ha). Experiments on the interaction between fungicides and nitrogen assimilation indicated that strobilurin fungicides did not affect nitrogen uptake, but there was an indication (not statistically significant) that the optimum nitrogen rate was slightly higher for azoxystrobin and kresoxim-methyl, compared with epoxiconazole or an untreated control. There were no differences between strobilurins and epoxiconazole in maximum green area index, and no evidence of any effect of strobilurins on radiation use efficiency either pre-anthesis or post-anthesis.

Under conditions of severe foliar disease, mixtures of a strobilurin (azoxystrobin or kresoxim-methyl) with epoxiconazole gave greater persistence of disease control than epoxiconazole alone, resulting in greater green canopy duration. Canopy size showed a close inverse relationship with disease, and yield was closely correlated with canopy size. In an experiment on interaction with seed rate, there were effects of fungicides on disease, and of both fungicides and seed rate on canopy size, crop biomass, grain yield and harvest index. However, there were no statistically significant interactions between fungicide and seed rate.

There were no clear indications that yield increases resulted from physiological effects on the crop. However, it is possible that conventional assessments of canopy and crop growth are not sufficiently sensitive to detect small differences that may result from physiological effects. The possibility that strobilurins do affect crop physiology cannot be discounted but, since any such effect is likely to be small, it would need extensive and sensitive experimentation to identify and characterise it. Under conditions of severe disease, yield was strongly correlated with increase in canopy duration, and there was no evidence of any physiological effects of strobilurins. Overall, these results show that the value of physiological effects to growers under normal conditions of moderate or high disease risk would be small in relation to the large fungicidal effects that occur consistently.

It can be concluded that strobilurins are a valuable addition to the fungicide armoury available to growers, providing long-lasting protectant activity to complement the eradicant activity of azole fungicides. Mixtures were generally efficacious for disease control. There were no antagonistic effects between azoxystrobin and epoxiconazole, and indications that mixtures showed synergism. If there are additional physiological effects of strobilurins on wheat, they should be regarded as an added bonus from use of these fungicides, rather than a core feature of their activity. The experiments on interaction of strobilurin with seed rate, cultivar and nitrogen showed that there is no need to alter the basic agronomy of the crop in order to gain maximum benefit from strobilurins, except for a small increase in nitrogen rates to exploit the greater yield potential.

HGCA Project Number: 1306 
Price: £7.50

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