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Appropriate fungicide doses for winter barley (Volume I and II)

HGCA PROJECT REPORT 215 

Appropriate fungicide doses for winter barley (Volume I and II) 


by

S J Wale

SAC Aberdeen

January 2000

Abstract

Part 1
Evaluation of baseline physiological data for winter barley in contrasting disease situations

Summaries

A small pilot physiological study was carried out on replicated winter barley trials at two sites growing different varieties where three fungicide programmes were used to develop different disease epidemics. From GS 30 to GS 75 physiological measurements were made to assess the impact of disease on crop development. Two key findings emerged from the study. Firstly, there was a close relationship between dry matter accumulation and accumulated light interception. This indicates that the impact of disease is largely mediated through the loss of green tissue. This factor needs to be taken into account when determining the appropriate fungicide dose. Secondly, despite large differences in disease levels at the two sites, the impact on green leaf area index was similar. This suggested that the variety at one site was more sensitive to disease than the variety at the other site.

Part 2
The physiology of responses of winter barley to disease

Disease control decisions are usually made on the basis of the severity of infection and the risk of its spread. However, work on wheat and spring barley, and more recently winter barley (HGCA Winter Barley Appropriate Fungicide Doses), has shown that yield losses cannot be reliably predicted from simple assessments of disease severity. As such measurements of disease severity and forecasts of epidemic development alone are not sufficient to determine the need for fungicide applications. It is now recognised that disease control decisions should be based on an understanding of the effects of pathogens on crop function. This review examines our current knowledge of the effects of pathogens on the physiology of winter barley and considers the implications for disease control.

Part 3
Evaluation of fungicide dose and variety response curves

From data obtained in 20 field trials, fungicide dose response curves were determined for a wide range of fungicides against the four main diseases of winter barley (mildew, Rhynchosporium, brown rust and net blotch) using standard methodology. Fungicides were evaluated at five doses (0, 0.25, 0.5, 0.75, 1.0) in a replicated split plot design. One fungicide, Tilt + 0.75 Aura, was used throughout as a standard fungicide. Exponential curves of disease against fungicide dose were fitted to individual and combined data to determine curve parameters for each fungicide in protectant and curative situations for each disease. The curves presented permit relative efficacy and cost effectiveness to be determined for the first time.

In 16 trials using the standard fungicide, the interaction of disease resistance and fungicide dose was evaluated using standard methodology. For each of the four diseases, data from the trials was combined and exponential curves of disease against resistance rating were fitted for each of five fungicide doses. From the curves presented, described as variety response curves, it is possible for the first time to determine the extent to which fungicide dose can be adjusted in relation to disease resistance.

HGCA Project Number: 1397 AND 1398 
Price: £6.00 EACH

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