The use of fungicide sequences to maximise the control of eyespot in cereals and minimise the risk of sharp eyespot.

Summary

Sector:
Cereals & Oilseeds
Project code:
PR200
Date:
01 February 1998 - 31 December 1998
Funders:
AHDB Cereals & Oilseeds.
AHDB sector cost:
£15,633 From HGCA (Project No. 1088)
Project leader:
F J Burnett

Downloads

pr200-material-method-result pr200-discussion-and-conclusion pr200-introduction

About this project

Abstract

This project report describes the results of a one year field trial carried out to investigate the control of common eyespot and sharp eyespot. Controlling one disease may allow another disease to colonise the clean stem base and one aim of this project was to investigate if controlling common eyespot would lead to an increase in sharp eyespot and if this could be suppressed.


Previous work on common eyespot has shown that the two most effective fungicides with activity against common eyespot have different optimum timings of application. Prochloraz works best when applied during the period of mid tillering to the start of stem extension. Cyprodinil works best when applied later at the second node stage of stem extension. Both fungicides cause an initial suppression of the eyespot population, but levels of eyespot then increase again. Successful treatment depends on getting a large enough initial reduction in the population coupled with a more sustained period of reduction before the eyespot population recovers. This project aimed to establish if using the two fungicides in sequence at their optimum timings would allow for a longer period of reduction and hence a more successful eyespot treatment.


The project found the most effective treatment for common eyespot control of those evaluated in the trial was cyprodinil applied at GS 32 as a single full dose treatment. Splitting this dose of cyprodinil between GS 30 and GS 32 was not as effective as the single full rate application. Prochloraz applied at full dose rate at GS 25 also reduced the levels of eyespot assessed at the end of the season. Splitting the prochloraz treatment between GS 25 and GS 31 did not improve eyespot control.


Splitting the eyespot treatment and applying half dose rate prochloraz at GS 25 and half dose rate cyprodinil at GS 32, so that each was applied at it's optimum timing, was not as successful at reducing visual eyespot as cyprodinil either as a single full dose application at GS 32 or as a split treatment as GS 30 and GS 32. PCR analysis, however, shows lower levels of eyespot DNA in the prochloraz followed by cyprodinil treatment than in these other treatments, which may support the theory that better eyespot control could be achieved by using both products at their optimum timing than could be achieved using either one straight. The yield from this split treatment of prochloraz and cyprodinil was also higher than cyprodinil applied on its own.


Analysis of the eyespot DNA present showed that the R strain was the dominant strain at the site and that the W strain of eyespot was only present at very low levels. In this trial eyespot was not seen until the crop was heading with no eyespot present at the critical time for making an eyespot spray choice, of stem extension. This shows how a threshold approach to treating this crop would not have been successful, and also demonstrates how the fungicides worked well as protectants in reducing final eyespot levels in the plots.


Sharp eyespot levels in the trial were very low, but there was a small increase in sharp eyespot levels following the most successful eyespot treatments and there was a negative correlation between sharp eyespot and common eyespot at the end of the season. A sequence of azoxystrobin sprays were applied and, of the timings evaluated, the spray applied at GS 32 was the most successful at reducing sharp eyespot as well as increasing yield and reducing lodging.

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