Sensitivity of barley powdery mildew to morpholine fungicides

Summary

Sector:
Cereals & Oilseeds
Project code:
PR127
Date:
01 August 1989 - 30 July 1992
Funders:
AHDB Cereals & Oilseeds.
AHDB sector cost:
£60,578 From HGCA (Project No. 0009/01/88B)
Project leader:
Part I. S Robertson, J Gilmour, D Newman and J H Lennard, SAC-Edinburgh Part II. D W Hollomon, IACR-Long Ashton

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About this project

Summary

Part I: Work in Scotland

This study took place at a time when barley growers were heavily dependent on fungicides for the effective control of powdery mildew and when the morpholines had been the most widely used for several years in Scotland.

A considerable range of variation of sensitivity was found to all three of the fungicides tested; Calixin (tridemorph), Mistral (fenpropimorph) and Patrol (fenpropidin). Variation of sensitivity to Calixin was least (4-fold) and most consistent over years. Variation of sensitivity to Mistral and Patrol was much greater (up to 17-fold and 44-fold respectively) and the range more variable from year to year.

Mean annual sensitivities to the fungicides changed from year to year, but although sometimes statistically significant these changes were small. Sensitivity to Calixin declined over the four year period. Sensitivity to both Mistral and Patrol increased from 1988 to 1989. Sensitivity to Mistral showed little change thereafter, while sensitivity to Patrol returned to the 1988 level.

Very few isolates showed reduced sensitivity to two fungicides, but a small number of isolates contained components that could grow in the presence of the highest concentrations of Mistral and Patrol used in these tests. This may indicate an adaptive capability of some of the populations of barley powdery mildew in Scotland.

Very limited work with one fungicide mixture, Dorin (triadimenol and tridemorph), suggested that such mixtures may be very much more effective than the component fungicides used alone.

There was no apparent correlation between sensitivity and fungicide used in the field before the isolates were collected.

Part II: Work in England and Wales

1. Differences in sensitivity to morpholine fungicides can be detected by different assay methods although the assays may reflect different aspects of morpholine action.

2. The range of variation in sensitivity encountered in both barley and wheat powdery mildew is large, but all isolates were controlled by recommended rates of fungicide. There was no evidence of resistance causing performance difficulties in field crops.

3. Barley mildew populations in England and Wales were possibly more sensitive to morpholine fungicides than those in Northern Scotland.

4. Sensitivity to morpholine fungicides can vary from year to year, but changes were unrelated to fungicide use.

5. Several novel fungicides with new modes of action are becoming available in the UK. These should be used as alternatives to morpholines in mixtures with DMI fungicides.

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