8 March 1996

Timely advice on resistance and more…

BEWARE of using morpholine fungicides alone repeatedly in the same cereal crop – either at full or reduced rates.

Thats just one piece of topical advice in new guidelines soon to be published by the Fungicide Resistance Action Group – UK* with the backing of the Home-Grown Cereals Authority.

The aim, according to FRAG-UK chairman Dr Rosemary Bayles of the National Institute of Agricultural Botany, is help growers choose the best strategies, not only to retain the usefulness of existing products but to maintain disease control.

Fungicide resistance has been causing problems for the past 30 years, she notes. "Loss of fungicide performance because of it with the ensuing need for extra treatments to gain control can be costly to growers, agrochemical companies and the environment."

The new document, due out in April/early May, outlines the genetic basis of resistance and touches on the difficulty of interpreting field and laboratory findings. "Reduced field performance can be caused by many other factors than resistance and suspected cases need detailed examination," comments Dr Bayles.

The FRAG-UK guidelines briefly describe the background, resistance status, and field performance of fungicides on the main cereal diseases affected, focusing on powdery mildew, rhychosporium and Septoria tritici. They explore the impact of shifts in disease sensitivity and the effect of reduced doses. And they provide tactical advice and highlight areas for future research.

Also included is a table of the main fungicide groups showing how each active ingredient (with product examples) slots into a particular "family". There is also an extensive glossary to help growers understand the scientific jargon of resistance.

*FRAG-UK, combining the expertise of industry and the independent sector, was set up last year. The guidelines are based on research funded by MAFF, the HGCA and agrochemical manufacturers. Assistance also came from the Fungicides Resistance Action Committee, an inter-company technical body. &#42

Specific FRAG-UK guidelines

Powdery mildew and morpholine fungicides:

&#8226 Mixtures or "alternations" of morpholines with triazoles are generally recommended.

&#8226 Morpholines alone should not be used repeatedly in the same crop, either at full or reduced rates.

Rhychosporium and DMI and MBC fungicides:

&#8226 Many fungicide groups are active against the disease, and tank mixes or pre-formulated mixtures are control options. When a second spray is required, use a different mixture.

&#8226 An active DMI should be the lead partner mixed with another fungicide group. Three-way mixtures can be used involving DMIs, MBCs and morpholines, but may not always give better disease control.

&#8226 Other diseases present should be considered when choosing mixture partners.

&#8226 Crops should be treated in the spring at the first sign of rhynchosporium.

Septoria tritici and DMI fungicides:

&#8226 Only use fungicides in situations where the risk of Septoria tritici warrants treatment.

&#8226 Avoid repeated applications of DMIs alone to the same crop.

&#8226 Use DMIs either in combination or alternately with a suitable partner fungicide with a different mode of action. Current suitable partners include chlorothalonil (eg Bravo) and anilazine (eg Dyrene).

&#8226 Take expert advice on spray timing.