2 March 2001

Stick to guides to maintain its effectiveness

OVERUSE of strobilurins is a serious concern, says Nigel Hardwick, chairman of the independent Fungicide Resistance Action Group-UK.

The latest Pesticide Usage survey found advice aimed at preserving their effectiveness was frequently ignored in 2000.

Contrary to FRAG guidelines that individual crops be sprayed with strobs no more than twice, 36% of the winter wheat area was treated with them three times, and 4% four times.

The danger is that unless growers change their ways and follow resistance management guidelines there is a high risk that the products will no longer give adequate disease control, warns Dr Hardwick.

Experience in several countries, including recent MAFF-funded UK research, emphasises the need to limit the number of strobilurin sprays if resistance is to be managed successfully.

Serious problems have already built up in parts of northern Europe where wheat mildew has become strob-resistant.

Resistant mildew

Resistant strains of wheat mildew have already been found in this country. "In the UK practical resistance problems are likely to occur soon."

Fortunately no signs of strob resistance in the key cereal diseases, namely septoria in wheat and rhynchosporium and net blotch in barley, have yet been detected. But the mildew experience should serve as a warning, stresses Dr Hardwick.

Although strobilurins clearly offer benefits, disease control is their main function. "It should not be jeopardised by excessive use," he says. &#42

FRAG-UK ADVICE

&#8226 Apply strobs only twice on any one cereal crop.

&#8226 Use manufacturers recommended doses and intervals.

&#8226 Where appropriate use in mixtures with fungicides with different modes of action such as:

DMIs (eg Alto, Folicur, Opus)

Cyprodinil (eg Unix)

Chlorothalonil (eg Bravo)

Morpholines (eg Corbel, Patrol)

Quinoxyfen (eg Fortress)

MBC (eg Bavistin).