7 March 1997

Strobilurins promise that little bit extra…

Novel fungicides, growing disease risks and new ways to prevent them are examined in this special fungicide focus. Robert Harris opens with a look at the new strobilurin compounds which promise more than mere disease control. Edited by Andrew Blake

FUNGICIDES or fertilisers? While they will be marketed very much as the former, the new strobilurins give much higher yield responses than can be explained by disease control alone, says Bill Clark, ADAS national plant pathologist.

Two molecules, kresoxim-methyl from BASF, and azoxystrobin from Zeneca, could be available this year, he says. Zeneca has another in the pipeline, likely to be sold before the other 20-plus companies involved with strobilurins market theirs.

A striking feature of the new chemistry is its effect on output. "We could be talking about a 10% yield enhancement over and above the disease control effect," he says.

So far, little work has been done to discover why. Mr Clark believes there are several reasons.

Strobilurins are powerful protectants which may help avoid subclinical disease damage. "Septoria grows in the leaf for three to four weeks before it shows as visual symptoms. That could be debilitating, inflicting a metabolic penalty on the plant. With strobilurins, fungus never gets inside the leaf – it is killed on arrival."

Strobilurins also keep plants greener. "Crop greening is one thing farmers will notice. It is quite dramatic, especially on the lower leaves."

The value of that is debatable, he admits. "Lower leaves do not contribute much to yield." But more chlorophyll distributed throughout the whole plant could boost carbohydrate levels.

In theory, greener crops could suffer on droughty sites, due to higher water demand later in the season. That could affect grain fill. "We have not seen a negative effect yet, but it is possible."

Strobilurins are kinder to crops than existing fungicides, he adds. "Many conventional fungicides have a direct growth regulatory effect. Strobilurins are very benign, so that could give a slight yield effect as well."

To obtain full yield boost, strobilurins need to be used at or near full rates, stresses Mr Clark. "Farmers will have to take a lot of what is said with trust. There is no way of judging performance in conventional terms. They will not notice any difference in disease control if they use a half rate – it will probably be as good as any they have ever seen. But they wont necessarily get the same yield benefit."

Strobilurins lift wheat yields by more than expected from disease control alone, says ADASs Bill Clark (inset).


STROBILURIN PLUSSES


&#8226 Most are protectant.

&#8226 Little subclinical disease penalty.

&#8226 Greening effect on crop.

&#8226 Long persistence.

&#8226 Kind to crop.