8 August 1997

Over-green cereals

prompt concerns over harvest date

EXTRA-GREEN cereal crops treated with strobilurin fungicides are causing concern at some ADAS trial sites.

"Crops are so green it looks like harvest is going to be put back 10-12 days," says Bill Clark, ADAS national cereal pathologist based at Boxworth. "Farm managers are banging on my door asking when crops are going to be ready to cut."

Plots on silts at ADAS Terrington are particularly affected, due to high mineral N and soil moisture levels, he notes. The effects are also noticeable to a lesser extent on the heavy clays at Boxworth.

At Terrington, plots received 1 litre/ha of a mix of kresoxim-methyl (as in Ensign) and epoxiconazole (Opus), or azoxystrobin (Amistar), in two or three splits between second node detectable (GS32) and flag leaf emerged (GS39).

"Those are not huge amounts. But strobilurins are so persistent they are preventing secondary moulds from establishing on leaves. In conventionally treated plots those have helped crops senesce. We still have three green leaves in some cases at the end of July."

Grain nitrogens may also suffer, partly because of the dilution effect of expected higher yields, and also because nitrogen is being retained in chlorophyll-binding proteins.

"In previous years, crops stayed green, then senesced simultaneously rather than from the bottom up. It doesnt look like that is going to happen this year."

John Bedford, marketing manager for BASF, disagrees. "Evidence shows that harvest will not be delayed beyond the time you would expect a disease-free crop to ripen." High disease levels this year have caused some crops to senesce quickly, exaggerating the difference, he adds.

Steve Yates, Zenecas fungicide product manager, maintains several years of trials show no delay in harvest date. "Azoxystrobin keeps the crop greener for longer, but then it senesces very rapidly," he notes.

Eastern barometer grower Philip Godfrey reckons crops treated with straight strobilurins at full and reduced rates are senescing as fast as others. Trial plots treated with kresoxim-methyl and epoxiconazole are slightly greener on stems and flag leaf. "But I cant see it will make much difference to harvest date."

&#8226 The two strobilurins appear to have different effects on crop lodging, says Mr Clark. Plots treated with azoxystrobin are slightly taller, but plants are standing bolt upright even under high nitrogen regimes. Others, including those treated with kresoxim-methyl, have gone flat, he notes.

"Azoxystrobin could be promoting a bigger root plate, making the crop less prone to lodging."

Mr Yates has received reports of better lodging resistance this season. "Azoxystrobin may be promoting healthier stem bases. But I am not aware of any work to assess its effect on rooting."

Mr Bedford admits there is evidence of lodging with kresoxim-methyl treated plants. Those crops which received a sensible growth regulator regime are OK."n

STROBILURIN GREENING

&#8226 10-12 day harvest delay?

&#8226 Foliar mould control blamed.

&#8226 N content may also suffer.

&#8226 BASF and Zeneca say not.

&#8226 Also lodging implications.