15 June 2001

Pick and choose for ear spraying success

By Andrew Swallow

WHEN and where to use an earspray on wheat will need extra careful consideration this year if maximum margins are to be made.

Pre-conceptions must be cast aside, it seems.

"Decisions have to be made at the time, in the crop," says ADAS cereal pathologist Bill Clark. "There will be crops where an earspray will not pay."

Some of those will be early sown wheats which were clean at T2 and had a robust flag-leaf spray. Other, later sown wheats which growers might be tempted to write-off after flag will benefit from the extra fungicide.

Decisions should be driven by disease pressure, which is determined by variety, T2 spray rates, disease present in the crop and weather, he says.

As a rule of thumb, if strobilurin or triazole rate at flag-leaf was less than a half dose then a T3 top-up will be needed. A T3 will also be needed if higher rates were used but, perhaps because of delayed T1 sprays, septoria is active mid-canopy.

If the crop is clean and a three-quarter rate of strobilurin and triazole was applied, then that will probably do, he says.

Velcourt technical director Keith Norman also sees opportunities to save on T3s this year.

"We are not going to see big pay backs. In the past we have used a T3 as a top-up to foliar activity, but this year disease is so low you could argue there is a case to off-set some cost."

A couple of years ago crops senesced very quickly regardless of whether they had a late strobilurin, he recalls. "It is not always the case that you get a prolonged greening effect."

Obvious candidates for a T3 are seed and milling crops, but only if it is wet within five days of flowering, he says.

That is echoed by Mr Clark. "You have to use high triazole rates – 0.5 litres/ha minimum, for fusarium. As a yield taker is not very significant, it is very visual so people tend to over-estimate the yield loss."

Apparent yield responses to fusarium-targeted controls are probably more to do with topping up the septoria and rust control from the flag leaf application, he adds.

That becomes increasingly important further north as the interval from flag leaf to harvest is stretched. "North of Notts and wheat will almost always respond to an earspray."

CSC Cropcares Keith Dawson echoes that in Scotland. "An earspray is absolutely crucial. We have had yield responses of 1.5t/ha."

At least a half dose of strobilurin plus triazole is needed, he says.

"English rates are just not sufficient for our conditions. We have a month longer to harvest and a higher infection pressure." &#42

T3 DECISIONS

&#8226 Savings opportunities.

&#8226 Consider T2 rate, variety, weather.

&#8226 Little yield loss to fusarium.

&#8226 Necessity in north.