18 February 2000

No blueprint for strobs

Making the most of business

and crop management

advice was the theme of a

conference organised by

distributor ProCam in

Newmarket, Suffolk last

week. Andrew Swallow

reports the highlights

THERE is no set formula for making the best of strobilurin fungicides in cereals and there will be crops where conventional chemistry remains more economic, an agronomy meeting in Newmarket heard last week.

"The person that gives you a blueprint to use is wrong," ProCam technical director, David Ellerton, warned delegates. "You need to tailor rates, products and timings."

Where growers had done that with strobilurins last season yields were 23% higher than crops treated with non-strobilurin programmes, according to monitoring data from the firms Crop Management System.

For crops where most of the yield will come from photosynthesis in the ear and top two leaves and where water is not limiting, strobilurins are best saved for T2 and T3 timings, he said. That means wheats on heavy soils, early sown and thick crops, and also crops in the north.

T1 strobilurins may also be wasted on take-all prone second wheats. If the disease fails to develop strobilurins can be deployed later. But early applications are redundant if the disease becomes dominant, he said.

In thinner crops, including late sowings, more yield is contributed by leaves three and four. That makes a strobilurin at T1 or GS32 more important to preserve them. Rapid senescence in the south and on light soils also makes a T1 and T2 approach a better bet.

For wheats aimed at milling markets a T3 strobilurin is worthwhile to boost grain quality, especially specific weight. On lighter soils that may mean using conventional chemistry at flag leaf to come back with the strobilurin as an ear spray, he noted.

Crops with very high yield potential warranted three strobilurins, despite the FRAC anti-resistance guidelines, Dr Ellerton suggested.

However such crops have to be exceptional for three strobilurins to get the best economic response. In most wheats a two-spray sequence is most consistent.

"Growers have to think very hard before using three strobilurins. But the most important part of the FRAC guidelines on strobilurin use is to mix and get sprays on early in the life cycle of the disease."

For some wheats non-strobilurin programmes will still give the best return. Disease resistant varieties, drought susceptible sites and take-all prone crops should all make growers question the expense of strobilurins. "And there seems to be less of a response in the south-west. Conventional programmes are not dead," Dr Ellerton said.

No matter what the programme, lower rates of strobilurin produce the best returns economically. In general, the more resistant the variety, the lower the dose of strobilurin that is appropriate, he said.

"If you spend more you can increase the yield. But across all varieties it is the half or quarter dose that works out most cost effective." But growers should aim for a minimum of one full dose over the season and use a minimum half-rate at any one timing, he added.

TARGET T1 STROBS

&#8226 Thin wheats, early or late drilled.

&#8226 Light soils, especially in south.

&#8226 Wait and see with take all.

&#8226 Use at T2 + T3 on heavy soil.

Strobs for all barley

In 1999 NIAB trials strobilurin programmes on barley averaged 8% more yield than conventional chemistry, compared with only a 3.5% edge in wheats, noted Dr Ellerton. All winter barley crops are likely to merit a strobilurin at T1 and a T1 plus T2 sequence gives the most consistent response. "You need to go early with the strobilurin and if eyespot is present add Unix." The T2 decision should be based on the disease pressure at the time, especially net blotch, brown rust and ramularia, he continued. "Azoxystrobin is streets ahead on net blotch and brown rust, but trifloxystrobin looks to have the edge on rhynchosporium."

&#8226 PSD meet on Feb 24 to discuss the approval of the Novartis strobilurin, trifloxystrobin.

Save strobs until later for thick crops on heavy soils, suggested ProCams David Ellerton at last weeks agronomy meeting. The early money would be better spent on more curative conventional chemistry.