CROP MONITOR

Growers Advised to Scrutinise T1 Application Timing

Press release by Bayer CropScience, 9 March 2006

Results from the last three years of the CropMonitor service suggest that many T1 sprays are being made up to ten days too early.

CSL principal plant pathologist Dr Judith Turner points out that although final leaf 3 emergence is the target at T1, the reality is that many crops are being sprayed before this at final leaf 4 or 5.

"The average date for the T1 spray is April 23," she reports. "That means it is often applied to leaf 4 instead of its intended target, making good Septoria control more difficult to achieve."

The situation is confused further by the fact that there's been an increased use of T0 sprays, so that many wheat crops have received two applications before the target stage, she adds.

"There are many factors to consider at T1," agrees Dr Turner. "But there is a real danger that in being careful, farmers are missing the target. The trigger is too often the visual sighting of the disease, rather than the growth stage of the crop."

She reminds growers that the role of the T0 spray is to reduce inoculum, while the T1 spray should be made to control disease on leaf 3 and to provide a foundation for protection of leaf 2.

"The temptation is to go on with your fungicide to coincide with the critical PGR timing at GS31," acknowledges Dr Turner. "But unless you are using a fungicide with the persistence to protect emerging leaf layers, which we suspect Proline does, you run the risk of compromising disease control."

Over the past three seasons the typical date for leaf three fully emerged is the first week of May, so this is the optimum time for the T1 spray, she notes. "Growers are good at following disease control programmes. The challenge for some of them this season is to make sure that they are hitting the correct target at T1."

Her colleague, Dr Steve Parker, agrees. "Part of the problem for growers is that the Septoria risk is not the same every year. Unfortunately growers haven't had access to reliable information that would allow them to respond to seasonal risks, instead they're using set fungicide programmes to balance the risk across seasons."

Judging the risk from disease observations is misleading with Septoria, warns Dr Parker. "The amount of the disease present tells you nothing, especially coming up to T1."

Temperature and rainfall drive Septoria epidemics, he reveals. "We are working on an early warning model with Rothamsted Research, which is being tested on Crop Monitor this year. This will allow us to measure whether rainfall and temperature have favoured or suppressed disease build-up through winter and early spring."

Dr Alison Daniels of Bayer CropScience notes that the introduction of Proline last year helped growers with their T1 timing dilemma.

"Proline's long term protectant activity helps with spray timings," she says. "Its ability to work on the emerging leaf layers is a lifeline to growers with large acreages to cover with one sprayer."

Yield benefits of 0.24t/ha were recorded in Septoria trials in 2005, where Proline was compared to epoxiconazole, she reports.

"We recommend adding chlorothalonil for Septoria resistance management reasons where you're using 0.4-0.6l/ha," concludes Dr Daniels. "But at the full label rate of 0.8l/ha, there's no need for anything else."

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