1 April 2000

Tee off with T1

Its time for the T1 spray already and its going to have to last. Tom Allen-Stevens finds out what to put on and how to get the timing right.

TIMING will be the key factor for getting the most out of your T1 fungicide, and this year it will probably go on early. Thats the message from UAPs western technical manager, Peter Gould. Hes been busy in the UAP trial plots, regularly dissecting plants in order to identify when the key timings are occurring.

"Leaf three emergence is when the T1 fungicide wants to go on, which occurs at or just after terminal spikelet (around GS31). This year thats likely to happen earlier due to many growers drilling at the beginning of September and the warm autumn and winter weve had."

So for early-drilled crops, leaf three could be coming out now, or could already have emerged. But how do you know if your crops at this crucial stage? "Youve got to pull the leaves back and dissect the plant, its the only reliable way to tell. The ear will still be wrapped inside leaf two and the flag leaf," says Mr Gould.

For later-drilled crops theres likely to be less urgency to get the sprayer out. Mr Gould estimates that for wheats that were drilled in mid-October, leaf three emergence is likely to come in mid to late April. But he warns its a good idea to err on the side of caution: "Its better to be a week too early than a week too late."

And why is leaf three so crucial? "The lower seed rates growers have adopted are making a more open canopy. So more light gets to the lower leaves and strobilurin chemistry ensures these are greener for longer. This means the lower leaves will be contributing more to the final yield." Recent trials have shown leaf three in open crops contribute 12% of the final yield, compared to 8% in dense crops.

The protectant activity of strobilurins means they need to be sprayed before a disease takes hold or a higher rate of curative triazole would have to be included. Keeping leaf three clean also reduces the risk to the emerging leaf two and flag leaf. The timing of flag leaf emergence is irrespective of drilling date, Mr Gould points out, so a robust mixture is needed to span the increasing gap between T1 and T2 timings.

His choice for the T1 slot is Landmark (kresoxim-methyl + epoxiconazole). The main disease threat is septoria in the west, but eyespot can also be a problem, especially on second wheats. "Landmark has a good activity against eyespot and is a good, natural T1. On second wheats take-all often makes the effect of eyespot worse. If take-all is going to cap your yield and youd rather not use a strob, use Unix (cyprodinil) instead."

Growers should also be on the look out for mildew and yellow rust, advises Mr Gould. Claire and Hereward are susceptible varieties for mildew, especially in sheltered fields. Savannah is particularly at risk to yellow rust.

Rate of Landmark on early-drilled crops will need to be about 0.75 litre/ha, believes Mr Gould. On later-drilled crops this can be dropped to 0.5 litre/ha with a quarter rate of Opus (epoxiconazole) added in to get better kickback if the application is delayed in high disease situations.

"Growers should aim to apply the T2 spray early as well, just as the flag leaf is emerging. You can ring the changes at T2. I dont see a place for Amistar (azoxystrobin) or Twist (trifloxystrobin) at T1, but at T2 either of these mixed with Caramba (metconazole) should give good persistence."

Rhynchosporium is the main disease in barley and if you can see lesions in susceptible varieties Mr Goulds advice is to spray at T0 (GS30). Most at risk are Halcyon, Pipkin, Regina and Heligan. 0.75kg/ha Radius (cyproconazole + cyprodinil) or Unix is Mr Goulds prescription with 0.25-0.5l/ha of Amistar.

Unix is slightly cheaper and covers eyespot, but he recommends sticking to Radius if the rhynchosporium and rust are bad and raising the rate to 1kg/ha. This should go on at the end of March for fast-developing varieties, like Pearl and Regina or first week of April for slower varieties like Fanfare, Halcyon and Pipkin.

Watching out for mildew in north…

NORTHERN independent agronomist Simon Senior has both mildew and septoria in his sights for the T1 spray. Mildew could pose more of a threat than in previous years: "Normally it comes and goes as spring temperatures fluctuate. This year conditions are mild so there could be more emphasis on mildew control."

Normally a half rate of Landmark would be his recommendation, but he has not seen much eyespot this year, so is steering towards strobilurins that will focus more on the mildew. "A half rate of Twist mixed with a half rate of Folicur (tebuconazole) or Opus would do well, providing you get into the crop before the disease gets established. If that is not the case, increase the rate."

Timing depends mainly on drilling date. Some of his earliest crops have received a very early dose of fungicide, but on the whole most will be ready at the beginning of April. But he believes there will be less rush where the seed was dressed with Baytan (fuberidazole + triadimenol). Later drilled wheats can wait until late April.

…but receding in the east

Norfolk-based AICC agronomist John Purslow believes theres no blueprint for disease control; it must be tailored to variety and drilling date. He also advises growers that, with wheat at £60/t, a T1 spray could be unnecessary.

"Claire and Genghis, for example, are very resistant varieties. Their response to a T1 spray is minimal, apart from mildew," he advises. He noticed a lot of mildew early on, although it does now seem to be receding. A dose of Fortress (quinoxyfen), with rate depending on disease pressure, should be sufficient to clear up the mildew on these sorts of resistant varieties, he says.

More susceptible varieties, like Consort and Riband, would benefit from a slightly more robust T1, Opus and Bravo (chlorothalonil) being Mr Purslows choice. But he still believes spending money on strobilurins is best left until flag leaf. Only in dense crops with a high disease pressure would he recommend using Landmark at T1.