Cold hasn’t dented T0 fungicide need

Rising septoria and yellow rust concerns are likely to make T0s a popular option this spring. Mike Abram reports

The coldest winter for many years hasn’t dented enthusiasm for applying T0 sprays this spring. Both septoria and yellow rust are still seen to be a sufficient threat to make the spray more than worthwhile.

Yellow rust, in particular, has agronomists worried. UAP‘s Chris Bean saw “terrible” infections in Viscount before Christmas. “The comments from the experts say it has not been cold enough to stop yellow rust – you almost need plant death for that – just maybe delay it.

“But 10 days ago, it looked like it was about to begin sporulating again, so I don’t think it has gone away,” he told Crops in early March.

Yellow rust hadn’t been seen pre-Christmas since the days of Slepjner, Bob Mills of Frontier Agriculture noted. “The cold weather slowed it down, but you can still find it, so it is all there to come back.”

Agrovista’s Chris Martin had also seen yellow rust in crops pre-Christmas. “I haven’t seen any since, but there is a lot of septoria on older leaves.”

Septoria was a concern in Lincolnshire for Hutchison‘s Dick Neale and in Hampshire for AICC member Steve Cook. “There’s plenty of lesions on Solstice, particularly on early sowings. They are not moving because it is so cold, but there has been rain to spread it,” Mr Cook said.

Fortunately most T0 spray options should cover both diseases, Mr Neale said. “A triazole plus chlorothalonil mix will pick up both. From a T0 perspective I can’t think of a triazole that won’t do a job on both.”

A main concern for growers is whether Atlantis or Pacifica (both mesosulfuron + iodosulfuron) applications will coincide with T0 sprays. That is looking increasingly likely with the growth that is needed for good blackgrass control slow to start this spring.

T0s were likely to be needed from around the last week of March, most agronomists agreed. “It is looking more likely Pacifica and Atlantis will coincide with T0s, and mixing chlorothalonil with them is forbidden by Bayer,” Mr Bean said.

Focus on grassweed management, Mr Neale stressed. He wants to apply Atlantis plus a residual herbicide – as grassweeds are still small – separately. Mixing the residual forced him down the two spray route, he said. “By doing that mix there are no supported tank mixes with any triazole.”

Most agronomists would like to keep the two applications separate if possible, but there are triazole fungicide only options available. “I’m fairly relaxed,” Mr Mills said. “It might mean increasing triazole rates slightly and saving the chlorothalonil for T1.”

He is also contemplating using a strobilurin fungicide on light land at T0 if yellow rust is particularly active at spraying. “It is not something I’ve ever done before, partly because of cost, but there are some mixtures available, such as Asana (kresoxim-methyl + epoxiconazole + fenpropimorph), that might be useful if rust kicks off.”

Most agronomists also appear to be considering using a strobilurin at T1 too, which for most is a departure from the usual T2 / T3 use for the chemistry.

Strobilurins were becoming less applicable at T3 with more focus on fusarium control, Mr Mills pointed out. “There would be benefits for using them at T1 for yellow rust.”

And if brown rust did make an appearance early, then a strobilurin would be a must, Mr Bean added.

T0 strategy 

Yellow rust and septoria concerns

Triazole + chlorothalonil preferred choice

Grassweed control may interfere with chlorothalonil use

Timing likely to be from end of March