How to manage septoria disease in wheat


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That makes attention to detail more important than product choice, he believes. “We have the tools to manage septoria, even though the disease is mutating.

“But getting behind with spraying is the worst thing you can do. It’s better to be a day or two early than a day or two late.”

Spray timings

  • T0 – protects leaf 4 – GS30 (or about two to four weeks before the T1 spray)
  • T1 – protects leaf 3 – GS31-32
  • T2 – protects leaf 1 (flag leaf) – GS39
  • T3 – protects the ear – GS61-65

Fungicides

The septoria fungicide toolbox is limited to three main groups: the azoles, the SDHIs and multi-sites.

Of those, the azoles have seen the biggest decline in performance, with their eradicant control dropping by over 60% since they were introduced. Despite the discovery of a few insensitive strains in 2016, the SDHIs are still giving good control in the field.

The multi-sites, which have been in use for many years, remain unaffected and have a low risk of resistance.

Other chemistry, such as the morpholines, can have some effect on the disease, but are not active enough against septoria to be used as a key component of a septoria strategy.

However, the strobilurins are ineffective against septoria, due to widespread resistance.

Given the developing situation with resistance and the complex nature of the disease, the multi-site fungicides are a vital tool for septoria management.

According to Jonathan Blake, principal research scientist at ADAS, they should be the first product into the tank at both T1 and T2 when it comes to septoria and should also form the backbone of any resistance management strategy.

“Chlorothalonil is an essential component. Although it can have negative effects on the curative activity of all products, the benefits of it outweigh any negatives.”

The T0 spray does very little for septoria control and it is rare to see a benefit from it where this disease is concerned if the T1 and T2 sprays are applied correctly, he notes.

“For other diseases, the T0 is more important and offers some insurance. But with septoria, the T1 and T2 timings are the main ones.”

Filling up a sprayer © Tim Scrivener

© Tim Scrivener

For Mr Sparling, the T0 spray acts as a holding treatment and buys some time if there are any subsequent delays, so he will often make use of chlorothalonil and a strobilurin at this stage. However, he accepts that the T1 and T2 sprays are more critical with septoria.

“Getting those two right is really important. The other spray timings are just frittering about at the edges.”

Bill Clark, technical director of Niab Tag, notes that there won’t be a yield response from a T0 in most years.

“But it offers some help if you don’t get the T1 spray right, so it gets applied for the flexibility it brings.”

Including an SDHI at T1

While most field situations will warrant the use of an SDHI at T2 in a three-way mix, the more difficult decisions about product choice come earlier in the season at T1, believes Dr Blake.

“The worst thing to do is to apply an SDHI where it is not needed, so try and keep two applications of SDHIs as the exception,” he says.

“At T1, an azole plus chlorothalonil mix may be adequate.”

However, growers in the West with susceptible varieties are likely to see a benefit from including an SDHI at T1, while others will do it for risk management purposes, he accepts.

At T2, it’s worth using all the firepower on offer, believes Mr Sparling, who will be planning to use one of the best SDHI products with a high rate of triazole.

“And if it’s a bad spring for septoria, I will have no hesitation in recommended an SDHI at T1 too.”

He advises growers to look at what they’re getting for their money.

Spraying T1 in wheat © Tim Scrivener

© Tim Scrivener

“There is more choice of SDHIs than ever, which then need to be partnered with either prothioconazole or epoxiconazole at a rate of 80-100%.

“There’s no need to be spending crazy amounts on fungicide programmes, but quibbling over an extra £3-£4 at the flag leaf timing is a false economy and pointless.”

If septoria control needs topping up at T3, an azole will do the job, with prothioconazole and tebuconazole being the main contenders.

Finally, all fungicide programmes used on wheat in 2017 must adhere to the guidelines on resistance management.

High-risk practices are thought to accelerate declines in sensitivity to both triazole and SDHI fungicides.

(Source – http://www.fwi.co.uk/arable/how-to-manage-septoria-disease-in-wheat.htm)

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