Laying the Foundation for Healthy Crops – David Ellerton - Farmers Guardian

Posted on

A well planned T0 fungicide can buy time and reduce pressure on subsequent sprays.

T0 fungicide tips:

  • Septoria remains top priority
  • Early protectant control reduces curative pressure on later sprays
  • Include a multi-site active as routine
  • Plan sprays/tank mixes according to varietal susceptibility and disease pressure
  • Consider rust mildew
  • Use a range of chemistry for resistance management 

The importance of a T0 spray can sometimes be overshadowed by later TI and T2 fungicides, but it is important for controlling disease established over winter. It also buys time and reduces pressure on subsequent sprays, so has valuable benefits even where disease pressure appears low, according to Hutchinsons.

T0 timing is not directly determined by growth stage, although fungicides are typically applied from late tillering to the start of stem extension (GS25-30). A slightly earlier spray may be required if disease pressure is high, particularly from yellow rust.

Fungicide choice depends on many factors, such as variety susceptibility, local conditions and diseases present, but generally septoria remains the priority in most situations, says Hutchinsons technical director David Ellerton.

"Fungicides do not have the curative control they once did, so we cannot let septoria get established and end up in a curative situation by T1. Once septoria is established it is very hard to take out.

"A multi-site protectant is cost-effective and I believe should be routine at T0 to protect leaf 4 and give leeway to following fungicide applications should weather delay Tl sprays."

Chlorothalonil is the strongest on septoria, however, folpet offers a good alternative with a slight edge against rust, he says.

Septoria Risk

South west England suffers particularly high septoria risk, which is why Hutchinsons agronomist Ryan Came-Johnson puts more emphasis on the T0 fungicide for wheat crops across his region around the Cornwall and Devon border.

"Because the pressure is so high in this area, we have got to keep septoria out from the start, otherwise it can cause real problems."

In last year's mild season, that meant an 'extraordinarily early T0 spray applied in mid-February to some of the most forward crops, however, this year is looking more normal.

"A lot of crops were drilled later this season and the weather has not been as mild as last year, so wheat is not as advanced (as in 2017). Most crops look fairly clean at the moment because we have not got the lush growth and warm, damp microclimate within the canopy for septoria to develop. However, a lot depends on the weather."

He too favours a chlorothalonil base to T0 sprays, with a chlormequat-based growth regulator if required. Other actives may be included for specific diseases such as mildew, he says.

Mildew and yellow rust are the other main targets at T0, especially when growing susceptible varieties, or in particularly high-risk situations.

For curative mildew control, fenpropimorph or cyflufenamid should be included with the T0.

In protectant situations in high risk areas, for example western England, Scotland, on organic soils, or with susceptible varieties, consider proquinazid, Dr Ellerton says.

Where rust pressure is high and curative control is required, a rust-active triazole should be included at T0, such as tebuconazole, cyproconazole or epoxiconazole, he adds.

Even where a variety has adult resistance, this often does not kick in until later in the season when the damage to yield may already be done.

"If it is a new strain of rust, varietal resistance may be overcome altogether. So if yellow rust is present, it pays to knock it out early when it is relatively easy to control," says Dr Ellerton.

Strobilurins such as pyraclostrobin or azoxystrobin are another option in protectant situations which can reduce reliance on azole chemistry and potentially benefit rooting and nitrogen scavenging, he adds.

"Strobilurins do not have the curative action which triazoles offer, but they can be a good alternative, especially if triazoles are going to be used at later timings. The rooting benefits may be particularly useful on more backward crops or drought prone soils."