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Is it time for a T0 rethink?

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UPL is a global provider of sustainable agriculture products and solutions. We are a purpose-led company. As one of the largest agriculture solutions companies worldwide, our robust portfolio consists of biologicals and traditional crop protection solutions.

The loss of key fungicides like chlorothalonil has significantly impacted the early-season wheat disease management landscape.

This, coupled with the emergence of plant health elicitors as a new tool for disease management, has prompted agronomists and experts to reconsider the role of T0 fungicides in disease programmes.

T0 is typically applied at growth stage 30 onto a fully emerged leaf four. While this leaf may contribute little to the final yield, a heavily infected leaf four facilitates the spread of septoria and yellow rust up the canopy, leaving agronomists and farmers chasing disease for the rest of the season.

Until its revocation, chlorothalonil (CTL) dominated T0 product choice. A cheap protectant fungicide with a low resistance risk and highly active on septoria, it fitted the bill perfectly.

By physically acting on the disease to protect the leaf, it also worked in a way that suited how fungicides are used through the rest of the programme.

Plant health elicitors

A new type of product has emerged that could not only fill the gap left by CTL but change how the industry perceives the role of T0 in disease control programmes.

These are plant health elicitors, and they work by stimulating the plant’s own defence mechanisms before an infection has taken place.

Once applied they move throughout the whole plant, negating the need to reapply an elicitor on newly emerged leaves.

Presently, the most popular elicitor is Iodus (laminarin). Derived from a natural plant extract, Iodus mimics the degraded cellular material released from a fungal attack, which activates nearby cells’ defence systems.

Applying Iodus before a fungal pathogen attacks the plant prepares it for when an actual infection occurs.

“A litre of CTL at T0 gave farmers three to four weeks protection of leaf four and dampened down any existing infections in the crop, giving flexibility for the T1 application,” says Stuart Jackson, head of technical services at UPL.

“However, when leaf three emerged, it was completely unprotected until the T1 was applied because the CTL wouldn’t transfer onto it.

“The key difference with laminarin (the active in Iodus) at T0 is you already have the protection on the newly emerged leaf. Once you apply it at T0, the active moves through the whole plant and tells leaves three, two and the flag leaf, hidden in the sheath, to prepare for an infection.

“Iodus provides a benefit to disease control throughout the entire programme. Fungicide timings will be challenging on the variable crops we have this year, but farmers can get a bit more leeway if they know they have already done something to prime a newly emerged leaf’s defence.”

ADAS trials

Last year, the effect of Iodus at T0 on following fungicide programmes was analysed in trials conducted by ADAS near their Rosemaund site in Herefordshire.

The trials compared the activity of Iodus at T0 and Thiopron (sulphur) mixed with the T1 in two different situations, investigating whether the rate of the T1 fungicide can be reduced following Iodus at T0 or including Thiopron in the tank mix.

Ella Bradfield, crop pathology consultant for ADAS, oversaw the work and explains how one trial was high pressure, using the variety Elation, which is highly susceptible to septoria and was sown on the 28 September to increase the exposure to disease.

The other was a more typical commercial situation using Graham sown on the 13 October.

Ella Bradfield

Ella Bradfield © UPL Europe

“In the Elation, we had an average of 56% disease across leaves 1, 2 and 3 in the untreated on the 13th of June,” says Ella.

“There was a good dose response to the different Ascra Xpro (bixafen + fluopyram + prothioconazole) rates used at T1.

“Adding Iodus at T0 improved disease control, especially at the lower doses (of Ascra Xpro).

“Adding Thiopron (sulphur) at T1 lowers the septoria pressure further still, particularly at the lower doses of Ascra Xpro.

“The curves on the yield graph showed that adding Iodus and Thiopron had a benefit of about 0.2 to 0.3 T/Ha.

“We calculated the margin using wheat at £200 /T and the approximate costs of the products used, and this pulled the results out even further.”

Although the trial on the Graham had less disease, with the untreated leaves having 34% disease across leaves one, two and three on the 20 June, there was a clearer difference in the disease control improvement by adding Iodus at T0 and Thiopron at T1.

However, this benefit was not as clearly shown in yield in this trial, explains Ella.

This season, the ADAS team at Rosemaund are repeating the trial but comparing the benefit of Iodus at T0 across Champion, KWS Dawsum and LG Skyscraper at the same site.

They hope that it will pull out the benefit of plant health elicitors depending on the disease resistance of the variety.