It’s a new era for winter wheat fungicide options as we say goodbye to an old reliable

Fungicide options for winter wheat are like a revolving door: as we gain some exciting new products, we are losing many more. But while the products may come and go, accurate spray timings are still key to disease control in wheat.

Disagreeable weather last autumn resulted in a prolonged sowing period from early October to February, so there are large variations in leaf emergence in winter wheat crops across the country.

Thorough examination of the crop is essential to correctly timing the upcoming flag leaf application.

Many growers discovered that there can be large variations in leaf emergence, even within fields, when recently applying the Leaf 3 fungicide.

It is well established that fungicide application on fully emerged Leaf 3 and Leaf 1 are the crucial timings to maximise the return from fungicides in the control of septoria.

Applying a fungicide to a flag leaf that is not fully emerged will leave a portion of the leaf unprotected as the fungicide moves towards the tip of the leaf.

A late application will result in an undesirable period of exposure to infection from the lower canopy.

Revysol is new this year and is the first azole to the market since prothioconazole (Proline) in 2005.

Essentially it is a new molecule from an old family, but a major difference to existing azoles is the presence of what is called an isopropanol linker. This allows the molecule to bend to fit the target pathogen.

Revysol currently controls known azole mutations.

It will be sold in a mixture with the SDHI Xemium in two products, Revystar and Lentyma.

This year we have also had the registration of a new active Inatreq, which has both protectant and curative activity against septoria. While not available for this season, it represents a significant new tool for the future in the battle against septoria.

The use of chlorothalonil is no longer permitted after May 20. Most growers will have used chlorothalonil with the Leaf 3 application and it is recommended to use it on crops that will receive Leaf 1 application before May 20.

The multi-site activity of chlorothalonil has been a key measure in slowing the development of resistance, in addition to septoria control.

The nature of crops this year means that some crops will not have Leaf 1 fully emerged by May 20, so an alternative multisite like Folpet (Arizona) should be used as an anti-resistance strategy to protect our new and existing all chemistry.

Teagasc have been trialling Revysol-based fungicides over the last few seasons, and while levels of disease have varied between seasons, Reyvsol has performed consistently.

Although it is a clear step up on existing standards, the availability of chlorothalonil until May 20 means that with careful consideration to disease pressure and timings, other wheat fungicides remain viable options for those crops that may receive their Leaf 1 application before this date.

However, in these cases an assessment of the risk posed by septoria must be taken. For instance, how much curativity is required? Has the weather in the preceding weeks being conducive to the spread of the disease, as it is in these cases where the strength of Revysol will become apparent.

The use of anti-resistance strategies that will prolong the activity of existing chemistry and delay the inevitable development of resistance to new products are essential to all fungicide programmes.

These strategies include:

The choice and amount of fungicides applied must reflect the risks posed by the disease(s)

Always use a mix of different modes of action with activity against septoria;

Always include a multi-site

Use by date:

Farmers are advised that there are a large number of products that need to be used up this year fungicide eg. Folpet, Chlorothalonil (before May 20);

Where possible the azole component of the SDHI mixture should be alternated between groupings at the key septoria applications at Leaf 3 and Leaf 1 (e.g. azole groupings: epoxiconazole & prothioconazole versus metconazole & tebuconazole).

Although Revysol appears not to be impacted by current mutations that affect other azoles, the above measures of limiting usage, mixing with effective partners and including a multisite are essential to retaining its efficacy.

Products in use up in 2020

There are a significant number of products in use up this year. It is important to check your spray store to ensure that all products are used by their last date of use.

The table (left) lists a selection of the main products used on farm which have a use up date in 2020. For further details check the PCRD website.

Ciaran Collins is a Teagasc crop specialist based in Moorepark, Co Cork