April Crystal Ball Time – By Roger Bryan

With the main fungicide timings rapidly approaching, it’s a good idea to take stock of where we are with the main wheat cereal diseases, fungicides available and current known resistance.

As usual, wheat has come out of the winter with plenty of Septoria on the older leaves so nothing new there. What is surprising is the apparent (as of 3^rd April) absence of yellow rust in Southern counties, even on the most susceptible varieties such as Zyatt & Skyfall. Has there been another shift in the most abundant race of yellow rust out there?? All will become apparent in time no doubt.

At least that has taken some pressure off the traditional T0 fungicide timings which have been delayed by the monsoon March weather which delivered over 150mm (6’’) rain.

There is still no panic over Septoria as final leaf 4, whist having no doubt been badly infected by rain splash, is not a big player in delivering yield. However, it does put a dirty leaf close to the first important leaf now emerging, that being leaf 3. A dry April could still put a halt to a potential Septoria epidemic. The frosts in February and wet March have stopped brown rust for now and mildew is confined to lush crops and valley bottoms. However, eyespot levels will have been cranked up by the rainfall so varieties like Crusoe, Graham and Extase will need checking.

The fungicide choices for Septoria this season are limited to 3 active ingredients plus folpet (Arizona) as the only multisite option. Mefentrifluconazole partnered with the SDHI Fluxapyroxad in Revystar is the only triazole these days with significant protectant activity on Septoria, and decent rates are required under high pressure. The new active Fenpicoxamid, partnered with Prothioconazole in Univoq is technically the superior Septoria product. But following the first year of it’s use, there are questions over the formulation effect on sprayer parts even though the damage caused seemed random. The 3^rd product to consider has been around a bit longer, Ascra, a decent slug of Prothioconazole plus the double SDHI’s Bixafen and Fluopyram, seems to be holding up better than expected but would be ranked in third place to the two products above.

There are some significant prices rises on ag-chem products this season, unfortunately fungicides have not been immune to this. Ensuring the right product is used to safe guard yield and generate the biggest return on investment will be more important than ever this season.

Following the loss of chlorothalonil (Bravo) the traditional T0 timing for targeting Septoria is rarely justified and fungicide choice for Septoria at this timing is really limited only to folpet. Instead the focus of the T0 timing has moved to targeting yellow rust on susceptible varieties, using the two rust actives tebuconazole and strobilurins. Yellow rust might be absent now but who knows what’s around the corner?

At T1, Ascra is a good all-rounder with good activity on eyespot as well as Septoria and rusts. However, under the most severe Septoria pressure; September sown, susceptible variety and a wet April, Revystar is technically the better choice at T1. All should be applied with folpet as the multi-site to add variety to the fungicide programme to counter the complication of resistant strains of Septoria.

Timing is always the issue at T1 when leaf 3 emergence is protracted across the tillers of individual wheat plants. The majority of leaf 3’s need to be emerged to get the most bang for your buck. The most forward tillers have leaf 3 emerging now (3^rd April) but the T1 should not be applied for 10-14 days to allow the later tillers to emerge. That is where chlorothalonil used to be so useful as it could be physically redistributed about the plant. This is less of the case with folpet.

At T2, Univoq or Revystar are preferred. On more resistant varieties such as Extase, Mayflower, Palladium and Theodore, Ascra would be fine provided those varieties have not been September sown. Which most have. All three products are ok on yellow rust and Revystar has the edge on brown rust so a strobilurin such as Comet at T2 or T3 may have to be added. As will folpet if the Septoria pressure around T2 is high. Just a reminder that following some of the problems last season Corteva have issued updated guidelines on the use of Univoq this season, link below:

https://www.corteva.co.uk/tools-and-advice/stewardship/inatreq.html

It is also worth remembering that there is very little curative activity these days from any of the above active ingredients. Even with the superior Univoq, we are only talking just a few days kick back. So, if your timings are running late due to weather delays, don’t expect miracles. Weather forecasts are only reliable for 5 days ahead, so it makes planning your fungicide programme a tad tricky.

The T3, early flower treatment can be 2 weeks after the T2 flag leaf spray. The T3 is all about fusarium and michrodocium ear blight prevention. The risk is highest when wet during wheat flowering and is particularly important for milling wheat varieties to keep potential mycotoxins as low as possible. Prothioconazole (Proline) and tebuconazole are the key actives here. The Septoria horse has bolted by the T3 timing but keeping rusts under control is critical so strobilurins can have a role to play. Provided only one SDHI has been used, Elatus Era is also a good T3 option with rust activity.

All will be revealed very shortly. With less than 40 days to flag leaf emergence, there seems a lot of field work to be done.

But it always gets done, one way or the other!