Robust T2 can ease pressure on T3 top-up in Septoria season

• Variable ear emergence in crops

• Improve green leaf area retention

• Protect grain until end of season

Growers are being encouraged to plan their T3 sprays carefully with wheat under relatively high pressure from Septoria this spring.

Variations in ear emergence can complicate the optimum T3 fungicide timing, says David Howard, head of integrated crop management at agronomists Hutchinsons.

“It’s very rare for all ears to emerge at the same time, and with warmer than average temperatures through autumn into spring, some crops have raced through growth stages, so ear timing could be variable depending on variety, drilling date, and other factors.”

Mr Howard reinforces the case for using a T3 fungicide, especially as recent years have shown that disease pressure – septoria, yellow rust, or brown rust – towards the backend of the season is often much greater than expected.

“We must protect the main yield-building leaves as long as possible beyond the main T1 and T2 fungicide timings, while safeguarding grain quality. Crops can be quite exposed if the weather changes rapidly at the end of the season.”

Fungicide options

Before applying T3s, growers should complete an AHDB mycotoxin risk assessment. Legal limits cover fusarium mycotoxins, deoxynivalenol (DON) and zearalenone (ZON) in wheat intended for human consumption – and there are guidance limits for feed grain.

To manage fusarium – favoured by warm and wet conditions during flowering – and associated mycotoxins, Mr Howard says metconazole, prothioconazole, or tebuconazole, are all good options.

AHDB research indicates combinations of prothioconazole and tebuconazole are more effective than single actives alone. For controlling microdochium – cool, wet conditions – prothioconazole is preferred.

“Use a good fungicide dose of at least 50% recommended rate,” says Mr Howard.

Including strobilurins, such as azoxystrobin or fluoxastrobin, can be beneficial in either situation, by giving good persistency, helping manage rusts, Septoria nodorum and sooty moulds, and delivering greening benefits.

“Improving green leaf area retention and reducing crop stress can lead to wider yield benefits from the T3 aside from from disease control.”

In contrast to previous dry springs, rainfall throughout March and April was above average across much of the UK. This resulted in high septoria pressure – particularly in earlier-sown wheats.

With favourable conditions for disease development, growers who used a robust flag leaf fungicide will have taken some pressure off T3 sprays – a timing primarily aimed at managing ear diseases.

It is, however, very tricky to fully control both ear and foliar diseases with the T3, as the optimum timings are slightly different, he says.

For managing ear diseases, such as fusarium, microdochium and sooty moulds, there is a narrow window of opportunity to treat crops, around full ear emergence, with flowering just beginning in the middle of the ear, at growth stages 63-65.

Missed timings

“Applying fungicides even just a few days beyond that, means you will start to lose control rapidly, although there will still be benefits to foliar protection.”

If the priority is on protecting the top two leaves from foliar diseases, such as Septoria or rust, the optimum timing is slightly earlier – typically growth stage 59 – but this is too early for any significant effect on ear diseases, advises Mr Howard.

“Using prothioconazole or tebuconazole in programme at this earlier timing has been shown to slow ear diseases, but it’s not effective enough. Growers therefore need to have applied a robust T2 to protect crops through to full ear emergence.”

The strongest curative options at T2 are generally either fluxapyroxad + Mefentrifluconazole, or fenpicoxamid + prothioconazole, says Mr Howard. These should be go-to choices in anything other than a low risk situation, he adds.

Both offer similar Septoria control, so deciding between the two may come down to other factors. Mefentrifluconazole is slightly better on brown rust, while fenpicoxamid has an edge against yellow rust.

Extended protection

Including the multisite folpet can be worthwhile for extending Septoria protection in high pressure situations, and for resistance management.

Of the older chemistry, AHDB research shows a notable drop in the efficacy of some SDHIs that were once the mainstay of T2 programmes. Growers should be aware of the changes when choosing products, especially if curativity is needed.

Mr Howard says there is still a place for actives such as bixafen, Fluopyram + prothioconazole, or other bixafen, Fluopyram mixtures, which have shown higher activity than other SDHIs. But higher rates are required if Septoria pressure is significant.

If rust is the focus, rather than curative Septoria control, Mr Howard says products such as benzovindiflupyr + prothioconazole offer good efficacy – and may deliver some Septoria protection too.