T3 serves multiple roles in high pressure year

Of all the main fungicides, the growth stage 63-65 (T3) treatment is sometimes where growers might look to make savings, but in a season like this, that could be very risky, says the firm’s head of integrated crop management, David Howard.

The T3 is the main fungicide for protecting ears against fusarium infection, and while that risk is largely determined by rainfall between ear emergence and harvest, recent heavy rainfall is likely to have increased pressure by splashing spores further up the canopy making ear infection easier, he warns.

Accurate timing of ear sprays is critical to their efficacy, and Mr Howard says they should ideally be applied as soon as ear emergence is complete and flowering is underway (GS 63-65) to give the best control of fusarium (favoured by warm and wet conditions during flowering) and/or microdochium (cool and wet).

But with very variable crop growth this year, accentuated by unsettled weather, fluctuating temperatures, and low sunlight during March, April and May, ear emergence is likely to be variable and protracted, so extra care will be needed to hit the optimum spray timing.

“Delaying the T3 application, even if the T2 has only recently been applied, will result in poor ear disease control, particularly once flowering is coming to an end (GS 69). Accurate timing on-farm is a huge practical challenge given that flowering occurs once ears are out and before florets are visible, and in practice it is better to be a little early than a little late.”

To help predict fusarium pressure, Mr Howard recommends growers complete the AHDB mycotoxin risk assessment, which gives a risk score based on seven factors; region, previous crop, cultivation, varietal resistance rating, T3 fungicide application, and total rainfall during flowering and pre-harvest.

This also allows completion of Section 5 of the Combinable Crops Passport (essential to marketing grain) assessing the risk of breaching the limits for mycotoxins in grain.

Several factors must be considered when deciding on the most appropriate fungicide options at T3, including varietal susceptibility, presence of disease, chemistry used at T2, and weather forecast from ear emergence to flowering, says Mr Howard.

For fusarium species, he says metconazole, prothioconazole or tebuconazole all offer good control, leading to reductions in DON mycotoxins. He notes that AHDB and ADAS trials suggest better results from prothioconazole + tebuconazole mixtures and formulations compared to straights of either active.

“Adding phosphites (e.g. Advance 66 or Phorce) at ear emergence has also been found to reduce DON production.”

Metconazole, or tebuconazole-based products are also strong on yellow and brown rusts, he says.

Prothioconazole is the main choice for managing Microdochium nivale, which although does not produce mycotoxins, can still have a significant yield impact. Ideally prothioconazole should be used with fluoxastrobin or tebuconazole, which would add some Septoria control where growers have already reached the maximum number of SDHIs allowed in the programme.

“If Septoria pressure is high and crops have not received two SDHI’s, then ear sprays could include an SDHI, such as bixafen/ Fluopyram+ prothioconazole/tebuconazole, fluxapyroxad + metconazole, or benzovindiflupyr + prothioconazole, where rust pressure is expected. Similarly, if Fenpicoxamid has not already been used in the program then Fenpicoxamid + prothioconazole would make a very strong Septoria option.”

Strobilurins, such as fluoxastrobin, pyraclostrobin or azoxystrobin, could be considered for added control of rusts, Septoria nodorum, and sooty moulds, he notes. They may also deliver a yield benefit through improved green leaf area retention and better stress resilience, however strobilurins must be applied with a fungicide with a different mode of action, and as with SDHIs, only two strobilurins are allowed in any crop fungicide programme, he advises.