After three and a half months with below average rainfall you wouldn’t think winter wheat crops would be under threat from Septoria but that is the situation for many.
Lush canopies mean some crops are harbouring more disease than initially thought. In some areas the threat has been compounded by T1 applications interrupted by high winds and showers after Easter. Despite low overall precipitation, it can only take a single rain splash event to spread Septoria up the canopy.
AICC agronomist Patrick Stephenson says in North Yorkshire it is very much a ‘mixed bag’. He urges growers think carefully about SDHI and azole rates and ensure they are appropriate for the threat crops are facing. “I wouldn’t assume Septoria won’t threaten. It is present on leaves four and five and with lush canopies for most crops it could transfer via leaf contact to leaf two. Clearly susceptible varieties are most at risk but no variety is immune to the disease.”
A particular concern is where good autumn weed control meant a clean-up was not needed. That combined with low rainfall encouraged growers to not apply a T0 fungicide as well.
In some cases, however, T1 sprays have subsequently been applied before final leaf 3 was fully emerged, while he is also concerned that T1 azole and/or SDHI rates have been cut to accommodate a strob or secondary azole for varieties susceptible to yellow rust, leaving Septoria protection weaker.
“Regardless of why there might have been an early season compromise has occurred it’s almost a given that by the time you get to T2 the Septoria pressure will have amplified. You are relying on dry weather to keep the disease from spreading up from the lower canopy.
“Where T1s have gone on early the gap to T2 could be a little on the long side. Growers will need to look at variety and risk and adapt rates accordingly. I think in high-risk situations full rate azole + SDHI mixes might be necessary, while the complementary effects of bixafen and fluopyram in Ascra (prothioconazole + bixafen + fluopyram) could be very welcome too. SDHIs are our most potent options so two together helps.”
For crops where T1 sprays where applied in good time he would still be looking at azole + SDHI mixes with CTL but he says there should be more flexibility with product and rate.
The rain following Easter has got an ‘upside’, Mr Stephenson says, arriving just in time to protect the potential established earlier in the season. “It really depends on the weather over the next two weeks. Another 10mm of rain and it could really set the season up, but obviously Septoria will need to be managed.”
Bayer’s Ella Crawford points out the top two leaves contribute around 70% to final yield. “These are the yield generating leaves so you must protect these to optimise crop potential. Septoriavisible in the crop at this stage is only a small part of what is actually there and the disease can remain in its symptomless latent phase for up to 28 days.
“At T2 the aim is to protect against the weather and disease present in the plant developing further. The benefit of two complementary SDHIs, such as in Ascra, is that it will give the highest level of protection of the flag leaf and some kick-back on infected leaf two,” she adds.