As the all-important T1 and T2 fungicide timings approach, growers are being urged to respect the crucial synergy between varietal resistance and fungicide chemistry when finalising spray decisions.

Last year’s late epidemic of Septoria following a dry start to spring resulted in many wheat varieties with Cougar parentage having their AHDB Recommended List ratings downgraded as new strains took hold, however, the multi-gene resistance of LG Astronomer – a (Leeds x Cougar) x Britannia cross – proved much more resilient, with its three-year rating only dropping slightly to 6.8, thereby retaining its position as one of the highest on the RL’s three-year and one-year ratings.

“Within the Group 3 sector, the newer Limagrain varieties have really upped the game against Septoria compared with older varieties,” says Limagrain UK’s Ron Granger, adding that selecting strong genetics is the number one consideration for tackling Septoria.

Tailoring fungicides

Mr Granger acknowledges there may sometimes be an opportunity to reduce fungicide inputs at T0, especially if growing Cougar-based material that offers good seedling resistance to yellow rust, but he stresses it is vital not to get caught out by any disease as T1 and T2 fungicide programmes may be implicated.

NIAB’s crop protection and agronomy specialist, Aoife O’Driscoll, added that Septoria is an “unbelievably adaptable” pathogen, capable of cycling several times through the season, with an ability to evolve and potentially overcome fungicide chemistry or varietal resistance.

“People often talk about varieties or fungicides ‘breaking down’ to Septoria, but they’re not changing; it’s the pathogen that’s evolving. Cougar isolates were actually first identified in 2015, but it was the perfect conditions for Septoria last year that allowed them to take hold,” she stated, also adding that growing a range of three or four different varieties across the farm can help to reduce the risk of Septoria taking hold.

“In the same way, growing a variety with a more diverse genetic background (such as LG Astronomer) can also make it harder for the pathogen to evolve and overcome that genetic resistance. The more diverse the genetic background, the higher the ‘wall’ that the pathogen has to navigate over.”

Additional benefits

Modern chemistry can also bring physiological benefits to rooting and crop greening that are in addition to disease control. BASF Real Results farm trials of around 30 varieties at five farms support this view, according to Dr Jon Helliwell, cereal fungicides business development manager.

“We’ve seen in these trials that there is a clear yield benefit from stepping up to stronger Revystar-based chemistry at the T1 and T2 timings that goes beyond disease control.”

Further research has reinforced the impact such physiological effects can have on nitrogen use efficiency, with trials showing a clear benefit from using Revystar at almost all nitrogen levels ranging from 37 to 370 kg N/ha.

“Even the strongest varieties should be supported with good chemistry and this is true when you consider that the T1 is expected to offer three to four weeks protection, while asking T2s to protect crops for up to seven or eight weeks.

“If you apply a stronger fungicide, the maximum financial loss you face is the additional cost of that product, whereas if you cut back unnecessarily and get inadequate disease control, the cost could be a lot greater.”