2018 - Making the case for T1.5 applications in wheat
Throughout the season, we’ve been extolling the virtues and benefits of applying a T1.5 treatment to protect Leaf 2 in wheat from the ongoing threat from septoria. In this hub update, we’ll use the benefit of hindsight to focus on why a T1.5 application is still relevant following the late and wet start to spring.
At all stages in a wheat crop’s development, the most effective way of controlling septoria is to prevent infection from occurring in the first place. This means ensuring each newly emerged leaf is protected prior to the first infection period – in essence, before the first spores land on the leaf and germinate.
Whilst Leaf 3 and the flag leaf (Leaf 1) are routinely protected at T1 and T2 respectively, Leaf 2 often goes unprotected at its emergence, with growers relying on the subsequent T2 application to give kickback curative activity against any existing infection. Unfortunately, this strategy puts Leaf 2 at significant risk of the infection progressing beyond chemical control, especially if the T2 application is delayed and because the curative activity of some chemistries has been eroded by increasing disease resistance.
Growers should therefore consider the concept of ‘Leaf Layering’ (applying protection to each new leaf as it emerges) to ensure optimum protection of ‘at risk’ crops such as those which were drilled early, drilled using a septoria susceptible variety or located in areas prone to septoria infection. For Leaf 2, this means applying a T1.5 treatment at GS33 to treat the fully emerged leaf.
In many cases, this season’s spray timings have been hampered, interrupted and impinged by the late start to the spring and wet ground conditions. For some growers, that has meant an abandonment of plans to apply a T0 spray, with the ensuing T1 treatment being bolstered to make up for the lost spray opportunity. The danger in this scenario is that the T1 treatment may have pulled forward and applied ahead of the ideal growth stage. Where this has happened, there is a risk that the ensuing gap between T1 and T2 could become extended, thereby leaving Leaf 2 unprotected for too long.
In other cases, the loss of the T0 timing may have left crops lacking a PGR treatment, with the subsequent T1 spray being used as an opportunity to make up for the missed application. Where crops have grown rapidly through their growth stages, especially in high fertility situations, growers in this position might also be inclined to go in with a T1.5 PGR application: where this is the case, it may make sense to kill two birds with one stone by piggy-backing the T1.5 PGR application with a suitable septoria fungicide.
What to use at T1.5
The first choice of active ingredient for any T1.5 treatment where septoria is the driver should be a multi-site such as folpet as this will provide good levels of contact protection against septoria, and can be mixed with a strobilurin to protect against the threat of rust, or an azole if active rust is present.
Folpet also takes the pressure of resistance off azoles and SDHIs: field trials and septoria strain analyses conducted in 2014 have shown that the addition of folpet to an azole stopped the selection of resistant septoria strains, preventing any further slippage in fungicide performance. Similar results were also seen in 2015 trials carried out on SDHIs. Folpet has also been proven not to interfere with the curative kickback activity of partner azoles or SDHIs.
Applying a multi-site at T1.5 will therefore ensure the newly emerged Leaf 2 is protected from septoria infection, thereby moving away from the reliance on the curative activity from T2 applications to control any latent infection and the risks associated with allowing the disease to get away. With the current arsenal of fungicides having a reduced curative capacity this will not only ensure the crop remains cleaner for longer, but will also take the pressure off subsequent application timings.
Folpet is available as Arizona (500g/l folpet SC) as a flexible mixing partner, and Manitoba where it is co-formulated with a leading azole (50g/l epoxiconazole + 375g/l folpet SC). In both cases, Arizona and Manitoba are based on tried, tested and proven formulations with both offering broad spectrum flexible disease control for cereal crops.