The importance of controlling speckled leaf blotch at GS32

Around 30-35 years ago, when septoria tritici blotch (SLB, Zymoseptoria tritici) became the key septoria disease of wheat, sweeping aside septoria nodorum blotch (Phaeosphaeria nodorum), many trials were conducted to understand how the disease spreads within the canopy during spring.

Initially it was thought that “rain splash”, when raindrops hit a sporulating lesion and move the spores around the canopy, sometimes for quite a distance, was the way SLB spread. This was possibly/probably the case when tall wheat varieties which had quite widely spaced leaves were popular.

But as shorter wheat varieties became popular it was realised that SLB infections were spreading within the canopy when heavy rain hadn’t fallen. And that this was due to direct leaf to leaf transfer.

Visually it was easy to appreciate that active, sporulating SLB infections located towards the tip of leaf three, which were at a similar height in the canopy to leaf two and the emerging flag leaf. And that all that is required for direct SLB transfer from leaf three to the upper leaves to readily occur is wind and leaf moisture.

This is illustrated in this photograph. Clearly visible are many active SLB lesions on leaf three which are at a similar height to emerging, or newly emerged, flag leaves. The perfect situation for direct leaf-to-leaf transfer of SLB.

Prosaro, the dual DMI fungicide from Bayer Crop Science, is a very effective fungicide that will control SLB, stripe rust and leaf rust in your crops.

To get the best from Prosaro apply to your crops when final leaf three is between ¾ emerged to fully emerged. Doing this ensures a protective coating of Prosaro is applied to the leaf prior to disease infection. The aim being to prevent disease infection, rather than trying to control established disease.

To ensure that a sound anti-resistance strategy is followed ensure you apply Prosaro in mixture with another fungicide active against SLB.

Finally, and very importantly, do not allow the interval between applying your GS32 fungicide and your GS39 fungicide (GS39 / T2 fungicide) to exceed 28 days.