Your guide to Septoria tritici blotch (STB)

This season we have seen considerable pressure of septoria tritici, therefore it is worthwhile to recap the biggest yield-robbing disease to winter wheat and what we can help do to fight against it. 

Septoria tritici blotch is a fungal disease of wheat that causes significant yield losses. It is caused by the fungus Zymoseptoria tritici, which overwinters on infected crop debris and plant residues. The fungus can infect wheat at any growth stage, but it is most common in the autumn and spring when the weather is cool and wet.

Symptoms of septoria tritici blotch of wheat typically appear on the lower leaves of wheat plants as small, brown spots. These spots enlarge and merge to form larger lesions. Rainfall splashes the spores up the leaves of the plant. As it does this the disease becomes more and more damaging to yield. Particularly bad cases of septoria tritici can reduce wheat yields by up to 50% and affect the milling and baking performance of the grain.

The last two springs we saw were less than favourable conditions for septoria tritici 2021 and 2022 saw both very dry warm springs which weren’t particularly favourable for the disease to spread so it kept the pressure lower. However, as previously mentioned this spring has been different, off the back of another overall mild winter which kept the spores alive. We have seen a cooler, windier and despite the lack of rainfall of late a wetter spring earlier on which has spread the spores not only across the country but up the plant canopy causing more yield damage.

Genetic resistance to diseases including septoria tritici is vitally important and the first step in tackling the disease. Giving your crop the best chance from the outset allows flexibility within the fungicide programme and timings.

Varieties which are tested by the AHDB RL programme are rated against septoria tritici from a 1-9, along with Wynnstay’s own observations we recommend looking for a rating of 6 above. Varieties which particularly stand out for their septoria resistance are KWS Extase, DSV’s Champion and LG Typhoon.

Varieties drilled earlier are exposed to the spores released from plant debris for longer so tend to show higher levels of septoria tritici. Delaying drilling from mid-September to mid-October reduces final disease pressure irrespective of variety – this is especially important if you choose a variety with a weaker septoria rating.

In the spring fungicides can be used to control septoria tritici blotch. Fungicide choice and application should be considered on a case-by-case basis however azoles and SHDI do provide good levels of control within most crops. T2 is the key timing for septoria tritici control and with T1 also usually containing chemistry to help with control.