Septoria in wheat: symptoms, lifecycle and risk

21 May 2021

Septoria Tritici, or Septoria leaf blotch, is a devastating disease. By reducing green leaf area for photosynthesis, Septoria can cause losses of up to 50% in affected wheat crops and reductions in grain quality.

Disease risk to crops is high throughout most of the UK. The pathogen thrives in wet, windy conditions with temperatures between 15-25°C, which is why the wetter South and West are most severely impacted. To control Septoria, the combined use of fungicides and varietal resistance are used.

This creates other challenges for growers. Particularly as the environmental impact of fungicides is receiving greater attention, more effective treatments are being banned. Additionally, even the more resistant varieties are not completely immune to the disease; rapid Septoria detection test SwiftDetect has identified Septoria in such varieties, before it is even visible on the surface of the leaf.

Through a greater understanding of the disease, growers can better plan and react should their crops become infected with Septoria. Let’s go into more detail about what Septoria looks like when visible on the leaf, and its lifecycle.

Septoria leaf blotch symptoms

Part of the challenge with Septoria is that the disease has a long latent period of around 28 days. During this phase, leaves may appear to be green and healthy, as the fungus grows between its cells. Once visible lesions appear, controlling and treating the disease is more of a challenge.

We have previously mentioned the rapid Septoria detection test, SwiftDetect. This new test, using a process called qPCR, is so sensitive that it can identify Septoria in wheat during the latent period. In turn, growers are provided with an early warning, as well as insight into the level of disease in their crop so more informed decisions can be made. Find out more about the test here.

Once Septoria does emerge from the latent period, it often results in elongated, oval shaped lesions. These lesions often have a rectangular appearance as they are restricted by leaf veins. Leaf yellowing may occur around water-soaked patches, and lesions may merge forming areas of brown tissue. Pycnidia may emerge from mature lesions as small, black dots.

Septoria tritici symptoms in wheat

Symptoms often develop early in the crop life cycle. On young autumn wheat, the lowest leaves may develop symptoms as early as December. In the winter through to early spring, these lower leaves may die back as new leaves appear healthy. Let’s go into more detail on the life cycle of Septoria.

Septoria lifecycle

Over winter months, Septoria survives as dormant mycelium, pseudothecia and pycnidia. Pseudothecia release ascospores from previous wheat stubbles, which are spread by the wind. This initiates epidemics in the winter and early spring. Pycnidia release pycnidiospores, which usually spread spring and summer epidemics by rain splash from infected lower leaves. However, they can also travel without rain splash, when leaves 3 and 4 overlap upper leaves.

A lesion can form from a single spore. Once a spore lands on a new leaf, it takes around 12 hours to germinate. Providing conditions are damp, infection can take place within 24 hours of the spore landing. The latent period then begins, lasting between 14-28 days. At this stage, temperature can impact the length of the latent period; the closer conditions are to 15–20°C, the shorter the latent period. When conditions allow, the infection leaves the latent period and takes hold as lesions begin to appear.

Understanding risk

Although Septoria is widespread throughout the UK, there are numerous risk factors – some of which can be controlled to reduce risk.

Early drilling

By avoiding early drilling, disease risk can be significantly reduced. Crops sown early (September) can quickly be infected by Septoria, which then has more time to develop in the favourable autumn conditions. Particularly for susceptible varieties, drilling date plays an important role in high-pressure years. Drilling in October is therefore advised.

Varieties

The AHDB Recommended List scores winter wheat varieties based on their level of Septoria resistance. Although resistant crops are not immune to the disease and still need to be sprayed, infections are likely to be less severe if they do take. Therefore, resistant varieties can play an important part in your Septoria Strategy.

Weather

Although weather cannot be controlled, it can be monitored. Wet weather, particularly during May and June, leads to increased risk. Windy weather can increase the physical spread of spores; therefore, dry, easterly regions are at less risk. Finally, mild winters shorten latent periods, allowing infections to take hold faster.

Summary

  • Septoria thrives in wet, windy conditions between 15-25°C
  • The disease is widespread throughout the UK, though worst in the South and West
  • SwiftDetect is a rapid detection test, able to identify even low levels of Septoria. This can help growers make informed decisions with Septoria management
  • Septoria appears as yellow/ brown lesions on the leaf, after a latent period of around 20 days
  • There are ways to minimise risk of infection, by avoiding early drilling, selecting resistant varieties and monitoring weather

SwiftDetect for Septoria