Septoria tritici is the most important and damaging foliar disease on winter wheat crops grown in the UK and Ireland.
The pathogen acts to reduce green leaf area for photosynthesis.
It causes significant yield loss every year. It also affects grain quality. Losses of 50% may occur in severely affected crops.
Unusually dry weather throughout May and June may reduce losses, but heavy dews can still allow infection. Higher rainfall areas are most at risk of the disease gaining a foothold.
Septoria
Although wheat is the main host, the disease occasionally affects rye, triticale and some grass species.
Septoria often results in elongated, oval septoria lesions that are restricted by leaf veins, giving a rectangular appearance. Water-soaked patches often form, surrounded by leaf yellowing or death.
Lesions may coalesce to form large areas of necrotic brown tissue. Mature lesions contain characteristic, small (but visible) black fruiting bodies (pycnidia).
However, pycnidia are not always visible in immature lesions.
In most years, symptoms develop very early. On young autumn-sown wheat, symptoms may be evident by early December, and throughout the winter on the lowest leaves.
During leaf production phases of growth in the winter and early spring, it is common for new leaves to appear green and healthy, and for lower leaves to die back with typical symptoms. Stressed crops can show greater levels of infection.
Management
Varietal resistance is key to the management of septoria tritici.
Early drilled crops are exposed to incoming ascospores for longer periods and, hence, tend to have higher levels of disease throughout the winter and early spring.
Although the final level of disease is determined largely by weather conditions during stem extension, delaying drilling from mid-September to mid-October can reduce final disease pressure, irrespective of the variety.
According to the Agriculture and Horticulture Development Board (AHDB), fungicides are required for effective septoria tritici control in most crops.
However, to reduce reliance on fungicides and the risk of fungicide resistance developing, all other cultural control methods should first be adopted to reduce the level of input required.
A typical programme for control of the disease starts at T1 to limit the disease on the lower leaves. However, the T2 timing is the most important to keep upper leaves free of disease and so optimise yield and quality.
If the fungus is well into its latent phase, no fungicide will provide effective eradicant activity.
Again, according to AHDB, there is very rarely a yield benefit associated with controlling septoria at the T0 timing, even in the highest disease pressure situations.
However using septoria tritici active products at the T0 timing will reduce disease levels on the lower leaves, reducing the risk where T1 is delayed.
