Septoria nodorum disease symptoms in cereals

Causing a variety of symptoms in wheat, barley and rye, Parastagonospora nodorum has several common names – septoria nodorum, septoria seedling blight, leaf blotch and glume blotch. This page describes the pathogen, including its life cycle.

• Average annual losses in the UK probably do not exceed 3%, although yield losses up to 50% have been reported in trials
• Risk is greater in wet seasons, especially in the south-west of England
• The pathogen mainly infects wheat*, but occasionally infects barley and rye

*An advisory treatment threshold has been set for wheat. If over 10% of seed is infected (determined by a laboratory test), consider treatment.

P. nodorum can be seedborne and infect seedlings in cool, wet soils. The most common effect is poor plant establishment. It can also result in water-soaked, dark green areas on the coleoptile, which later become necrotic. Twisted, distorted and stunted seedlings may also occur. Symptoms are similar to those of microdochium seedling blight, although usually less severe. Laboratory analysis is often required to distinguish the causal organism.

On mature leaves, the first symptoms of P. nodorum infection are small necrotic lesions. Later, these develop into brown oval lesions, surrounded by a chlorotic halo. These lesions frequently coalesce to produce large areas of dead, dry and sometimes split tissue. Under high disease pressure, leaf symptoms can include small purplish-brown spots.

The indistinct pale brown pycnidia of P. nodorum may only be visible with a hand lens when lesions are held up to the light. They are often sunken within the lesions. Note: Septoria tritici blotch (caused by Zymoseptoria tritici) is associated with black pycnidia.

P. nodorum can also infect the ears, particularly of wheat, causing glume blotch. Dark brown patch-like burn marks develop on the glumes, which later become purple/brown. Glume blotch symptoms are easiest to see on green ears.

P. nodorum survives as dormant mycelium, and as pycnidia and pseudothecia on seed, stubble, crop debris, wild grasses, autumn-sown crops and volunteers. Infection of newly emerged crops occurs from these sources or from windborne ascospores released from infected stubble. Infection can also be seedborne. It is likely that the seedborne phase is responsible for septoria seedling blight.

As temperatures rise and humidity increases, pycnidiospores are produced from the pycnidia. These are splash-dispersed up the plant and from plant to plant. Temperatures of 20–27°C, together with long periods (6–16 hours) of high humidity, are optimal for spore production and germination. A period of rain is essential for spore dispersal. The disease cycle can be completed in 10–14 days during such conditions.

Spores produced from pseudothecia and pycnidia, which develop on the flag leaf and ear at the end of the season, can initiate infection in very early autumn-sown crops and volunteers, but infections on debris are more likely to initiate infection on new crops. Glume blotch infection of the ear can lead to infection of the seed.

Leaf blotch lesions on wheat leaves.

Glume blotch symptoms on a wheat ear.