Stagonospora leaf and glume blotch of wheat
Stagonospora leaf and glume blotch is very common in the U.S. and Canada and is often found with Septoria leaf spot. This disease is caused by Parastagonospora nodorum and P. avenae f. sp. triticae. The leaf blotch phase of this disease can lead to a head infection phase, called glume blotch. Seed may also be infected. When infected seed is planted, the coleoptile will develop long dark lesions in fall. Typically, symptoms of leaf blotch become evident in spring as small, yellow spots on lower leaves. Spots enlarge, becoming gray or brown, elliptical-shaped lesions. The lesions have a chlorotic margin and become necrotic in the center as time passes. Brown fruiting structures will develop in necrotic lesion centers, producing spores that can infect other leaves. Lesions may coalesce. Stems and tiller nodes can be infected. Infected glumes have a purple to brown discoloration and can appear dirty or slightly water-soaked from a distance. Fruiting structures are generally present in infected glume tissue. Symptoms can be observed from tillering stages through ripening, and on seed. Look for yellow lesion margins and brown fruiting structures (as opposed to black or no fruiting structures) within infected tissue to help differentiate from other diseases.
Moderate temperatures 68-75oF and wet, rainy weather favor Stagonospora leaf and glume blotch, as does high humidity within the plant canopy. The fungus survives in seed and residue, so planting infected seed or planting into infested residue encourages disease development. Yield reduction is greatest when damage to the flag leaf occurs prior to or around FGS 10.3, when heading is half complete.
Moderately resistant varieties are available. Plant disease free or fungicide treated seed. Encouraging residue decomposition, planting wheat in wider rows, avoiding over fertilization (especially nitrogen), and crop rotation can help to reduce disease. Fungicides are labeled for management of Stagonospora leaf and glume blotch. Scout and consider factors such as varietal susceptibility, forecasted weather, length of rotation away from wheat, and yield potential prior to fungicide application.
Gallery images: C. Grau.