An Overview of Stagonospora Nodorum Leaf and Glume Blotch

Symptoms and Signs

The fungus that causes SNB can infect wheat throughout the growing season. Signs and symptoms of the disease are visible on both leaves and glumes. 

On foliage, symptoms generally begin with small yellow flecks or spots. These spots then develop into lens-shaped lesions that are surrounded by yellow halos, which may become brown or grayish brown (Figure 1). The lesions may further coalesce to produce large areas of dead, brown tissue. 

During periods of high humidity, fungal fruiting bodies called pycnidia (small round structures) develop in the lesions. The pycnidia are generally brown to orange and are difficult to distinguish within the brown lesions.

Stem infections also occur and may be most pronounced near nodes. On wheat heads, the fungus causes glume blotch symptoms (Figure 2). Glume infections develop as purple-brown or grayish brown streaks and blotches. These symptoms often start at the tips of glumes, and then eventually spread throughout the whole spike simultaneously. Pycnidia will develop in symptomatic tissue. 

The fungus can infect seeds, which reduces test weights. Seedlings that emerge from infected seed may die soon after emergence or develop dark coleoptile lesions.

Development and Disease Cycle

The main ways this fungus overwinters are in fungal growths (called mycelia) in wheat residue and fungal fruiting bodies. Seed can transmit the fungus (Figure 3). Other reservoirs of inoculum include volunteer wheat and wild grasses infected by P. nodorum. 

Initial infections arise from spores that were produced from fungal fruiting bodies and then dispersed by wind or splashing rain. Infection requires at least 12 hours of free moisture and temperatures between 59-77°F (15-25°C). After infection, symptoms are not observed for at least 10-14 days. Symptom development is favored by temperatures between 68-81°F (20-27 °C). New pycnidia develop in the lesions 10-20 days after infection. Glume blotch occurs when wet, humid conditions persist. 

Yield Losses and Impact

When conditions favor disease development, SNB can cause up to 50 percent yield loss and increase grain dockage due to poor test weight and reduced quality. Yield loss is attributed to leaf and glume infection, which reduces the area the plant can use to perform photosynthesis and fill grain.

The timing of infection and disease development influences the risk of yield loss. Infections that occur before heading generally result in greater yield losses. 

Diseases, Disorders, and Injury with Similar Symptoms 

Management

Successfully managing SNB requires integrating several management practices, including:

1. Plant certified disease-free seed to minimize the risk of seed-transmitted SNB.

2. Select wheat varieties with SNB resistance. Resistance to SNB on the leaves and glumes may differ, so check with seed companies to determine how they established their resistance ratings.  

3. Apply a foliar fungicide when SNB risk is high. When selecting a fungicide to manage SNB, consider the crop growth stage. Many fungicides are labeled to control SNB; however, you should not apply fungicides that contain a quinone outside inhibiting (QoI/Strobilurin, FRAC group 11) active ingredient after head emergence. QoI fungicides may increase mycotoxins produced by the Fusarium head blight fungus, which is also favored by the warm, wet conditions that promote SNB. 

4. Populations of S. nodorum resistant to QoI fungicides have recently been reported in the United States. To minimize the development of fungicide resistance, farmers should use fungicide products that contain active ingredients from multiple fungicide classes.

More information about products that may have efficacy against SNB are available in Fungicide Efficacy for Control of Wheat Diseases (CPN-3002).

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Acknowledgments

Authors

Nathan Kleczewski, University of Illinois; Navjot Kaur, Virginia Tech; Gary Bergstrom, Cornell University; Carl Bradley, University of Kentucky; Martin Chilvers, Michigan State University; Alyssa Collins, Pennsylvania State University; Christina Cowger, North Carolina State University; Erick DeWolf, Kansas State University; Andrew Friskop, North Dakota State University; Alyssa Koehler, University of Delaware; Hillary Mehl, Virginia Tech; Pierce Paul, Ohio State University; Jorge Salgado, Ohio State University; Adam Sisson, Iowa State University; Damon Smith, University of Wisconsin; Kiersten Wise, University of Kentucky; and Heather Young-Kelly, University of Tennessee

Reviewers 

Kaitlyn Bissonnette, University of Missouri; Emmanuel Byamukama, South Dakota State University; Alfredo Martinez Espinoza, University of Georgia; Travis Faske, University of Arkansas; Bob Hunger, Oklahoma State University; Juliet Marshall, University of Idaho; Lucky Mehra, Kansas State University; Daren Mueller, Iowa State University; Nidhi Rawat, University of Maryland; and Albert Tenuta, Ontario Ministry of Agriculture, Food and Rural Affairs

Photographers

All photos were provided by and are the property of the authors and reviewers.

Sponsors

This project was funded in part through Growing Forward 2 (GF2), a federal-provincial territorial initiative. The Agricultural Adaptation Council assists in the delivery of GF2 in Ontario. The authors thank the United States Department of Agriculture - National Institute of Food and Agriculture and the Grain Farmers of Ontario for their support.