NC State Extension Publications

Introduction

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Aerial web blight (syn. aerial blight or Rhizoctonia aerial blight) is not a common disease for soybeans in North Carolina, but may cause local losses where conditions are conducive for development. Diagnosis can be difficult in the field because fungal structures may not be present. Because it's not a common problem for NC soybeans, the impact of management options on yield is largely unknown.

Pathogen

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Rhizoctonia solani is the causal agent of aerial web blight. The fungus survives in the soil or previous crop debris as sclerotia (overwintering structures). As disease progresses, small, brown, irregularly shaped sclerotia (overwintering structures) may form inside of the web-like hyphae.

Host Range

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Rhizoctonia solani has a very wide host range, and rotational crops like peanut, cotton, tobacco, and other common vegetable rotations are susceptible.

Symptoms and Signs

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Initially foliage appears water-soaked, and gray-green. The foliage may become brown and necrotic where the fungus has colonized (Figure 1). Leaves stems, and pods may all be impacted. During warm, wet weather conditions, the fungus forms fungal mats over the surface of plants causing the webbed appearance. Small, irregularly-shaped, sclerotia (overwintering structures) may also be formed in the fungal mats starting out white and becoming dark brown (Figure 2).

Photo of necrotic foliar damage

Figure 1. Patchy distribution of necrotic foliage affected by web blight.

Photo courtesy of Tim Britton

Webbing

Figure 2. Fungal hyphae "webbing" observed on soybean leaves affected by web blight

Photo courtesy of Mike Carroll

Disease Cycle and Conditions Favorable for Disease

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The fungus survives in crop debris or soil as sclerotia. Under warm, wet conditions (high humidity and 77-90°F/25-32°C) the fungus grows from sclerotia to form fungal mats over the plant surface. Disease is more severe in dense plantings or fields surrounded by trees because they increase the humidity and decrease airflow within the field. After harvest, the sclerotia survive in remaining plant debris or in the soil until suitable conditions for growth are present.

Management

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There is no host resistance to aerial web blight, but some varieties may be less susceptible. Sorghum and corn are poor hosts, and rotations with those crops for two years may reduce incidence in future stands. If a susceptible crop is planted, and environmental conditions continue to be conducive to disease, a fungicide application may be beneficial. In field trials in Mississippi, fungicide applications containing a strobilurin protected yield when applied at R5.

Useful Resources

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The NCSU Plant Disease and Insect Clinic provides diagnostics and control recommendations

The Extension Plant Pathology portal provides information on crop disease management

The North Carolina Agricultural Chemicals Manual provides pesticide information for common diseases of North Carolina. The manual recommendations do not replace those described on the pesticide label, and the label must be followed.

Acknowledgements

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This factsheet was prepared by the NCSU Field Crops and Tobacco Pathology Lab in 2020.

Author

Assistant Professor & Extension Specialist
Entomology & Plant Pathology

Find more information at the following NC State Extension websites:

Publication date: Sept. 10, 2020

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N.C. Cooperative Extension prohibits discrimination and harassment regardless of age, color, disability, family and marital status, gender identity, national origin, political beliefs, race, religion, sex (including pregnancy), sexual orientation and veteran status.