Diplodia ear and stalk rot

Diplodia ear rot , stalk rot seed rot and seedling blight


The causal organism of this disease is the fungus Diplodia maydis (Berk.) Sacc. Other species of Diplodia also cause ear and stalk rot in warm wet climates (D. frumenti) and leaf spot (D. macrospora). Corn (maize) is the only host of the fungus in North America. Bamboo is the only other known host. The fungus overwinters on stalk debris as conidia contained in pycnidia and as mycelium or spores on seed. Spores are released during periods of wet weather and are splashed or windborne to host tissue. Plants are generally infected several weeks after silking. Roots, crowns, internodes and ears all server as infection sites. Infection is favored by dry weather prior to silking and 2-3 weeks of wet weather after silking. Other factors that influence infection and disease development include: physical characteristics of the hybrid, fertility levels, high plant populations, insect injury and foliar diseases.

Symptoms


Ear rot infections tend to be more severe on hybrids with upright ears and loose husks or insect injury. The former physical feature allows water to collect in ears creating an ideal microclimate for infection and disease development. Loose husks and insect injury leave kernels exposed to higher levels of inoculum than would be experienced if kernels were covered. Symptoms also vary depending on the time of infection. Plants exposed to an early infection ( 2-3 weeks after silking) have bleached husks and rotted ears. Infection most often occurs from the base end up and large amount of mycelium grow around the ear and between the husks. Extensive mycelial growth causes ears to remain erect and husks to bind tightly to the ear. As the season progresses, pycnidia form on the husks and kernels. Rotted seed exhibits poor germination or may germinate prematurely ( a condition called vivipary). Ears infected later in the season often exhibit no outward symptoms. Mycelial growth is limited to white growth between the kernels and on the cob. The tips of the kernels are discolored and may contain pycnidia. Seedlings grown from infected seed commonly succumb to seedling blight.

Stalk rot infection most often occurs at the crown, however, root and internode infections often occur. Infected plants often wilt suddenly and the leaves become grayish green. Internodes on the lower stalk are discolored and pith tissue disintegrates and turns brown. The vascular bundles remain in tact and stalks feel spongy. Infection generally progresses up the stalk and into the root, but infection of ears via a stalk rot infection is rare. Lodging is also a common symptom associated with this disease. Subepidermal pycnidia form at the nodes late in the season.

Plant Health Management

References

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Caveat

This description is presented for information only and no endorsement is intended for products listed, nor criticism meant for products not mentioned. Always consult the product label before purchasing and using any pesticide.

Material contained on the Links from the page are the responsibility of the linked page's author(s).

This page was drafted by: Jane Christensen, Department of Plant Pathology, University of Nebraska-Lincoln

Disease images were provided by: Dr. David Wysong, Department of Plant Pathology, University of Nebraska-Lincoln

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This page is authored and maintained by:
Dr. J.E. Partridge, Department of Plant Pathology, University of Nebraska-Lincoln

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Copyright (C) 2003 J.E. Partridge, University of Nebraska-Lincoln. All Rights Reserved.