Stenocarpella stalk rot is caused by Stenocarpella species that also cause Stenocarpella (Diplodia) ear rot and Macrospora leaf stripe. Stenocarpella stalk rot is common in most maize growing regions globally and can cause considerable yield loss. Infection of the ears by Stenocarpella species can result in production of mycotoxins that are toxic to humans and livestock.

Pathogen

Stenocarpella maydis (syn. Diplodia maydis) – prevalent in cool, humid temperate regions.
Stenocarpella macrospora (syn. Diplodia macrospora) – prevalent in warm, humid regions.

Symptoms

Symptoms of Stenocarpella stalk rot generally become apparent after silking. It causes browning of the pith of the basal internodes of the maize plant. Oval, elongate lesions (up to 10cm long) with pale cream-brown centers and dark brown borders often form on infected stalk tissue. Leaves wilt suddenly and become grayish-green.

The pith in infected stalk tissue becomes discolored and weakened and the crop stand is characterized by lodging. Symptoms of Stenocarpella stalk rot are similar to those caused by Gibberella stalk rot, but can be distinguished by abundant pycnidia that form subepidermally in infected internodes late in the season.

Confirmation

Stenocarpella stalk rot can be distinguished from other stalk rots by the formation of abundant, dark-colored pycnidia on infected stalk internodes late in the season. For accurate confirmation of pathogen identity, microscopic analysis is recommended. Pycnidia of both S. maydis and S. macrospora are flask-shaped (spherical with circular protruding papillate ostiole) and multicellular. Pycnidia are 150-450µm in diameter while the ostiole is typically 30-40µm in diameter.

Pycnidia contain pale brown, straight to slightly curved conidia with rounded ends.  Conidia of S. macrospora are 0-3 septate, measuring 7-12 × 44-82µm. Conidia of S. maydis are 1-2 septate and measure 5-8 × 15-34µm.  Occasionally pycnidia contain colorless, narrow spores that measure 1-2 × 25-35µm. A sexual stage for these fungi has not been recorded.

Incidence and factors favoring disease severity

Stenocarpella stalk rot is favored by dry weather early in the growing season followed by frequent rainfall after silking. Strong winds, rainfall, and insects aid the dissemination of conidia. As the causal fungi overwinter in infected crop debris, Stenocarpella stalk rot is more prevalent in regions where reduced tillage is employed. As with other stalk rots, low potassium content in the soil encourages disease severity.

S. macrospora is more prevalent in warm, humid regions, while S. maydis is more prevalent in cool, humid and temperate regions. Conidia of S. maydis lose their viability at high temperatures or following exposure to sunlight.

Host range

Both S. maydis and S. macrospora infect maize as the primary host. However, S. maydis has also been reported to infect bamboo.

Life cycle

The causal fungi overwinter as pycnidia in infected maize stalk debris in or on the soil surface.  In response to warm and moist conditions, conidia are exuded from the conidia in long cirrhi and disseminated by wind and rain. It is also thought that insects play a role in the dispersal of conidia. Maize plants are typically infected through the crown, mesocotyl, roots, or occasionally through the nodes between the crown and ear. Stalks are then colonized, leading to stalk rot and formation of pycnidia on infected stalk tissue.

Damage

• Mechanism of damage: Infection of the stalk leads to disruptions in the translocation of water and nutrients, resulting in yield loss. Additionally, infection of the stalk predisposes plants to crop lodging, bringing about premature plant death and yield loss particularly where maize is machine harvested.
• When damage is important: Stenocarpella stalk rot is most severe once disease has spread to the second internode above the ground and 50% of the stalk tissue is infected. Maize plants can tolerate reduced levels of infection. Stenocarpella species can also be seed borne and in these cases can cause extensive seedling damage/death and loss of germination.
• Economic importance: Yield loss due to stalk rots can exceed 50% in conditions that favor disease severity. S. maydis has been shown to cause up to 37% loss of germination when infected seed is cultivated.

Global distribution

The global distribution of S. maydis and S. macrospora are shown in Figures 1 and 2 respectively.

Figure 1. Geographic distribution of S. maydis

Figure 2. Geographic distribution of S. macrospora

Management principles

Host resistance

• Cultivation of resistant varieties offers the most practical and cost-effective means of Stenocarpella stalk rot management.
• Varieties that are resistant to Gibberella stalk rot also tend to be resistant to Stenocarpella stalk rot.
• Flint varieties are generally more resistant than dent varieties.

Fungicides

• Once symptoms appear it is usually too late to control the disease by foliar application of fungicides.
• Seeds treated with fungicide are effective in controlling early infection of the seedlings.

Biological control

• Treatment of S. maydis infected seed with antagonistic Streptomyces species has been shown to effectively reduce disease severity. However, this technique remains at the experimental stage.

Cultural control

• Balanced soil fertility with adequate potassium will reduce incidence of Stenocarpella stalk rot.
• Management of infected stalks following crop harvest.
• Harvesting early will reduce losses due to lodging following crop maturity.
• Crop rotation is effective as both S. macrospora and S. maydis predominantly infect maize.
• Lower plant density results in reduced disease severity.

References

Brenna, W and J.E.F. Figueiredo. 2005. Biological control of Stenocarpella maydis in maize seed with antagonistic Streptomyces sp. isolates. Journal of Phytopathology 153: 623-6.

Casa, R.T., L. Zambolim and E.M. Reis. 1998. Transmission and control of Diplodia in maize seeds. Fitopatologia Brasileira 23: 436-41.

CIMMYT. 2004. Maize Diseases: A guide for Field Identification. 4th Edition. Mexico, D.F.: CIMMYT.

Michaelson, M.E. 1957. Factors affecting development of stalk rot of corn caused by Diplodia zeae and Gibberella zeae. Phytopathology 47: 499-503.

Ngiwe, C. 1974. Effect of Diplodia zeae and B-Phomopsis on the germination of seeds of maize (Zea mays). Plant Disease Reporter 58:414-15.

OEPP/EPPO. 2006. Data sheets on quarantine pests No.67: Stenocarpella macrospora and Stenocarpella maydis.  http://www.eppo.org/QUARANTINE/fungi/Stenocarpella_macrospora/DIPDSP_ds.pdf.

Olatinwo, R.O., K.F. Cardwell, M.L. Deadman and A.M. Julian. 1999. Epidemiology of Stenocarpella macrospore (Earle) Sutton on maize in the midaltitude zone of Nigeria. Journal of Phytopathology 146: 347‑52.

White, D.G. 1999. Charcoal Rot. In Donald G. White (ed), Compendium of Corn Diseases. St. Paul, Minnesota: The American Phytopathology Society. Pp. 40.

Contributor: Biswanath Das