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Corn smut

Ustilago maydis

Profile

Corn blight is a fungal disease that mainly affects corn. Infestation is recognizable by conspicuous growths, so-called blight, on the above-ground parts of the plant. In Mexican cuisine, the infested corn kernels are a specialty (cuitlacoche - corn truffles).

Biology

The causal agent of corn blight, Ustilago maydis, belongs to the fungal family Ustilaginaceae and is an obligate parasite. This means that it can survive during the growth phase only in association with a living host. After infection, the growth of the blight is linked to the growth of the host tissue, which means good growing conditions for the corn also means good growing conditions for the blight. Only when the corn tissue has fully matured can new blight not develop.

Damage symptoms

This disease is a very conspicuous phenomenon due to the formation of the typical burnt bumps. The growths can develop on all above-ground organs of the corn plant and are initially covered with a silvery shiny tissue skin. Inside these bumps at this stage is already a black, slimy spore mass. In the course of further growth, this skin ruptures and the now powdery spore contents of the fungus are carried by rain and wind into the soil or onto other corn tissue.

Kleine, helle Beulen an einem Maisblatt
Maisbeulenbrand Beginn
Fortgeschrittene, helle Brandbeulen am Stiel und den Blättern einer Maispflanze
Maisbeulenbrand fortgeschritten
Weiße Brandbeulen mit dunklen aufgerissenen Stellen an einem Maiskolben
Maisbeulenbrand abreifend

Host plants

Host plants of corn bunt include only maize and the related maize origin species (teosinte), which are primarily native to South and Central America.

Distribution

Corn boll blight occurs worldwide in all warm, moderately dry climates. The occurrence is completely associated with the cultivation of maize due to high specialization.

Propagation and transmission

Infection usually occurs from permanent spores (teleutospores), in the form of which the fungus overwinters in the soil. In this form, the fungus can survive in the soil for several years (up to 10 years). Transmission of the spores by seed is also possible, but has little significance because of the standard seed dressing. In spring, the permanent spores germinate in the uppermost soil layer and form infection spores (basidiospores), which reach the corn plants by means of wind or rain splash. The spores germinate on young plant tissue and the typical gall tissue is formed. Injuries caused by hail, frit flies, storms or other factors such as late frosts or herbicide applications promote the invasion of the fungus.

Verbreitung der Sporen durch Wind und Regen. Infektion durch zwei kompatible Sporen, die Infektionssporen bilden und in die Pflanze eindringen. Der Pilz besiedelt die Pflanze und verursacht unkontrolliertes Zellwachstum. In den Gallen werden Sporen produziert. Sporen überdauern im Boden und starten einen neuen Infektionszyklus in der nächsten Wachstumsperiode.
Verbreitung und Lebenszyklus des Maisbeulenbrandes

Economic importance

Corn boll blight occurs annually, but it is very rarely of economic importance.

Prevention and control

Control with fungicides is not possible and also not economical

The spores adhering to the grain can be killed by dressing

Cultivation of less susceptible varieties

Control of the frit fly (see list of plant protection products approved in Austria)

Avoiding injuries during maintenance work

Services

Plant Health Services

Last updated: 08.04.2022

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