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Common Smut

CROPS IMPACTED: Corn

Common Smut

Family: Ustilaginaceae

Common Smut Common Smut

About Common Smut

Life Cycle

Common smut starts out as small white masses on the host plant; this usually happens about 9 days after infection. These masses, called galls, are firm and covered with a semigloss outer layer of tissue. 48 hours after initial formation, the galls will grow larger in size. As these galls continue to age, about 14 to 15 days following infection the tissue inside will become fleshy and begins to appear streaked gray or black as the teliospores form. Approximately 22 days following infection the spores turn powdery, the outer layer of the gall will break and the sooty teliospores will be released into the air. If they are well-hydrated, the spores will be less sooty and release as more of a wet mess. This fungus overwinters in soil and plant debris; under the right conditions spores have the ability to last for years after they were released from the gall.

Common Smut Identification and Habitat

Identification

Common smut of corn can be recognized easily from the galls that are formed by the fungus. These masses are filled with dark teliospores. While common smut is typically seen as a nuisance to farmers throughout many parts of the world, in Mexico it is actually eaten and considered a delicacy called huitlacoche. These galls have a large size range with a diameter starting at under a centimeter and can reach more than 30 centimeters. Any of the plants cells that are dividable can be vulnerable to infection from this disease; however, these sooty spore filled masses are more common on ears, stalks, and tassels. Infection is also possible but unlikely to occur on the plant below ground if the shoot was affected when the plant was young. After approximately 10 to 14 days of being infected, masses will be easily spotted. However, if the ear is infected, this disease can be noticed about 5 days after initial infection by way of marred or discolored kernels. The size of the mass will depend on present conditions of the plant and at what time the infection occurred. If the gall forms on leaves, it tends to be significantly smaller than other infection areas; the galls on the leaves will usually just harden and dry. Stalk galls average a diameter of about 25 centimeters. When the ears are infected, typically just the top kernels are affected; however, sometimes galls can form across all of the kernels when the infection is bad.

Habitat

Common smut is typically found on farms that grow corn as a crop, or in gardens. This disease is caused by the fungus Ustilago zeae. When the galls rupture and release the thousands of spores that it held, these spores will travel in the wind or rain to new host plants. Common corn smut prefers weather that is humid and wet. When a corn plant is injured from things such as heavy rain fall or cultivation, it presents as a perfect opportunity for this fungus to infect the plant.

Common Smut Management and Control Methods

Cultural Control

There are some corn varieties and hybrids available that are resistant to this fungus. Also, avoid more susceptible corn types such as flint corn. If the infection takes place in a small garden, it is suggested to collect and destroy the masses before the spores are released. This will limit the spread of this disease to other plants. Avoid plant injury to make it more challenging for this fungus to enter a plant. This includes controlling pests that eat into crops such as corn borers. Plan to remove all plant debris from the garden or field, which also helps reduce spread. As well, never compost the plant parts.

Chemical Control

When cultural control methods are not enough to manage common smut, plan to use fungicides such as copper or sulfur applications as soon as possible. This can be continued each week when the conditions for the fungus are advantageous. That being said, always carefully read the label for cautions and proper application before use.

Alternative Common Smut Names

  • • Corn smut
  • • Boil smut
  • • Blister smut

Sources

http://www.apsnet.org/edcenter/intropp/lessons/fungi/Basidiomycetes/Pages/CornSmut.aspx

http://ohioline.osu.edu/hyg-fact/3000/3119.html