Corn Pests & Disease Symptoms

Corn grows quickly and can provide you with a bounty of sweet ears, perfect for raw or cooked consumption, but humans are not the only ones that likes corn. Various fungal and bacterial diseases, as well as insect pests, also have a penchant for corn. Symptoms vary depending on the specific disease or insect. Knowing the symptoms can help you identify the underlying problem.

Grass Thrips

Grass thrips are very common among corn starting in late April, according to the University of Missouri. These insects don't just feed on the corn plant, but they can also carry various fungal diseases. The insects are approximately 1/16 inch long and yellow in color. They're commonly found on the underside of the leaves on the lower portion of the plant. The leaves turn silver after a heavy infestation.

Corn Leafminer

Corn leafminers are the worm larvae of a fly that lays its eggs on the corn plant's leaves. When the eggs hatch, the larvae begin feeding and leave behind transparent tunnels in the foliage. Such symptoms appear from the bottom row of leaves up to the sixth leaf on the plant, according to the University of California.


Armyworms cause notched edges on the corn plant's foliage as they feed. When the worms attack seedlings, they will often strip the entire plant of its leaves, sometimes overnight, according to the University of Missouri. The worms themselves can be identified by their small size--the worms measure approximately 1 1/2 inches--and green, hairless skin.

Maize Dwarf Mosaic

The viral maize dwarf mosaic disease makes itself evident on the surface of the corn plant's foliage. The leaves take on a streaky appearance, alternating between green and yellow streaks, according to the University of California. As the infection progresses and the corn plant grows, the entire leaf can take on a yellow appearance. Side effects include poor corn ear production and stunted plant growth.

Pythium Stalk Rot

The Pythium aphanidermatum pathogen is the cause of stalk rot, according to the University of Illinois. The base of the plant may take on a water-soaked appearance, but this is usually not noticed until the entire stalk falls over because the rest of the plant retains its green appearance. The disease usually occurs during warm, wet-weather periods and attacks mature corn plants around the time of pollination.

Keywords: corn pest symptoms, corn disease symptoms, corn problems

About this Author

Josh Duvauchelle is an editor and journalist with more than 10 years' experience. His work has appeared in various magazines, including "Honolulu Magazine," which has more paid subscribers than any other magazine in Hawaii. He graduated with honors from Trinity Western University, holding a Bachelor of Arts in professional communications, and earned a certificate in applied leadership and public affairs from the Laurentian Leadership Centre.