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The P&PDL Picture of the Week
for 20 January 2003



Moldy Corn Stalks

Karen Rane, Plant Disease Diagnostician, Botany & Plant Pathology, Purdue University

These corn stalks were submitted last week to the Plant and Pest Diagnostic Laboratory. Yields from this field were unexpectedly low last fall at harvest. The client wanted to know the identity of the fuzzy dark mold on the corn stalk residue, and assumed the fungus had played a role in the yield loss.

The dark fungal growth on this sample is NOT indicative of a plant disease. Many species of fungi will grow on dead and decaying plant material. They are called saprophytic fungi, or saprophytes, and they are essential for the decomposition of plant residues into organic matter found in soil. Without saprophytic microorganisms, the surface of the earth would be covered in the “ remains” of all living things! Many saprophytic fungi produce colored spores and/or mycelium, which can give the colonized plant tissue a distinctive color or cause the surface of the plant material to be powdery or fuzzy in texture.

Fungi growing on dead plant tissue invade too late to have any effect on yield. At this point in time, months after harvest, it is very difficult if not impossible to confirm the cause of poor yield by examining a stalk sample. Careful evaluation of detailed crop history information, including environmental conditions, pesticides applied, and other cultural practices used, may reveal potential factors that could have contributed to reduced yield.

Click on the small image to view a larger image.

Corn stalks colonized by secondary, saprophytic fungi. The dark fungal growth is powdery, and rubs off when touched.
Closeup of stalk tissue colonized by saprophytic fungi.

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Last updated: 21 January 2003/amd
The Plant & Pest Diagnostic Laboratory at Purdue University