Don’t Sweat the Small Stuff: Disregard those Purple to Black Spots Against the Corn Stalk at the Base of the Leaf Collar

Tom Allen, Extension Plant Pathologist
By Tom Allen, Extension Plant Pathologist June 4, 2012 11:23

Don’t Sweat the Small Stuff: Disregard those Purple to Black Spots Against the Corn Stalk at the Base of the Leaf Collar

Annually, about this time of year, I receive telephone calls regarding some of the more common maladies in corn that don’t result in a yield loss.  Corn is a large plant, with a tremendous amount of surface area.  Oftentimes a lesion will develop on the plant in response to an environmental situation.  One of the more common lesions to develop is in response to tassel pieces or pollen that falls in between the collar of the leaf and the stalk.  Typically, the lesions can be observed throughout the canopy of most corn fields, even in the most highly managed situations, and can readily be observed on most hybrids.  In fact, the specific disorder (I hesitate to refer to this as a “disease”), purple leaf sheath (or yeast spot), can be found in almost all corn fields to some degree or another and is simply due to a more conducive environment present at that particular location on the plant and saprophytic organisms taking advantage of the situation (e.g. yeasts).  Yeasts are one of the most common inhabitants on a plant’s leaf surface.  However, yeasts are generally nutritionally challenged and require specific nutrients to thrive.  The environment within the canopy and more specifically down in the leaf collar and against the stalk is a great collection point for moisture and low levels of nutrients.  In some cases, additional saprophytic fungi can gather and feed on what the yeasts don’t require.  However, at no time is any of this harmful to the corn plant.

I realize that in some cases yeast spots can look much worse than they really are.  The staining present underneath the leaf doesn’t penetrate the stalk.  Peel the leaf back and away from the stalk and if you have to, scrape off some of the outer layer of the stalk and typically the stained area won’t go much below the surface.

Purple leaf sheath is another one of those situations where a fungicide is NOT beneficial.  The fungi (yeast or otherwise saprophytic fungi) or bacteria involved in producing the stained area are secondary and should not be considered threatening towards producing high yielding corn.

Tassel pieces and pollen collect against the stalk down in the leaf collar and provide a conducive environment and food source for saprophytic organisms.

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Tom Allen, Extension Plant Pathologist
By Tom Allen, Extension Plant Pathologist June 4, 2012 11:23
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