Yard and Garden: Sweet Corn

AMES, Iowa – Sweet corn is one of the most popular vegetables in the home garden, roadside stands and farmers' markets. This summer’s hot, dry weather has growers asking Iowa State University Extension and Outreach horticulture specialists about sweet corn. To have additional questions answered, contact the experts at hortline@iastate.edu or call 515-294-3108.

The ears on my sweet corn are poorly filled. What are possible causes? 

Poorly filled ears are usually the result of poor pollination. Hot, dry winds and dry soil conditions may adversely affect pollination and fertilization and result in poorly filled ears. Water sweet corn during pollination if the soil is dry. Improper planting also may affect pollination. Corn is wind pollinated. Plant sweet corn in blocks of four or more short rows to promote pollination. 

When should I harvest sweet corn? 

Sweet corn should be harvested at the milk stage. At this stage, the silks are brown and dry at the ear tip. When punctured with a thumbnail, the soft kernels produce a milky juice. Over-mature sweet corn is tough and doughy. An immature ear will not be completely filled to the tip and the kernels produce a clear, watery liquid when punctured.  

The harvest date can be estimated by noting the date of silk emergence. The number of days from silk emergence to harvest is approximately 18 to 23 days. Prime maturity, however, may be reached in 15 days or less if day and night temperatures are exceptionally warm. Most hybrid sweet corn varieties produce two ears per plant. The upper ear usually matures one or two days before the lower ear.  

Harvest sweet corn by grasping the ear at its base and then twisting downward. Use or refrigerate sweet corn immediately after harvest. Optimum storage conditions for sweet corn are a temperature of 32 F and a relative humidity of 95 percent. 

What are silvery white growths on the tassels of my sweet corn? 

The silvery white growths are likely common corn smut. Common corn smut is a fungal disease. Smut galls can develop on the stalks, leaves, ears or tassels of sweet corn. When broken open or “ripe,” the galls release millions of powdery black spores. Spores released by the smut galls fall to the soil where they may survive for many years.  

Several factors affect the severity of common smut. Corn smut is usually more common on plants heavily fertilized with nitrogen and those damaged by hail or mechanical means. Hot, dry weather also increases the incidence of corn smut.  

Corn smut control strategies include avoiding varieties that are highly susceptible to smut, avoiding mechanical injury to plants during cultivation and providing adequate (but not excessive) amounts of nitrogen. Smut infested portions of the sweet corn plant (or the entire plant) should be removed from the garden before the galls break open and destroyed.  

In Mexico, corn smut galls (referred to as huitlacoche) are regarded as a delicacy and used in soups, casseroles and other dishes.