All About Sweet Corn

Sweet corn fresh from the garden or farmers market makes a tasty addition to a summer picnic. Iowa State University Extension and Outreach horticulturists offer tips for harvesting and storing sweet corn, and examine some of the pollination and disease issues that can impact yield. For more information, contact the ISU Hortline at 515-294-3108 or hortline@iastate.edu.

When should I harvest sweet corn?
Harvest sweet corn 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 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 15 to 23 days. Sweet corn matures faster in hot weather and slower in cool weather.

Many sweet corn cultivars produce two ears per plant. The lower ear usually matures one or two days ahead of the upper one. To harvest the ears, hold the stalk below the ear. Twist the tip of the ear toward the ground until it breaks off.

How should sweet corn be stored?
Store unhusked sweet corn in the refrigerator immediately after harvest. Standard sweet corn cultivars may lose 50 percent of their sugar within 12 hours of harvest if not immediately refrigerated. Unhusked sweet corn can be stored in the refrigerator for four to eight days. New high sugar cultivars are slower to convert sugar to starch and have a longer storage life.

Why are the ears on my sweet corn poorly filled?
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. In gardens, plant sweet corn in blocks of four or more short rows to promote pollination.

What are the silvery white growths on some 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 cultivars 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 and destroyed before the galls break open.

Source: Iowa State University