Sweet corn ears are generally ready for harvest approximately three weeks after the first silk emergency, depending on the temperature. Silk will start to turn brown about two weeks after emergence. Ears should be harvested when the kernels appear to be milky when
punctured with a thumbnail. It is called the milky stage. The un- husked ears should feel firm, have full kernel to the top of the ear and have brown dry silk.
Fully ripe kernels of super sweet varieties will still posses a clear, watery juice.
Harvesting method and field assembly.
Ears of standard varieties will remain in prime condition for only a short time in warm weather when compared to cool weather. Harvest in the early morning when both the ears and the weather are cool. High temperature will quickly lower the eating quality of sweet corn. When
harvesting, break the stem of the ear as close to the ear as possible without breaking the main stalk. Long shanks and flag leaves should be clipped to reduce moisture losses. Ideally, ears should be cooled to 0˚C within an hour of harvesting. Use field plastic or wooden crates to handle the corn.
If corn cannot be refrigerated immediately, it should be stored in the shade to reduce heating from the sun. When harvesting for direct market supply, harvest only a one-day supply and keep as cool as possible. Ears can be packed in field crates topped with ice, and kept at 0o C. Ears, in these conditions will be marketable for 5 to 10 days.
Traditional sweet corn varieties are seldom stored for more than a few days, because of the resulting serious deterioration and loss of tenderness and sweetness. The loss of sugar (which is converted to starch) fastens with the increase of temperature. Prompt cooling at 0o C and high Relative Humidity will extend shelf-life.