The red ear of corn mentioned Chapter 13 signifies a colonial tradition. As described in Chapter 13, just like they had barn raisings and house raisings in which they turned difficult labor into a community event and celebration to help complete the work faster, the colonials also held cornhusking bees in which they made a festivity out of husking the year's corn harvest to have it ready in time to be stored for the winter. As Judith describes to Kit, the cornhusking bee was like a great big party full of music, "cakes and apples and cider." What's more, red ears of corn, which are a different breed of corn and rarer than yellow corn, were treated as a type of prize. Due to the red color, the colonials attributed romantic symbolism to the corn, much like we see the color red symbolizing love and romance today. Hence, the colonials used finding a red ear of corn as a courtship ritual, and those who found red corn were permitted to the publicly kiss the person of his/her choice, an activity that would normally be scorned by the Puritans ("Oh Shucks!," "Activities," p. 5.).
While one has to read between the lines a bit, the prize one wins by finding a red ear of corn is explained in the final passage of Chapter 13 in which Judith husks a red ear of corn. Since she has just become engaged to marry John Holbrook, she feels she has no need for a courtship ritual and throws the ear of corn to William who is still pursuing Kit to be his wife, as we see in the lines:
"I haven't any need for a thing like that! ... What am I offered for it?" Without waiting for an answer, she tossed it straight across the [husking] circle into William's hands. There were a few quick giggles, a hush of curiosity. Kit sat helpless, her cheeks on one, and then the laughter and the cheering left her giddy as William stepped resolutely forward to claim his forfeit.
Here, the word "forfeit" means fine, or fee. William was given/has won the red ear of corn; therefore, he is owed a fine or a prize, and the fine he takes is a kiss from Kit. Hence, we see that a red ear of corn was significant in colonial days as a courtship ritual.