Ear husks exhibit varying degrees of purple pigmentation from a trace to complete purpling.
Purple husks are not uncommon at harvest especially when stress conditions reduce ear size. Several factors can cause purpling of corn plant tissues late in the season. Husk purpling has been attributed to excess sugars accumulating in plant tissue that triggers formation of the red pigment anthocyanin. At harvest, the purpling is often most pronounced in plants from which ears have been reduced in size or ears with markedly reduced kernel numbers per ear due to some environmental stress. When corn borers burrow in stalks and ear shanks they can disrupt and prevent the normal redistribution of sugars from the stalk into the developing kernels. Purpling is also associated with plants producing blunt earss. In stunted ears the limited numbers of kernels may not use all the sugars being produced by the plants, so sugars accumulate and plants turn purple. Traces of purpling on plants, which appear healthy, with normal ears, also occur and this has been related to plants producing more sugars than the ear can assimilate due to very favorable growing conditions. The extent to which plants turn purple is also influenced by hybrid genetics with some hybrids more inclined to exhibit purpling than others when some stress disrupts the flow of sugar from leaves and stalks during grain fill.
Husk purpling may be indicative of stress conditions or injury.