White-tailed deer (Odocoileus virginianus) are among the common mammal pests of field corn in Indiana. The sight of deer grazing in harvested fields for dropped ears of corn is quite common in the fall, but these animals are also attracted to corn fields at other times of the year and can leave permanently damaged plants in their wake.
Early in the growing season, deer will sometimes feed on the whorls or tops of young plants from about growth stage V10 (ten leaves with visible leaf collars) to about V16 when the immature tassel, still inside the whorl, is 4 to 6 inches long.
Rather than actually eat the whorl leaves, the deer are apparently attracted to the succulent immature tassel. The results are decapitated plants whose young whorl leaves have simply been pulled out and (I can only imagine) the tassel somehow teased out and eaten.
The mostly intact, though no longer attached, whorl leaves are left behind on the ground along with the tell-tale evidence of hoof prints and deer scat. The decapitated plants usually survive and ear development will continue through pollination and on to maturity, though the ears are usually less than full size owing to the fact that most of the photosynthetic leaf area above the ears is missing.
These animals are also attracted to corn fields at about the time kernels reach milk stage of development (R3), often referred to as the “roasting ear” stage, in early to mid-August.
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The common symptoms resulting from deer feeding on corn at this stage of development are decapitated ears. The ear symptoms are sometimes mistaken for bird damage, but differ because of the distinct appearance of “cut” husks and missing ends of cobs resulting from the deer “chomping” off the ends of the ears.
Bird damage (crows, blackbirds, etc) more typically results in shredded ends of husks and barren cob tips.
Fortunately, deer damage to corn is often limited to the outer rows around the field edges. However, small fields of corn completely surrounded by woodlots or forest areas can sustain significant damage throughout the entire field by deer grazing in mid-August.
Deer damage to plants or ears of corn during the grain filling period often results in disease infection of the damaged plant tissue by common smut (Ustilago maydis) spores. This disease eventually develops into the ugly or beautiful (eyes of the beholder) mass of fungal tissue on damaged plant parts.