Corn senescence (death of the plant) occurs naturally near the end of grain fill as plant metabolism slowly deteriorates. Leaf senescence in corn fields throughout Indiana has occurred rapidly during the last three to four weeks, sooner than most folks think is typical. A number of causes have been offered up in explanation of the rapid development of leaf "firing" this season including anthracnose top-dieback, gray leaf spot, stalk rots, nitrogen deficiency, and drought stress.
Additionally, the pattern of leaf senescence has been unusual in that the upper leaves have died as rapidly as the lower leaves, leaving green leaves only in the center part of the plants near the maturing ears. In the Midwest, this pattern of upper leaf senescence is typically blamed on anthracnose, European corn borer injury, or a combination of heat and drought stress. In many of the fields exhibiting this unusual pattern of leaf death, none of these causes can be identified as the main culprit.
Interestingly, the pattern of upper and lower leaf senescence may not be that unusual in a physiological sense. Research in Ontario, Canada in the late 1970's (Tollenaar & Daynard, 1978, Leaf Senescence in Short-Season Maize Hybrids, Can. J. Plant Sci. 58: 869-874) documented this same pattern of senescence among ten adapted dent corn hybrids. Furthermore, a faster rate of leaf senescence during one of the years of the study was attributed to a warmer, drier weather pattern during the grain fill period (not unlike much of Indiana in 1998) that accelerated the rate of grain filling.
All of the stresses mentioned above have likely contributed to the overall rapid shutdown of photosynthetic leaf area. The upper/lower leaf senescence pattern exhibited in many Indiana corn fields in 1998 may seem unusual because it is normally not so graphic, but nonetheless may reflect a normal physiological pattern of corn plant maturation and senescence.
Given the importance of leaf area duration to the grain fill period, the rapid leaf senescence evident in many Indiana corn fields in 1998 will likely shave some bushels off the upper limit of yield.