Top leaf death or "dieback" in corn
Death of top leaves can occur throughout the year as a direct result of a combination of excessive heat and drought stress as plants struggle to maintain leaf health during periods of soil moisture deficits and high transpiration before or during the grain fill period. Such leaf death is usually preceded by a gray-green color and wilting of the upper leaves. This drought-related pattern of upper leaf senescence also often affects all plants within severely drought-stressed areas of affected fields. In 2011, upper leaf death in response to heat + dryness occurred in some late-planted fields before they even reached the pollination stage.
Death of top leaves can also be the result of European corn borer (ECB) or Southwestern corn borer (SWCB) tunneling damage to the upper stalk itself or girdling of the leaf sheath attachments at the stalk nodes. Such insect-related patterns of upper leaf senescence usually occur more randomly from plant to plant rather than affecting all plants within a field or area of field. This cause of damage to the upper canopy is less common today than 20 years ago because of the wide-spread adoption of Bt-corn borer trait hybrids, but can obviously still occur in fields planted to non-Bt trait hybrids.
Finally, death of upper leaves and stalks can be the result of infection by anthracnose (Lipp & Mills, 2001; Robertson, 2007). One of the distinguishing symptoms of anthracnose "die-back" or "top-kill" is the presence of black lesions visible on the outer stalk tissue behind the leaf sheaths (Robertson, 2007). This fungal disease can be particularly damaging if it significantly shortens the grain-filling period resulting in premature kernel black layer development . Such disease-related patterns of upper leaf senescence usually occur more randomly from plant to plant rather than affecting all plants within a field or area of field.