Photosynthetic stress + Grain Fill = Stalk Rot Potential?R.L. (Bob) Nielsen
Agronomy Department, Purdue University
West Lafayette, IN 47907-1150
Internet address: firstname.lastname@example.org
Some of the state's corn crop has been under the strain of heat and drought stress during pollination and now during its early grain fill period. What effects can such prolonged stress have on the development of stalk rot later in the season?
The corn plant tries to defend itself from excessive evapotranspiration during heat and drought stress by rolling the leaves tightly. While this defense mechanism is effective, photosynthesis is also reduced during the process. This compromise between reduced water loss (good) and reduced photosynthetic rates (bad) is acceptable for short-term droughty periods. However, prolonged drought stress and the resulting prolonged photosynthetic stress can cause not only outright yield losses, but also increased stalk rot development later in the season.
Prolonged photosynthetic stress during grain fill results in fewer carbohydrates available to the developing ear. In response, the corn plant will typically respond to the shortage of photosynthate by remobilizing carbohydrates from the leaves and stalk to the developing ear. While this "warehouse" of carbohydrates is nice insurance against the effects of photosynthetic stress, their removal from the stalk tends to lower the plant's resistance to root rot and, subsequently, stalk rot fungi.
Growers should begin inspecting stressed fields for stalk rot development in mid- to late August. Soft stalks resulting from stalk rot development can be detected by pinching the lower 2 or 3 stalk internodes with your fingers. Healthy stalks will not collapse, rotted stalks will collapse easily. If significant stalk rot development is detected, plan on harvesting the field soon after the grain is physiologically mature (development of black layer, about 30% grain moisture).