Uneven Corn FieldsR.L. (Bob) Nielsen
Agronomy Department , Purdue University
West Lafayette, IN 47907-1150
Internet address: firstname.lastname@example.org
The buzz at Paul's Pretty Good Pastry Shop late last week centered around corn fields that had come up just fine and looked nice and uniform early on, but have since taken a turn for the worse, especially during the recent hot spell. My own windshield surveys in the last few days confirm that some fields simply look ugly in their unevenness in color and height. What are some of the reasons for this sudden turn of events?
First of all, remember that successful germination and emergence do not guarantee continued success in the development of a corn crop. The second hurdle for that crop is to become "well established" as it continues on its way towards the critical pollination period. Becoming "well established" revolves around the ability of the crop to develop an extensive root system.
An otherwise perfect-looking field can turn "ugly" almost overnight. The causes of such a quick turnaround almost always result from some sort of limitation of root development. Uneven development that is unrelated to uneven emergence often begins to appear some time after growth stages V4 to V6 (4- to 6-leaf collars) when root development normally begins to speed up dramatically.
In such fields, check for limiting factors such as soil compaction, herbicide injury, low soil pH, poor drainage, or root diseases. The effects of such root-limiting factors are usually accentuated in the presence of excessive heat like much of Indiana has experienced during the past week.
Permanent roots developing horizontally instead of a downward angle suggest the presence of severe soil compaction. Permanent roots (and/or seed roots) developing primarily in the planter furrow suggest the presence of severe sidewall compaction by the planter's double-disc openers.
Visible leaf rolling has been a common correlated symptom of compaction in heat-stressed fields late last week as the restricted root system could not keep up with the transpiration load of the plants. Leaf rolling has also been evident in those lower-lying areas of fields where corn root growth was previously restricted by early excessively wet soils.
Permanent roots that are 'stubbed off' AND appear to have been fed upon suggest grub or rootworm larvae damage. Permanent roots that are disfigured (swollen, club ends, excessive secondary root development or 'bottle-brushing') suggest herbicide injury. Permanent roots with scattered discolored areas, with water-soaked lesions, suggest a disease infection.
Permanent roots that appear 'stubbed off' and shriveled, but NOT eaten, suggest excessively dry surface soils. Permanent roots that are uniformly discolored (yellowish or brownish) suggest excessively wet soils or excessively low soil pH. Permanent roots whose tips appear 'burned' off suggest injury from excessive amounts of starter fertilizer.