Originally published in the Chat 'n Chew Café (3 Jun 1998). Also published in the Purdue Pest Management & Crop Production Newsletter (5 June 1998)

Erotic Corn Fields

R.L. (Bob) Nielsen , Agronomy Department , Purdue University, West Lafayette, IN 47907-1150
Internet address: rnielsen@purdue.edu

I got word this week that there has been a lot of talk down at the Chat 'n Chew Café about "erotic" corn fields. I suspect that the actual topic of discussion centered around "erratic" corn fields, those fields with uneven population or height that are so prevalent around the state this year. Last week, I encouraged folks to begin spending some time in their fields taking notes about emergence and growth. This week, I want to fill in some more detail on these "erratic" fields of corn.

Uneven Germination & Emergence

Uneven plant populations throughout a field result from some combination of problems with planter operation, germination and emergence. The success or failure of the latter two events depend on the adequacy of soil moisture and temperature (seedbed), the degree of seed-to-soil contact, and the absence or presence of soil pests.

Differences in soil temperature between light and dark soils or wet and dry soils may be significant enough to influence germination and emergence. April plantings this year were often affected by this variability.

Differences in soil moisture between low and high ground or well- and poorly-drained soils can also influence germination and emergence. Extremes in either direction, wet or dry, can limit germination. April and May plantings this year often exhibited the effects of this variability where rainfall was excessive or limiting.

Seed-to-soil contact is important for the germination process because of the need for the seed to absorb sufficient moisture to initiate the process. It should be no surprise that seed-to-clod contact, seed-to-dust contact or seed-to-air contact (open furrows) is not conducive for rapid and uniform germination. Variability for the degree of seed-to-soil contact throughout a field will easily result in uneven germination and, consequently, emergence. As with the other factors, April and May plantings this year often occurred in seedbeds that exhibited varying degrees of cloddiness and soil moisture, while open planter furrows have been common in no-till fields planted on the wet side.

Soil insects have not been a prevalent problem with this year's plantings, but soil-borne fungal diseases have been troublesome in many fields. As H. Walker Kirby, Extension plant pathologist at the Univ. of Illinois, has described (Illinois Pest & Crop Bulletin, May 15 & 29); the primary pathogen involved appears to be the fungus Pythium, which is favored by wet soils and cool weather.

It has not been uncommon this year for significant rainfall to occurr after plantings. Even where germination was successful, subsequent emergence of the crop has been restricted where dense surface soil crusts developed. As they say in comedy clubs, timing is everything. The effects of soil crusting depends on the timing of the emergence of the coleoptiles or "spikes" of the corn seedlings. Where emergence had not yet occurred before the development of the crust, the penetration of the coleoptiles were often limited severely enough that leaf emergence occurred below ground. Where the coleoptiles were almost at the soil surface or just beginning to emerge when the crusts developed, subsequent completion of emergence often occurred successfully.

Development of the Plant

Successful germination and emergence does not guarantee continued success in the development of the crop. Assorted limiting factors such as excessive or deficient soil moisture, disease or insect pressure, compaction from tillage traffic or planting in wet soils, variable soil temperatures, and herbicide injury can all retard the subsequent development of a corn crop.

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.

Permanent roots that are developing horizontally instead of downward at an 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.

Permanent roots that are 'stubbed off' AND appear to have been fed on 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.

Corn Growers Guidebook

For other information about corn, take a look at the Corn Growers Guidebook on the World Wide Web at http://www.agry.purdue.edu/ext/corn/

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