Originally published in Purdue Pest Management & Crop Production Newsletter (14 June 1996)

More Thoughts on Stunted, Yellow or Purple Corn

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

Early-season stand establishment of corn is critical to achieving maximum yields possible for any given year, perhaps especially in a year where so many obstacles have been placed in the path of corn growers. Last week I glossed over the causes of corn that's every color but green. This week I figured I should elaborate some on diagnosing stunted, yellow or purple corn.

My definition of 'early-season stand establishment' is that time period between germination and about knee-high corn. This is the period during which the permanent (nodal) root system becomes established.

Successful establishment of the permanent root system is a key factor in a corn plant's ability to endure weather stresses later on in the growing season. Unsuccessful establishment of the permanent root system will cause stunting, and in some cases death, of young corn plants. In addition, if the seed, seed roots, or mesocotyl are injured prior to establishment of the permanent root system, the likelihood of stunting or plant death is even greater.

So, when you troubleshoot a field of stunted yellow or purple corn, concentrate on learning what has gone on below ground. Using a spade or shovel, carefully dig up stunted plants AND healthy plants, carefully remove the soil from the roots and compare...

The condition of the seed.

Prior to about knee-high, the planted seed of healthy plants should be in relatively good shape. The kernels may be shriveled as result of the young seedling using the food reserves contained therein, but otherwise should be relatively 'clean'.

Rotten, mushy, discolored seed suggests fungal or bacterial rots. Tiny 'pin holes' in the seed suggests wireworm feeding. Obviously hollowed-out seed suggests seedcorn maggot feeding.

Relatively firm but shriveled seed with surface fungal growth suggests (Nielsen's observations) that germination and emergence were greatly slowed by cool and/or wet soils, crusty soils, or compacted soils, especially where the seed was unusually small or of poor quality. Seed that appears 'corroded' or 'burned' suggests damage from excessive amounts of starter fertilizer.

Seed that germinated, then lost 'vigor' or died shortly after the coleoptile emerged from the seed may suggest injury from certain planter-box seed treatments containing the insecticide lindane, especially where the seed treatment was not thoroughly mixed throughout the seed hopper AND when conditions were not conducive for rapid germination and emergence.

The condition of the mesocotyl.

Prior to about knee-high, the mesocotyl that connects the seed and crown should remain firm and white. If the mesocotyl is injured before the permanent root system is firmly established, stunting or plant death will occur. Discolored and/or mushy mesocotyls suggest fungal or bacterial rots. Mesocotyls with missing chunks of tissue were likely injured by soil-borne insects like white grub. Mesocotyl growth that is corkscrewed or swollen suggests physical restriction by soil crusts or planter furrow compaction, herbicide injury, or simply cold temperatures.

The condition of the permanent roots.

Permanent (nodal) roots arise in sets from individual nodes (joints) of the stalk. Each set will consist of four or more individual roots equally spaced around the circumference of the stalk. Four or five sets of permanent roots originate from below-ground stalk nodes, with two or three sets originating from stalk nodes above ground.

Prior to knee-high, the number of sets of permanent roots will usually be one less than the number of leaves with leaf collars (Nielsen's observations). For example, a 4-leaf collar plant will usually exhibit 3 sets of permanent roots. If you don't find this relationship (e.g., 4-leaf collar plants with only 2 sets of permanent roots), then you know conditions have not been good for root development.

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 fungal infection.

Permanent roots that appear 'stubbed off' and shriveled, but NOT eaten, suggest excessively dry surface soils (fat chance this year!). Permanent roots that are uniformly discolored (yellowish or brownish) suggest excessively wet soils (Bingo!) or excessively low soil pH. Permanent roots whose tips appear 'burned' off suggest injury from excessive amounts of starter fertilizer.

Return to the the Chat 'n Chew Cafe.

The Corn Growers Guidebook , a WWW resource for corn management systems in Indiana and the eastern CornBelt.

Purdue University Agronomy Extension WWW Home Page.

Purdue Agronomy On-Line! , Purdue's Agronomy Department WWW Home Page.

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