Detective Work Helpful In Finding Cause Of Missing Corn
May 21, 2003 10(10):78-79
Joe Lauer, Corn Agronomist
Scout corn early to evaluate stand and check for potential problems. Take some time
to walk each field individually looking for soil compaction, crusting, diseases,
insects, weeds and stand establishment problems. Windshield observations do not
qualify as field scouting. A simple drive-by will not be sufficient, since only
large-scale disasters show up at 55 miles per hour.
When the corn population is economically unacceptable, the earlier a replant decision
can be made, the better. Check corn populations through out the field. Problems
always seem to develop farthest away from the road. Before entering the field, look
over the entire field for areas that appear different. Check those particularly
well when scouting.
Scout fields in a W pattern, checking plant population in several parts of the field.
Look for problem patterns. Is the problem throughout the field? Is there a pattern
to missing corn? Are individual rows missing or emerging erratically? In areas without
corn, determine whether or not seed was planted. Check planting depth. Counting
rows can show which planter row was malfunctioning.
Field areas with pattern problems
Poor stands or seedling vigor are sometimes due to compaction and other field preparation
problems. Patterns relating to wheels or tillage equipment will be visible. Misapplication
of herbicide, herbicide carryover, and excessive nitrogen or potassium fertilizer
in contact with the seed are identifiable problems. Fertilizer salt effects or fertilizer
burn often cause seeds to turn brown or black and very firm. Roots will be nubbed
off with black or brown tips. Ammonia toxicity field symptoms are long or short
strips of damaged plants in rows scattered throughout the field.
Be on the lookout for soil crusting. Soils that work up very fine have greater crusting
potential. If crusting is suspected, and the crop has not yet emerged, use a rotary
hoe, but be careful the operating depth of the spoons does not dig out sprouted
and emerged plants.
Field areas with random problems
Stand losses from insects and plant disease do not follow straight lines, and damage
usually doesn't occur throughout the entire field. Localized or spotty areas with
a poor stand provide a clue that the stand problem is disease- or insect-related.
Examine entire plants as well as the appearance and location of problem areas in
Several fungi, including Pythium and Fusarium, can cause pre-emergence and post-emergence
"damping off" of corn. A rotted, discolored or water-soaked appearance
of the seed or portions of the seedling indicates the presence of a pathogen. Seeds
and seedlings are brown, soft and mushy and may be difficult to find because of
rapid decomposition. Corn seedling diseases are often associated with cold, wet
soils such as are often found in low areas. Diseases can be secondary to damage
caused by other factors.
Damage form several insects tend to be worse when cool, wet soil conditions slow
corn germination and emergence. Look for damage of embryonic tissue on the kernel
tip, or for holes in the kernel. Damaged tissue will quickly turn brown and rot.
Field history can provide clues to the species causing stand reduction. For example,
if a poor stand is associated with heavy manure application or other high organic
matter conditions, then suspect seed corn maggot. A recent history of sod implicates
wireworms or white grubs. These problems cannot be corrected in-season.
However, several species of cutworms can be controlled effectively with insecticide
rescue treatments. Early detection is important, as most species will feed on leaves
before they are large enough to cut plants. Knowing the species, the stage of cutworm
development, and the amount of damage will help determine the appropriate insecticide
treatment. Later planted fields with lots of crop residue and weed growth have the
greatest potential for cutworm damage.
Modern seed corn has better early season vigor than previous hybrids. Once in a
while, seed lots have problems with poor germination and emergence. Suspect this
problem only if planting, insect and disease problems have been eliminated.
Each field has its own set of circumstances, but it usually comes down to two situations
when making a replant decision: the remaining stand and the likely replant date.
Ultimately this decision hinges on which situation will maximize net income. Don't
replant a cornfield without first considering the calendar date and the plant distribution
throughout the field. Consider the nature of the problem if the remaining stand
dictates replanting. For example, a seed treatment may be appropriate when planting
back into an insect problem. Keep records of where stand loss occurs, as problems
tend to repeat themselves in future years.