By Jonah T. Johnson, MS, CPAg, CCA, Southern Ohio Field Agronomist for DuPont/Pioneer
As many of you read farm related publications this fall, the common theme will probably allude to something of “how did we begin with such a good start and end up where we are today?” No one can foresee the future unfortunately, or no one would have planted corn in March and April. The 2012 drought has created quite the predicament for growing corn in Ohio.
As I walk corn fields in southern Ohio, the long-term excessive heat and lack of available water has paved the way for extreme variability in yield, test weight, and ear and kernel size within fields spatially.
Weak ear shanks
Many of the fields that were extremely stressed are exhibiting weak shanks and pinched ear butts. As husks are pulled back on ears, these weak shanks break, dropping ears to the ground. Lodging and ear drop will be most prevalent when the ear reaches physiological maturity. This stage dictates maximum weight from dry matter accumulation and high moisture content, which is 30-35%. The additional weight accompanied by high winds, insect feeding on shanks and other stress accelerate plant maturity and the natural abscission process.
Abscission or “shedding” of ears is controlled by several plant hormones. As the plant reaches maturity, higher levels of abscisic acid and ethylene are produced, resulting in an escalated “ripening” process and a progressive weakening of cell membranes in the zone between the shank and the base of the cob resulting in ear drop. Extreme drought and hot conditions induce elevated abscisic acid levels. This is thought to be the defense mechanism that regulates stomata closure, like pores in your skin, which reduces water loss. As the plant tries to conserve moisture, it’s actually hurting the offspring (ear) by ultimately letting the ear go too soon. Additional stresses such as high winds or insect feeding on the shank also escalate ear droppage. Walk fields to determine which hybrids may exhibit this problem more than others and harvest these as early as possible.
As the corn kernels develop, they essentially become a “bank” where the corn plant deposits mobile sugars it produces through photosynthesis. When the corn plant experiences severe stress (i.e. drought, heat, nutrient deficiency, insect damage, disease, etc.), photosynthetic rates are reduced. To compensate for the lack of photosynthesizing products and respiration being deposited into the corn grain during this time of stress, the corn plant will remobilize stored carbohydrates from the stalk and leaf tissue to meet the intense physiological demand by the developing corn kernels. This process physically and chemically weakens the stalk, increasing susceptibility to stalk rots. Physically push stalks to 20 degrees and/or pinch corn plants 6-8 inches above the ground. If you can easily compress the stalk and push plants over, you have a potential problem. Rots such as Gibberella, Diplodia and Anthracnose may be the culprit.
For more visit: www.agronext.iastate.edu/corn/docs/corn-field-guide.pdf
Aspergillus ear rot and aflatoxins
This ear rot thrives in hot and dry conditions. Caused by the fungus Aspergillus flavus, this ear rot is observed as a fluffy, yellow-green mold beginning on the middle of the ear and extending to the tip. This is most severe when drought (especially drought during pollination and grain fill), extreme heat, or insect injury occurs; it grows best on corn at 18 to 18.5% grain moisture. Aspergillus can produce aflatoxin, a very potent group of carcinogenic, cancer-causing toxin. However, just because the fungus is present does not mean aflatoxin is present.
A sound sampling protocol involves stripping back 80 to 100 random ears across a field while noting occurrence of the green, fluffy mold. Make sure to properly identify the ear mold. Suspected samples should be sent to a credible lab for analysis to determine whether aflatoxins are present in the grain and whether they exceed current U.S. FDA thresholds.
For more visit: http://www.rma.usda.gov/fields/il_rso/2012/aflatoxin.pdf and http://www.fda.gov/Food/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/ChemicalContaminantsandPesticides/ucm077969.htm#afla.
I recommend walking your fields to test stalks for integrity, inspect plants for weak shanks and potential ear drop issues, and also scout for corn ear rots. Begin harvest at 22 to 25% moisture and dry grain immediately down to 15% moisture content.