Iowa State University Extension and Outreach 9/7/16

Brian Lang
Extension Agronomist


The flash flooding in northeast Iowa has left many producers wondering what to do next. In many areas, the flooding of 2016 reached record levels.
Past experience has shown us that if flood waters got above ear height, the ears were likely ruined. That assessment was correct for the floods of 2008 and 1993, but corn was flooded near tassel stage. In those cases, ears under water were ruined, basically turning to mush within a week.

It is a different story this year. The August 24 flood occurred with most corn at early dent stage. In general, ears from these flooded fields still look to be in good condition, so far. The flood waters appeared to drop quickly, which in most cases will minimize potential problems. Here are some factors to watch.

Hybrids with tighter husks held out water and silt deposits from the kernels better. Loose husks and ears that extended beyond the husk have silt deposits on the kernels, more flood water exposure to the ear and cob, which make them at higher risk of mold development.

Many of these plants have husks totally covered in silt and nearly sealed up tight with a “mud” cover. What will this mean for dry-down?  Will it retain more moisture and enhance potential mold development, or just slow dry-down? Time will tell.

Kernels damaged prior to the flood (i.e. insect feeding, bird damage, etc.), then exposed to flood waters are at higher risk of mold development. A common fungal development in corn following a flood is smut, which is relatively harmless. Smut does not develop mycotoxins, and is actually grown and marketed as a food delicacy. Other fungi (ear molds) may also develop by harvest time, and ears will need to be assessed before harvest. If mold is found then grain should be tested for potential mycotoxin presence, identifying which kind and what concentration.

Normal corn development from early dent stage has about four more weeks to physiological maturity (black layer). There are still several unknowns, including: 1) Various degrees of silt-covered corn will interfere with photosynthesis and reduce kernel fill, resulting in light test weight. Silt-covered plants will add challenges to combine function; 2) Prolonged saturated soil could prematurely kill corn, and/or enhance development of root and stalk rot affecting standability and kernel fill, resulting in light test weight and harvest problems; and 3) Will silt-covered husks eventually open up for dry-down, or remain tight, retain moisture and enhance mold development? Ears will need to be assessed for mold development before harvest.

Corn Silage
Silt deposits on the plants make them useless for silage.  Early dent is near time for corn silage harvest, and it’s just not possible to get sufficient rainfall to wash the silt off of the crop. For shallower flood water areas, set the chopping head above the height of silt deposits on the plant.
The silt covering flooded soybeans to various degrees will block photosynthesis, resulting in reduced grain fill and seed size. Prolonged saturated soil could prematurely kill the soybeans or enhance development of root rot affecting standability and kernel fill, resulting in reduced grain fill. Silt covered plants and lodged plants will add challenges to combine function.
Alfalfa can survive a few days under water, and this flooding has receded quickly. Although, alfalfa does not tolerate extended saturated soil conditions as well as clovers or forage grasses.

However, silted forage is useless for feed and would require additional rains to wash silt off the plants.

If a significant area of the field is ‘silt-damaged’, and you want another crop this fall, chop it back onto the field. The regrowth will be normal. By the time field equipment can re-enter a flooded field, we should have a good idea as to what condition the crop is in.

For more information on flood recovery for farms and homes, contact your county ISU Extension office or visit