AMES, Iowa – The impacts of recent extreme weather on Iowa’s corn crop have brought many questions to Iowa State University agronomists on what to expect for the rest of the season. Rain has saturated and flooded many of Iowa’s corn fields. Unfortunately, there is little or no research on late-season flooding on corn to determine what the real effects are of this situation, reports Michael D. K. Owen, associate chair of the ISU Department of Agronomy and extension weed scientist.
Owen said any impact from this water on corn yield is purely speculation. For spring flooding, corn can withstand two to four days of flooding without a serious impact. Yet, corn was well into the dent stage across Iowa during the recent heavy rains.
A 1998 publication on wet condition effects included the statement, “…once corn has reached silking, shallow depths of flooding will not cause much damage.” Flooded and saturated soils are a greater concern in the early season because vegetative growth is rapidly progressing and healthy root systems are imperative to take up nutrients, water, etc.
Roger Elmore, ISU Extension corn specialist, said corn in the late reproductive stages is accumulating dry matter for greater kernel weights and this is contributed largely from above-ground movement of carbohydrates. Although root systems are still important at this time, the root mass is naturally declining due to plant maturation taking place.
Elmore said the real impacts and considerations of too much water at this time of year can be summarized as follows:
Shallow, short-term (less than four days) flooding -- Expect limited problems
• Stalk diseases and stalk lodging will increase. Harvest times and efficiency will be compromised.
• Ear diseases and molds (if ears are submerged) will increase and perhaps make the grain unmarketable.
• Poor grain quality may create storage and handling problems.
• Nitrogen status of the soil may change. Carefully soil sampling later in the fall.
• Plant death: some plants may die. See Table 1 for effects of plant death at various late-season growth stages. For example, if an ear contains kernels with a starch line that is half-way down the kernel, the yield loss is 8 percent. Thus, corn would yield 92 percent of what it could have, assuming no other losses occur.
Table 1: Effects of Plant Death at Various Late-Season Growth Stages
Grain Stage Days to Maturity Yield Loss from
Plant Death (%)
Dent 24 35
¼ starch line 19 19
½ starch line 13 8
¾ starch line 7 3
Black layer (maturity) 0 0
Hail also is often a part of these large thunderstorm events, Owen said. At this time in the crop growth cycle, if a plant is broken over or lodged and if that the ear is not harvested, that portion of the crop is lost. Earlier in the season we expect the neighboring plants to compensate for the missing plant. At this time, neighboring plants cannot and will not compensate for the missing plant.
In addition to this, if hail strips leaves yield losses are easily estimated. If half of the leaf area is lost, yields will be reduced around 1 percent. If 100 percent of the leaf area is lost, corn beyond early dent and not yet mature could lose from 8 to 32 percent of yield potential depending on crop growth stage.