Several areas in south-central and central Nebraska have been hit with severe storms, with rainfall reported anywhere from 3 inches to more than 10 inches overnight July 8. Some areas fared relatively well. Others, not so much.
For some producers, the start to the growing season was delayed due to flooding. Now, they may be facing it all over again.
At the beginning of the growing season, the major concerns and questions asked pertained to saturated soils and delayed planting. With the exception of some fields taken as prevented planting, most of the fields have been planted and are growing quite well in the area.
Currently, the question for some producers is: how long will the crop survive in standing water?
Flood damage in corn depends on several factors:
1) growth stage and development,
2) frequency and duration of flooding, and
3) air-soil temperature during flooding.
Crop survival depends on environmental stress and nutrient availability. In flooded fields, or fields with excessive ponding, lack of oxygen to the roots can be an issue and can harm plant growth and development.
Less oxygen tends to mean decreased root volume, reduced water and nutrient uptake, and toxic by-products caused by microorganisms in the soil.
Corn growth and development is quite variable across the state, ranging from early vegetative stages to nearing tasseling in the next week or two. If anyone planted late, or planted corn to be chopped for silage on prevented planting acres, their corn may be at the V6 growth stage (six visible leaf collars) or smaller.
If this is the case, plants can only survive under water for 2-4 days if temperatures are cool. Once temperatures exceed 77°F, they might not survive more than 24 hours. For corn in the V7 to V10 growth stage, their roots are more established and they are more capable to survive flooding.
Research has shown that plants in this stage of development can survive 7-10 days if temperatures are not exceeding 86°F.
If flooding occurs when plants are reaching pre-tassel through silking (VT—R1), yield losses may occur.
This is a very sensitive time for the plant when pollination is occurring. Excess flooding can reduce nutrient uptake and successful pollination if standing water is present longer than 2-4 days.
Excessive flooding and water movement can lead to soil loss and nitrogen leaching. Corn plants take up about 60% of their nitrogen needs between V8 and VT/R1.
Scout fields to determine if nitrogen loss is an issue and add supplemental nitrogen via sidedress or fertigation, depending on the size of the corn and equipment available. Another major concern at this point for corn is diseases that can develop following a flood.
Symptoms may not show up until later in the growing season, but certain diseases to look for in flooded fields include crazy top, fungal stalk rots, and bacterial stalk rots. Excessive rains and humid conditions may also lead to foliar fungal diseases this year, so scout early and scout often this summer.
Flood damage in soybeans is quite similar to corn in that it depends on:
1) growth stage and development,
2) frequency and duration of flooding,
3) air-soil temperature, and
4) how quickly the field dries out after the flood.
Submerged soybeans can generally survive for 48-96 hours. However, this is dependent on air temperature, humidity, soil moisture, cloud cover, and soil texture (how quickly it will drain).
Higher temperatures and saturated soils prior to flooding increase plant mortality due to high respiration rates and less oxygen available to the roots. If fields are flooded for 4-5 days, plants may develop fewer nodes and as a result will be shorter.
If fields are flooded for more than 6 days, there may be stand and yield losses. The longer it takes a field to dry out, the more yield loss that may occur. If soybeans were at flowering, yield losses will be greater, especially on poorly drained soils.
Yield losses increase once soybeans reach the R3 to R5 growth stages. Like corn, soybeans may also be susceptible to diseases and show symptoms once floodwaters subside. Two common diseases that might be present later in the growing season include pythium seed and root rot, and phytophthora root and stem rot.
Phytophthora can kill plants at any growth stage while pythium tends to subside once plants are past the V5 growth stage. Again, scouting will be important this year in fields that sustained flood damage.
For producers, homeowners, and business owners that were impacted by the flood this week, don’t be afraid to reach out if you need help. There are several resources available online at https://flood.unl.edu/ for people who wish to learn more about recovering after a flood.
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