Michigan Corn, Soybeans: Evaluating Storm-Damaged Crops

Heavy rains, strong winds, hail and even tornadoes leave their mark on fields across the Midwest every year. If your farm is in the path of one of these storms, there is not much you can do, except seek shelter and assess the damage when the coast is clear. As the sun starts to peak through the clouds, a drive around the area is warranted to see what damage occurred.

But don’t be tempted to get the planter out; it always looks the worst right after the storm. Most experts recommend waiting three to ten days before making a full assessment of the crop damage.  By this time, you can easily tell which plants will survive.

Hail Damage

Hail is hard on crops; torn leaves broken stalks, and plants stripped nearly bear. Right after the storm the fields are at their worst – wait a couple of days then evaluate.

Corn from emergence until seven leaves are fully emerged has a good chance of surviving a hail storm with very little stand or yield loss. However, once the growing point is above the soil surface and throughout the rapid growth stage, the corn plant is most vulnerable to hail damage. When evaluating corn for hail damage, it is important to determine the stage of growth, the extent of damage to the stand, leaves and the stalk.

To predict soybean loss, first determine the stage of growth at the time of the damage. According to Mike Staton, Michigan State University Extension educator, soybeans in the vegetative stage will suffer minimal yield loss due to defoliation unless leaf tissue has been completely removed.

However, once soybeans have reached the reproductive stage, the assessment will also include the degree of plant damage. Stand reduction, leaf defoliation, stem damage, and possibly pod damage, all impact potential yield in soybeans in the reproductive stage. Each will need to be evaluated and the percentage loss identified.

To assist producers in accurately determining loss due to hail, refer to the Michigan State University Extension article, “Assessing hail damage to soybeans in the early vegetative stages,” or the University of Nebraska-Lincoln Extension Publication EC-128, “Evaluating hail damage to soybeans.”

Hail damage to corn. Photo credit: Phil Kaatz, MSU Extension

Hail damage to corn. Photo credit: Phil Kaatz, MSU Extension

Hail damage to soybeans

Hail damage to soybeans. Photo credit: Phil Kaatz, MSU Extension

An accurate estimation of stand is important regardless of crop or stage of growth; once plants have recovered from the initial shock of the storm and you can see what plants will survive, it is time to determine the stand. There are two methods that can be used: counting viable plants in a row equal to 1/1000 of an acre, or counting viable plants within in a sampling area, i.e. the hula hoop method.

To begin, select the method that best fits the production system being evaluated. As a general rule, the hula hoop method works well for drilled soybeans, and the length method works well for rows. Tables 1 and 2 are from the Michigan State University Extension article, “Assessing soybean emergence”, by Mike Staton.

Table 1. Length of row required to equal 1/1,000 of an acre

Row width (in inches) Length of a single row to equal 1/1,000 of an acre
15 34 feet and 10 inches
20 26 feet and 2 inches
22 23 feet and 8 inches
28 18 feet and 8 inches
30 17 feet and 5 inches

To use the information in Table 1 to estimate the number of soybean plants per acre in 30 inch rows, count the number of plants in 17 feet and 5 inches of row at ten random locations in the field. Simply multiply the average count for the ten locations by 1,000 to get plants per acre. For example, if the average count in the sampled rows was 108, the population would be 108,000 emerged plants per acre.

Table 2. Converting hula hoop plant counts to plants per acre

Inside diameter of hula hoop (inches) Conversion Factor (multiply the number of plants within the hoop by the appropriate factor to calculate plants per acre)
36 6,616
33 7,334
30 8,874
27 10,956
24 13,865

To use the hula hoop method, toss the hoop in ten random locations in the field and record the number of emerged plants within the hoop at each location. Calculate the average and multiply it by the appropriate conversion factor for the diameter of the hoop you are using.

For example, if the diameter of the hoop is 30 inches and the average number of emerged plants is 16, the population is 143,984 emerged plants per acre (16 x 8,874). If the diameter of your hula hoop is not listed in Table 2, you can calculate the conversion factor with the following equation:

Conversion Factor = 43,560 ÷ [3.14 x (the inside hoop diameter in inches ÷ 2)2 ÷144]

If hail has damaged your crop don’t let the early condition of the plants scare you into replanting! Soybeans planted on June 30 are only expected to yield 70 percent of a May 20 planted crop. Corn planted this late in the season will likely not mature. So, wait three to ten days; you might be surprised at how resilient crops can be!

Flood Damage

Plants in flooded fields can survive, but the odds are against them. If water drains away quickly, the plants are not covered by mud or crop residue and the soil moisture returns to normal within a day or so, the plants may survive. Well drained soils increase the odds, but there are fields where at least one of these factors will put plants at risk.

Fully submerged plants are at greatest risk of “drowning”. Respiration of both corn and soybean plants that are underwater will use up the minimal oxygen that is available and the plants will die. This occurs faster with higher temperatures. In fact, corn prior to the sixth leaf stage may die after just 24 hours if temperatures are over 77 degrees Fahrenheit. Soybeans can survive two to four days under water. Cooler temperatures and cloud cover will improve survival.

Corn 26 hours after rain. Photo credit: Marilyn Thelen, MSU Extension

Corn 26 hours after rain. Photo credit: Marilyn Thelen, MSU Extension

Soybeans flood damage

Soybeans 26 hours after rain. Photo credit: Marilyn Thelen, MSU Extension

When waters go down, they often leave plants covered in soil or crop residue. This can decrease the plants ability to conduct photosynthesis further putting the plants’ survival at risk. Oddly enough, the best thing for a “dirty” plant would be another rain to wash the leaves. Taking time to remove crop residue drifts from plants will increase plant survival.

Poorly drained areas of the field may stay too wet for too long. If this occurs, plants may suffer from root rot, resulting in stunted growth, reduced stand and will possibly make plants more susceptible to disease.

Once the water has drained away and three to 10 days have passed, it is time to see what plants have survived and get an accurate stand count. There are two methods that can be used: counting viable plants in a row equal to 1/1,000 of an acre, or counting viable plants within in a sampling area, i.e., the hula hoop method.

To begin, select the method that best fits the production system being evaluated. As a general rule, the hula hoop method works well for drilled soybeans, and the length method works well for rows.

Plants can survive a flood! Getting the water drained off as soon as possible and removing any crop debris will help. By the time you can safely pull a planter into the field, you might be surprised at the number of plants that are alive and well. Assess the stand before you decide to replant.

Wind Damage

Wind can take a toll on crops. Corn in the vegetative and early reproductive stages is most at risk. The two most common ways corn is damage is green snap and root lodging.

Green snap is just like it sounds – the corn plant snaps off under the pressure of the wind. Corn is most vulnerable to green snap during the rapid elongation stage (V8 – tasselling). Conditions favorable for rapid growth, good moisture and heat increase the risk of stalks breakage.

According to Emerson Nafzinger, University of Illinois, the yield effects of green snap is dependent on the number of plants snapped and where the breakage takes place. If it breaks the node just below the ear, dormancy will break and allow the next ear to develop; however, this ear may produce fewer kernels due to decreased pollen.

If the stalk breaks near the ground, no ear will be produced. As a general rule, there is a high potential for loss with green snap.

Root lodging looks like the corn has been “steam-rolled,” or random stalks will be flatted or tipped. Flattened plants suffer a disruption of the root system and disorientation of the leaves. If the corn is at the pollination stage when maximum photosynthetic rates are needed to assure successful pollination, the impact can be negative.

Younger, more flexible corn plants will tip upward, reorienting the leaves. These plants may produce a normal ear. As plants get closer to tassel, the potential yield loss is greater. In a study by the University of Wisconsin where root lodging was simulated, corn lodged at V13-V15 saw a yield reduction of 2-6 percent whereas corn lodged after V17 experienced a 12-31 percent reduction in yield.

We are entering prime season for root lodging. Factors that can increase the risk of lodged corn are:

  • Cool, wet soils leading to shallow root development.
  • Root worm larva feeding – check for root feeding on lodged corn.
  • Too shallow of seed placement.
  • High plant population.
  • Type of hybrid – look for hybrids with a good score for root lodging.

As with all types of storm damage, soon after the storm, the damaged field will look its worst – give the field several days to recover. As corn turns upward, you may notice “goose necking.” Although corn may recover and develop normally, goose necking may result in a more challenging harvest and possible harvest loss.

Wind damage in soybeans is not common, but can occur especially if the plant structure has been weakened. Herbicides with the active ingredient sulfentrazone such as Authority, Canopy XL and Cammand Xtra, can create an area of weakened tissue that may lead to plants snapping off in heavy wind or rain storms according to University of Illinois Extension.

Wind damage usually occurs later in the season when plants have some height. Before considering replant, check to see if there is enough growing season left to make replant a viable option.


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