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 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.”
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.
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.
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!
Resources available to help with field assessments: