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Figure 1. Ceased germination because of dry conditions.
Regardless of the time, effort, and precautions that were taken to plant corn and soybean crops, environmental situations, equipment failure, pest activity, and management decisions may have led to emergence issues that make replanting a consideration. However, appearance alone should not be a deciding factor for replanting a crop. Diligent scouting, population measurements, current and future weather forecasts, and economic impact should be considered before a replant decision is made.
Figure 2. Seedling injury from imbibitional chilling.
After planting, environmental factors such as too much or too little rain and cold temperatures can cause emergence issues. Too much rain can cause seeds to rot, particularly if soils are cold and too little rain can cause seeds to remain dormant or sprout and die (Figure 1). Cold temperatures can increase the risk for chilling injury if corn seeds are exposed to soil temperatures under 50º F for an extended period of time and/or experience large swings (25 to 30º F) in daily soil temperatures. Chilling injury can result in failed germination and/or hindered growth of the radical or coleoptile if it occurs within 24 to 36 hours after planting, and corkscrewed mesocotyls and/or leafing out below the soil surface if it occurs during the emergence process (Figure 2).
Figure 3. Comparison of white grub larvae (top): Chafer larva (left), Japanese beetle larva (center), and May or June beetle larva (right). Bottom row: Seedcorn maggot (left), Wireworm (center), and Black cutworm (right).
Figure 4. Symptoms of early season maize billbug feeding.
Additionally, soil insects can stunt or kill young seedlings. Those of particular consideration are white grub, black cutworm, wireworm, and seedcorn maggot larvae (Figure 3). Billbug beetle (Figure 4) feeding on corn and bean leaf beetle (Figure 5) feeding on soybean can be damaging to young plants. Though not an insect, slugs can also be injurious to seedlings (Figure 6).
Figure 5. Bean leaf beetle.
Figure 6. Slug and feeding scars.
Seedling diseases specific to corn and soybean such as Pythium, Rhizoctonia, Fusarium, Penicillium, Stewart’s Wilt, and Phytophthora can infect seedlings and kill or stunt them. Being alert through scouting for diseased plants can help determine if the remaining healthy plant population is sufficient for a revised economic yield goal.
Wheel Method - Count 150 plants and measure the distance from start to finish with a measuring wheel. Divide the number of feet traveled into the appropriate factor in Table 1 to determine plant population. For example, if you walked 94 feet while counting 150 plants in 30-inch rows, the population is 2,613,600 ÷ 94 = 27,804 plants/acre. The process should be repeated several times with the results being averaged.
1/1000th Acre Method - Count the number of plants in a length of row equal to 1/1000th of an acre based on row width (Table 2). Multiply the number of plants by 1000 to determine plants/acre. Repeat the process in several field locations for an accurate estimate. Keep in mind problem spots with known issues should be evaluated separately from the rest of the field.
Hoop Method - This method should be used for drilled crops. Measure the diameter of the hoop, toss it in the field, and count the number of plants inside the hoop (Figure 7). Do this in at least 5 locations in the field. Multiply the average number of plants by the appropriate factor listed in Table 3 to determine the number of plants/acre. Notice that having a diameter of 28 ¼ inches allows you to simply multiply by 10,000 to obtain the number of plants/acre. This size of hoop can be made by cutting anhydrous tubing to a length of 88 ¾ inches and joining it to form a circle.
Figure 7. Count the plants within the hoop and use factors from Table 3 to determine plants/acre.
Deciding to Replant - After taking stand counts, consider the yield potential of the current stand compared to the yield potential of the targeted replanting date and population, and the costs (current crop destruction, replant seed, herbicides, insecticides, labor, equipment, etc.) associated with replanting. Tables 4 and 5 illustrate the percent of maximum grain yield expected from various planting dates and final plant populations, based on uniform stands for corn and soybean respectively.
Should you need additional replanting information, please contact your Asgrow® and DEKALB® brands dealer.
1Illinois agronomy handbook. 2012. 24th Edition. University of Illinois Extension. http://extension.cropsciences.illinois.edu/handbook/. 2Brouder, S.M., et al. 2010. Corn & soybean field guide. ID-179. Purdue University. 3Whigham, K., Farnham, D., Lundvall, J., and Tranel, D. 2000. Soybean replanting decisions. PM 1851. Iowa State University. https://store.extension.iastate.edu/Product/Soybean-Replant-Decisions. Doc ID: 160407075914