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Cool temperatures and wet conditions can put stress on corn germination and emerging seedlings. This may cause some concern about reduced corn stands. Before deciding to replant, evaluate the stand for population and uniformity. Next, compare yield potential of the existing stand with yield potential of the replant, as well as insurance or government program restrictions. Finally, if the decision is made to replant, consider various management practices discussed in this ALERT to help optimize yield potential.
Evaluating the Existing StandWhen evaluating corn stands, only count plants that have a good chance of survival. Observe the uniformity of the stand across the field to decide whether replanting the entire field or portions of the field is justified. Spotting in without destroying the existing stand is not recommended3. There may be low areas in fields that will not survive, while the rest of the field will have a good stand. Replanting only the drowned out areas may be a viable option. Carefully evaluate the field for replant options.
One way to evaluate corn stands is to count the number of plants in a length of row equal to 1/1,000th of an acre based on row width (Table 1). Multiply the number of plants by 1,000 to get the plants per acre. Repeat the process in several locations in the field.
A more accurate method is to 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 2 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. Because a longer row length is counted, the samples are more representative and fewer locations are required.
Utilize the same factors for both 30-inch twin- and single row stand counts; however, the plants in both the twin rows should be counted.
Deciding Whether to ReplantAfter taking stand counts, consider the yield potential of the current stand, compared to the yield potential of the target replanting date and population, and the costs associated with replanting. Table 3 provides the percent of maximum yield expected based on final, uniform plant stands and planting dates. Please keep in mind that Table 3 is based on data from Illinois and Indiana, therefore the potential yield loss for the later planting dates in Michigan is likely to be more than what is represented in Table 3.
When the Decision is Made to ReplantFirst, the existing stand should be removed. Tillage is an option in many cases, and should be done at an adequate depth to properly control the original stand. Depending on the growth stage of the original stand, two tillage passes may be necessary. If a pre-emergence herbicide has been applied, tillage may decrease the efficacy of the herbicide by placing it deeper than ideal for satisfactory weed control. Additionally, tillage prior to replanting may result in loss of soil moisture. In drier areas, and where soil conditions allow, a more favorable option might be applying a herbicide to remove the original stand and then replanting without tillage. Roundup® brand agricultural herbicides are also an option when the original stand does not contain the Roundup Ready® Corn 2 trait or Roundup Ready® 2 Technology. If the original stand does contain the Roundup Ready® Corn 2 trait or Roundup Ready® 2 Technology, the tank mix options in Figure 1 can provide control of the original stand. The original plants must exhibit growing green tissue and two to four leaves for the herbicides to be effective. Complete kill may take up to 21 days after application.
Second, determine which relative maturity (RM) to use when replanting. As planting occurs after May 1st, corn requires approximately 1.6 fewer growing degree days (GDDs) per day of delayed planting to reach flowering4. GDDs required to reach physiological maturity, or black layer, decreases approximately 6.8 GDDs per day of delayed planting after May 1st4.
Third, decide on a management practice to protect against corn rootworm and other soil insects, as well as European Corn Borer (ECB). Most soil insecticides can not legally be applied twice in the same growing season in the same location in a field. Growers can replant over the old row and expect some control from the first application of soil insecticide. Another option is to use a different soil insecticide when replanting. A third option is to replant with corn containing the Genuity® family of traits. Depending on region and insect pests present, Genuity® SmartStax® RIB Complete™ and Genuity® VT Double PRO® RIB Complete™ corn blends, and Genuity® VT Triple PRO® Corn offer multiple modes of action for protection against a broad spectrum of insects. Later planted corn is more susceptible to second generation ECB. Research from The Ohio State University suggested significant advantages in overall yield and consistency of yield for corn with the corn borer protection trait compared to their conventional counterparts, when planted in late May and early June3.
Finally, later planted corn has a greater chance of being exposed to heat and drought stress during pollination. This risk can be managed by selecting corn with heat and drought tolerance and early flowering.
1Nafziger, E.D. et. al. 2002. Illinois agronomy handbook, 23rd edition. University of Illinois Printing Services. Urbana, IL. 27-33.2Nafziger, E.D. et. al. 2009. Illinois agronomy handbook, 24th edition. University of Illinois Board of Trustees. Urbana, IL. 24.3Thomison, P. 2005. Replant considerations: hybrid selection issues. The Ohio State University. C.O.R.N. Newsletter 2005-13. http://corn.osu.edu (verified 4/11/2012)4 S. Brouder et al. 2012. Corn & soybean field guide. Purdue University.
Monsanto Company is a member of Excellence Through Stewardship® (ETS). Monsanto products are commercialized in accordance with ETS Product Launch Stewardship Guidance, and in compliance with Monsanto’s Policy for Commercialization of Biotechnology-Derived Plant Products in Commodity Crops. This product has been approved for import into key export markets with functioning regulatory systems. Any crop or material produced from this product can only be exported to, or used, processed or sold in countries where all necessary regulatory approvals have been granted. It is a violation of national and international law to move material containing biotech traits across boundaries into nations where import is not permitted. Growers should talk to their grain handler or product purchaser to confirm their buying position for this product. Excellence Through Stewardship® is a registered trademark of Biotechnology Industry Organization. B.t. products may not yet be registered in all states. Check with your Monsanto representative for the registration status in your state. IMPORTANT IRM INFORMATION: RIB Complete™ corn does not require the planting of a structured refuge except in the Cotton-Growing Area where corn earworm is a significant pest. Genuity® SmartStax® RIB Complete™ and Genuity® VT Double PRO® RIB Complete™ corn are blended seed corn products. See the IRM/Grower Guide for additional information. Always read and follow IRM requirements. Individual results may vary, and performance may vary from location to location and from year to year. This result may not be an indicator of results you may obtain as local growing, soil and weather conditions may vary. Growers should evaluate data from multiple locations and years whenever possible. ALWAYS READ AND FOLLOW PESTICIDE LABEL DIRECTIONS. Roundup Ready® crops contain genes that confer tolerance to glyphosate, the active ingredient in Roundup® brand agricultural herbicides. Roundup® brand agricultural herbicides will kill crops that are not tolerant to glyphosate. Tank mixtures: The applicable labeling for each product must be in the possession of the user at the time of application. Follow applicable use instructions, including application rates, precautions and restrictions of each product used in the tank mixture. Monsanto has not tested all tank mix product formulations for compatibility or performance other than specifically listed by brand name. Always predetermine the compatibility of tank mixtures by mixing small proportional quantities in advance. Genuity and Design®, Genuity Icons, Genuity®, RIB Complete™, Roundup Ready 2 Technology and Design®, Roundup Ready®, Roundup®, SmartStax®, VT Double PRO®, and VT Triple PRO® are trademarks of Monsanto Technology LLC. Leaf Design℠ is a servicemark of Monsanto Company. LibertyLink® and the Water Droplet Design® are registered trademarks of Bayer. Herculex® is a registered trademark of Dow AgroSciences LLC. Select Max® is a registered trademark of Valent U.S.A. Corporation. Respect the Refuge and Corn Design® and Respect the Refuge® are registered trademarks of National Corn Growers Association. All other trademarks are the property of their respective owners. ©2012 Monsanto Company. 04262012EJP