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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.
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 (ppa). 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.
Second, determine which relative maturity (RM) to use when replanting. As planting occurs after May 1, 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 14. In southern Illinois, typically corn can be planted through the end of May without switching to an earlier RM. Since fewer GDDs are required to mature corn and since they are adapted well to southern Illinois, several of the 108 to 112 day hybrids are good options to plant through the first two weeks of June. After the middle of June is the time to start considering options such as switching to an earlier RM corn that might not be as well adapted to this geography or planting soybeans. However, final stands of 20,000 ppa can produce acceptable yields compared to replanting full stands in June, especially south of the glacial moraine.
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 cannot 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.
Sources: 1 Nafziger, E.D. et. al. 2002. Illinois agronomy handbook, 23rd edition. U of I Printing Services. Urbana, IL. 27-33.2 Nafziger, E.D. et. al. 2009. Illinois agronomy handbook, 24th edition. University of Illinois Board of Trustees. Urbana, IL. 24.3 Thomison, P. 2005. Replant considerations: hybrid selection issues. The Ohio State Univ. C.O.R.N. Newsletter 2005-13. http://corn.osu.edu (verified 4/11/2012)4 S. Brouder et al. 2007. Corn & Soybean Field Guide. Purdue University5 Wiebold, W. and R. Massey. 2012. Corn and Soybean Replant Decisions.
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. Ignite® and 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. 04172012EJP