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Weed Survey — Postplant

Soon after planting, survey the cornfield to identify germinated weeds. Weeds compete with corn for light, nutrients, and water, especially during the first 3 to 5 weeks following emergence of the crop. Getting a realistic picture of the weed species present, their growth stage, and numbers is necessary for determining the best management methods, especially before corn stalks are 6 to 8 inches high, which is when weeds begin to impact corn yields.

Recording weed survey results assists in weed management decisions, including if management is needed, herbicide choice, and cultivation practices. Information collected over a period of years tells you how weed populations are changing and how effective your management operations have been.

How to survey

  • Walk through each field in a random pattern.
  • Rate the degree of infestation for each weed species on your weed survey form. Indicate the growth stage of the weed (seedling or mature). Sketch a map of the field and mark areas with major weed infestations.
  • Use either a numeric scale from 1 to 5 (1 being the lightest, 5 being the heaviest), or rate the degree of infestation as "light," "medium," or "heavy."
  • Check fencerows, ditch banks, field edges, and wet spots as these may be problem areas for weed growth and, especially field edges, a potential source of wind-disseminated seeds. Also, check weed infestations in adjacent fields.
  • Sketch a map of the field and mark areas with major weed infestations for follow-up control action, noting carefully the location of weeds producing seed.
  • Pay particular attention to perennial weeds. Record the dominant species.

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Statewide IPM Program, Agriculture and Natural Resources, University of California
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