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Stalk Borer Update

Stalk borer 

Development of stalk borers is based on climatic temperature. Stalk borers develop whenever the temperature is above 41 degrees. Therefore, the stage of development is estimated based on Growing Degree Days (GDD) Base 41. The formula for a given day is the daily high (minimum 41) plus the daily low (minimum 41) divided by 2 to determine the average temperature for the day. From the average temperature for the day, subtract 41. If the result is a positive number, add it to the GDD of all prior days with a positive result.

Sometimes stalk borers are problems in large parts of fields.

  • Areas of row crop fields with areas of grass or giant ragweed last year may be burned to kill the eggs. See pages 21-22 of the April 7, 1997 Integrated Crop Management Newsletter for details on this strategy.
  • Moldboard or chisel plowing may be used to bury the eggs so that many hatching larvae cannot survive. However, there may be an unacceptable number that survive.
  • Another management alternative is to spray the area with an insecticide with residual activity just prior to egg hatch. Stalk borers begin to hatch at 575 GDD Base 41. See pages 66 - 67 of the May 19, 1997 Integrated Crop Management Newsletter for details on this strategy. Note that once stalk borers have hatched and have moved into the crop plants, there is no effective rescue.
  • If eggs have hatched and larvae have moved into grassy weeds or giant ragweeds, and if the crop has emerged, then killing the weeds with a post emergence herbicide will cause the stalk borers to leave the dead plants and move to the crop plants. If stalk borers are present in weeds, including a labeled insecticide with the post emergence herbicide will kill the stalk borers as they leave the weeds.

    Most commonly, stalk borers hatch in ditches, fencelines, and waterways, where they move into tall grass, such as brome. As the stalk borers develop, they outgrow the grass plant, killing the top of the plant, and then move into nearby crop land, generally corn. Observing the seed head stems of grass in waterways, ditches, and fencelines for signs that they have been killed will provide some guidance on the need to spray the edge rows of corn to kill the stalk borers as they migrate into the field. Start checking field borders once 1,300 GDD Base 41 have accumulated. (In some cases, stalk borers move as soon as 1,000 GDD Base 41, however.) See the June 3, 2011 Integrated Crop Management News for details.

    Following are GDD Base 41 accumulations as of the end of the respective day. Remember that

  • Egg hatch begins at 575 GDD and is complete at 750 GDD Base 41.
  • Stalk borer migration from grassy areas begins at about 1,300 GDD Base 41, about 10% have migrated by 1,400 GDD, and about 50% have migrated at 1,700 GDD. Management decisions must be made before 1,700 GDD have accumulated.

    June

    Burlington

    Cedar Rapids

    Davenport

    Dubuque

    21

    1,896.0

    1,570.5

    1,715.5

    1,446.5

    22

    1,920.5

    1,593.0

    1,741.0

    1,471.5

    23

    1,945.0

    1,614.0

    1,764.5

    1,492.0

    24

    1,971.5

    1,636.5

    1,788.5

    1,515.0

    25

    1,993.0

    1,658.0

    1,810.5

    1,537.0

    26

    2,020.0

    1,685.5

    1,840.5

    1,563.5

    27

    2,052.5

    1,715.0

    1,870.0

    1,595.0

    28

    2,081.0

    1,740.0

    1,896.5

    1,622.0

    29

    2,110.0

    1,767.5

    1,924.0

    1,648.0

    30

    2,149.5

    1,805.5

    1,961.0

    1,684.0

     

    As 1,700 Growing Degree Days (GDD) have passed in all of the counties represented by this page, this page will not be further updated until 2012.

     

    If you have any questions, please feel free to contact the Iowa State University Extension Office.
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    Last Update: July 1, 2011, except the data in the table was last updated the day after the most recent data listed.
    Contact: Virgil Schmitt vschmitt@iastate.edu


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