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Dectes Stem Borer

 
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Dectes Stem Borer

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Injury and Pest Symptoms of Dectes Stem Borer

Larvae damage soybeans by: 1) tunneling inside the stem and reducing yield production capacity, and 2) girdling, which causes plants to lodge

  • Dectes stem borer larvae girdle stem 1 to 2 inches above soil line
  • Girdling, and subsequent lodging, are most severe in early planted, short-season soybean varieties
Decetes stem borer larva in soybean stem
Soybean stems girdled by larvae

Pest Status and Importance

  • Minor soybean pest in most states, but fields in some areas may have approximately 100% of plants infested
  • Yield losses range from 7 to 12% in individual plants
  • Girdled plants may snap off at slightest pressure, causing plants to lodge prior to harvest

Pest Facts

  • Common names: Dectes stem borer, soybean stem borer
  • Latin name: Dectes texanus, family Cerambycidae
  • Description
    • Adult: gray-colored beetle with long black-and-gray banded antennae; length is ½ inch
      (13 mm)
    • Larva: creamy white to dull yellow in color, without legs, ½-inch long with "accordion-style" segments
    • Egg: very small, white-colored egg laid inside soybean petiole where female cuts a scar (see photo below)
Decetes stem borer egg scars on soybean stem
Adult Decetes stem borer
Decetes stem borer larvae

Larvae of Dectes Stem Borer.

Life History

  • Larvae pupate in the spring inside soybean stem
  • Adults emerge from stems during late June to late July in Kansas
  • Adults may live to September
  • Sunflower is the preferred host; cocklebur and giant ragweed are also used as larval hosts
  • Soybean is a secondary host for larvae
  • Adults live an average of 23 days on soybean, but 53 (males) and 76 (females) days on sunflower
  • Females lay eggs primarily in leaf petiole
  • Larvae tunnel down leaf petiole and into main stem
  • Larvae complete 4 stages
  • Larvae create an internal girdle of the stem near soil line and plug the tunnel below the girdle with frass
  • Larvae are cannibalistic; only one larva overwinters in base of stem
  • 1 generation occurs per year

Origin and Distribution

  • Native to North America from Atlantic seaboard to Great Plains; primarily a pest in central Great Plains and lower Mississippi River Valley
Dectes stem borer distribution in soybeans in the lower Mississippi Valley

Dectes stem borer distribution in soybeans in the lower Mississippi Valley (Tindall et al. 2009. J. Insect Science)

Integrated Pest Management Practices

  • Harvest: the most practical method of reducing yield losses is to harvest heavily infested fields as soon as possible to minimize lodging loss
  • Planting time: avoid early planting with short-season varieties in areas with known problems
  • Insecticides: often ineffective against adults (extended emergence period) and larvae (protected inside stem)
  • Plant resistance: no known resistant soybeans
  • Cropping pattern: avoid crop rotation into commercial sunflowers infested the previous year
  • Tillage: disking or burying infested soybean stems after harvest can reduce subsequent populations
Dectes stem borer distribution and percent infestation in Kansas soybeans

Dectes stem borer distribution and percent infestation in Kansas soybeans (modified from Buschman & Sloderbeck. 2010 J. Insect Science)

 
Photos and Text
Marlin E. Rice, DuPont Pioneer
Reviewed by Phil Sloderbeck (Kansas State University),
and Paula Davis and Herb Eichenseer (DuPont Pioneer)
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