Agronomy •  4/20/2022

Southwestern Corn Borer

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From Pioneer Agronomy Sciences

Key Points

  • Southwestern corn borer occurs in southern corn regions from Arizona to western Georgia and northward to south-central Kansas, southern Illinois and southern Missouri.
  • 2 to 3 generations occur each year depending on elevation and latitude.
  • Yield impact is primarily due to stalk tunneling. Kernel feeding can increase aflatoxin levels in grain.

Pest Facts

  • Common name: southwestern corn borer
  • Latin name: Diatraea grandiosella, family Crambidae
  • Description
    • Adult: dull-white or buff-colored moth; wingspan
      ¾  to 1½ inches (19 to 38 mm)
    • Larva: (summer phase) creamy white with large, raised brown or black tubercles on each body segment; (winter phase) creamy white and without distinctive spots; head black (instars 1 to 3) or reddish brown (instars 4 to 6)
    • Egg: flat and oval, laid in clusters; pale yellow-green when first laid, but within 36 hours develops three orange-red lines (see photo below)

Larvae of southwestern corn borer: winter (diapause) phase (top) and summer phase (bottom)

Photo - southwestern corn borer adult - moth

Adult Southwestern corn borer

Photo - Southwestern corn borer eggs

Southwestern corn borer eggs

Injury and Pest Symptoms

Whorl-stage corn

  • First- and second-stage larvae feed 9 to10 days in whorl, creating pinholes and small, circular lesions or “windows” to large elongated holes
  • Third-stage larvae depart the whorl, crawl down the plant, and burrow into the stalk
  • Tunneling may damage the growing point, causing “dead heart” and stunted plants
  • Large larvae tunnel vertically in the stalk
  • Tunneling reduces uptake of nutrients and water, which stunts plant height and reduces grain yield

Reproductive-stage corn

  • Early-stage larvae feed between husk leaves, on ear shoots and behind leaf sheaths
  • Late-stage larvae may feed on kernels, often near base of ear, but eventually tunnel into stalk (see photos) and tunnel may be 12 inches long

Photo - SWCB larva tunneling in corn stalk

Larva tunneling in corn stalk.

Pest Status and Importance

  • In corn, 29% yield loss reported from stalk tunneling
  • Additional harvest losses of 50 to 75% can occur during fall when larvae girdle stalks, causing corn to lodge
  • Kernel feeding can increase aflatoxin levels in grain
  • In sorghum, up to 50% yield loss may occur

Similar Species:

  • European corn borer and sugarcane borer

Life History:

  • Larvae pupate in the spring inside corn stalks at the base of plants
  • Females lay up to 400 eggs on leaves, stalks, and ear husks
  • Eggs hatch in 4 to 7 days
  • Early-stage larvae feed in corn whorls, behind leaf sheaths, or on husk leaves, ear shoots, and kernels
  • Late-stage larvae tunnel into the stalk
  • Larvae complete 5 to 6 stages; summer generation requires 38 to 56 days
  • Overwintering (diapause) larvae crawl to base of stalk, tunnel inside, and create an internal girdle
  • Larvae are cannibalistic; usually only one larva overwinters in base of stalk
  • 2 to 3 generations occur each year depending on elevation and latitude
  • Fungus, Beauveria bassiana, may kill 50% of larvaeuropean corn borer and sugarcane borer

Photo - Kernel damage and entrance hole at corn plant base from SWCB

Kernel damage and entrance hole at plant base.

Origin and Distribution

  • Native to North America, including Mexico
  • Occurs in southern corn regions from Arizona to western Georgia and northward to south-central Kansas, southern Illinois and southern Missouri
  • Larvae cannot survive in regions where the 10-year average January temperature is below 19°F

Photo - Corn stalk girdled by corn borer larva.

Corn stalk girdled by larva.

Integrated Pest Management Practices

Bt Corn Hybrids

  • Pioneer® brand products containing a corn borer trait provide excellent control; contact a Pioneer representative for trait availability

Non-Bt Corn Hybrids

  • Plant early: More mature plants are damaged less by 2nd and 3rd generation larvae
  • Scout fields: Economic threshold is 20 to 25% of plants infested with eggs or young larvae; pheromone traps can predict moth flight and time to scout; contact state extension entomologist for resource information and scouting procedures
  • Insecticides: Application of insecticide must occur before larvae tunnel into stalk; contact your state extension entomologist for recommended insecticides
  • Post-harvest crop destruction: Stalk shredding and minimum tillage that breaks the stalk at ground level reduces overwintering survival

Photos & Text: Marlin E. Rice (Corteva Agriscience); Reviewed by Scott Stewart (University of Tennessee), and Paula Davis and Herb Eichenseer (Corteva Agriscience)


The foregoing is provided for informational use only. Please contact your Pioneer sales professional for information and suggestions specific to your operation. Product performance is variable and depends on many factors such as moisture and heat stress, soil type, management practices and environmental stress as well as disease and pest pressures. Individual results may vary. Pioneer® brand products are provided subject to the terms and conditions of purchase which are part of the labeling and purchase documents.