Southwestern Corn Borer | Pioneer® Seeds
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)

 



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