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White Grub

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Symptoms of White Grub in Corn

  • Young plants are stressed and turn light tan, yellow, or purple from nutrient and moisture stress
  • Plants wilt, grow slowly and may die, reducing stands
  • Plants that survive are usually behind in development compared to surrounding plants

Young corn plants showing white grub symptoms. Young plants are stressed and turn light tan, yellow, or purple from nutrient and moisture stress.

Corn field showing white grub damage. Plants that survive are usually behind in development compared to surrounding plants.

Pest ID / Similar Species

  • True white grub identified by two parallel rows (zipper) of hairs on raster (underside of tail). (photo and drawing below)

True white grub identified by two parallel rows (zipper) of hairs on raster (underside of tail).
True white grub or May/June beetle (3-year grub)
True white grub or May/June beetle (3-year grub)

  • Annual white grubs = Cyclocepha lalurida (drawing below)
    • Annual white grub identified by lack of parallel rows of hairs on their raster; the hairs are randomly scattered
    • Annual white grub feeds on organic matter in soil

Annual white grub or Masked chafer (1-year grub.)
Annual white grub or Masked chafer (1-year grub)

  • Japanese Beetle = Popillia japonica (drawing below)
    • Japanese beetle rasters form a prominent "V"

Japanese beetle (1-year grub.)
Japanese beetle (1-year grub)

  • Manure grubs = Aphodius spp (photo below)
    • Manure grubs are very small and feed on decaying organic matter in the soil

Green June Beetle grubs.

  • Green June Beetle =Cotinis nitida
    • Green June Beetle grubs can be up to 2 inches long and if given the chance will crawl away on their back

Facts and Impact on Crop

  • White Grubs of the Phyllophaga genus (called "True" White Grubs) are the only ones found to cause stand losses in corn as they may be present the complete season and generations may overlap
  • Damage only occurs on the young corn seedling
  • Significant damage can occur from true white grub densities of one larva per cubic foot prior to planting
  • There is little loss from annual white grubs as they feed for a short period only
  • A C-shaped grub up to 1 ¼ inches long

True White Grub larvae.

Life Cycle of White Grub in Corn

True White Grub 3-year life cycle. 2 species or generations may overlap within the same field.

Hosts and Distribution

Hosts

  • Research in North Dakota found primary distribution of Phyllophaga grubs within 100 feet of shelterbelts consisting of cottonwood, willow or similar species near row crop fields
  • Ovipositon and natural habitat are in wooded or grassy areas, and different species probably have different specific host plants
  • Corn and other row crops are incidental hosts of larval white grubs

Photo - Research in North Dakota found primary distribution of Phyllophaga grubs within 100 feet of shelterbelts consisting of cottonwood, willow or similar species near row crop fields.

Distribution

  • Although most states in the United States have at least one species, most species of Phyllophaga are found east of the Rocky Mountains
  • There are more than 25 species present in the Midwest, Northeast and South

Photo - corn field damage from white grub - most species of Phyllophaga are found east of the Rocky Mountains.

Management Considerations

Scout fields by watching soils for white grubs during spring tillage

  • An infestation may be quite localized where vegetation and soil moisture were conducive to egg laying and grub survival
  • A pesticide at planting may be warranted if there are signs of white grubs prior to planting
    • Soil samples (>2/Cu ft); Previous history
  • Insecticides applied at planting or high rate of insecticide seed treatment may give some protection
  • Rescue insecticides after the crop has been planted are not effective, replanting is the only remedial treatment
  • No transgenic products control white grubs
  • In localized areas of stand loss or reduced growth, replanting may be warranted
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