Insect Pests of Alfalfa and Corn

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Insect Pests of Alfalfa and Corn

• Southeast Idaho Forage School
• March 16, 2006
• Kelly V. Tindall
• Extension Entomologist,
• Twin Falls County

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Wireworms

• Description cylindrical, light tan to reddish
  tan larvae, usually hard bodied
• Biology prefer porous, well drained loam soils
  injury more severe when corn follows pastures,
  small grains and other forage crops

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Wireworm Injury

• Feed on seeds before or during germination
• Reduced stands and vigor
• Bore in to seedlings below soil surface
• Plants wilt and turn yellow

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Baits for Wireworms

• Hole aprx. 4 X 10 inches 1-3 wk before planting
• Place in grassy areas or areas of previous
  infestations

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Baits for Wireworms

• Hole aprx. 4 X 10 inches 1-3 wk before planting
• Place in grassy areas or areas of previous
  infestations
• ½ cup of mixture of non-treated wheat and corn
  seed, soak seed in water for 24h

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Baits for Wireworms

• Hole aprx. 4 X 10 inches 1-3 wk before planting
• Place in grassy areas or areas of previous
  infestations
• ½ cup of mixture of non-treated wheat and corn
  seed, soak seed in water for 24h
• Fill remainder of hole with soil and mound

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Baits for Wireworms

• Hole aprx. 4 X 10 inches 1-3 wk before planting
• Place in grassy areas or areas of previous
  infestations
• ½ cup of mixture of non-treated wheat and corn
  seed, soak seed in water for 24h
• Fill remainder of hole with soil and mound
• Cover with a 3ft black plastic square, put soil
  on top to prevent wind removal (? soil temp and
  germination)

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Baits for Wireworms

• Hole aprx. 4 X 10 inches 1-3 wk before planting
• Place in grassy areas or areas of previous
  infestations
• ½ cup of mixture of non-treated wheat and corn
  seed, soak seed in water for 24h
• Fill remainder of hole with soil and mound
• Cover with a 3ft black plastic square, put soil
  on top to prevent wind removal (? soil temp and
  germination)
• Minimum of 5-10 bait stations per 25-30 acre
  field
• Check 2-3 days prior to planting 1 per bait
  economic infestation

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Summary of Wireworm Trials Increase in Stand
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Summary of Wireworm Trials Reduction in Damage
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Corn Rootworms
Rootworms are worse in corn-corn rotations 90
of corn treated when not rotated vs 25 when
rotated
http//lamar.colostate.edu/gec/vg.htm
Marlin Rice
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Southern Corn Rootworm

• AKA spotted cucumber beetle (adult)
• Larva cream colored body, brown head, up to ¾
  in, 6 short legs, projections on the anal plate
  on the last abdominal segment
• Adult ¼ in, yellow-green body, black head, 12
  spots on wings
• Overwinters as adult
• Minor pest, except TX LA

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Western Corn Rootworm

• Larva creamy white body, up to ½ in., dark brown
  head and anal plate on last abdominal segment
• Adults light yellow to light green, 3 black
  stripes on wings (size of stripes vary)
• Corn is the only known crop host therefore,
  rotations have been effective in control
• HOWEVER, evidence suggests 2 biotypes one that
  lays eggs only on corn and one that will lay on
  soybeans making corn/soybean rotations
  ineffective

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Summary of CRW Trials Reduction of Injury
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Alfalfa Weevil
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Alfalfa Weevil
Adults - dark gray about 0.20 inch long
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Alfalfa Weevil
Adults emerge from overwintering sites and begin
laying eggs in alfalfa stems
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Alfalfa Weevil
Larvae hatch and make their way up the stem to
feed on alfalfa terminals
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Alfalfa Weevil
Larvae - pale green with a thin white line down
the center of the back and a brown head (¼ in).
In larval stage for 3-4 weeks.
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Alfalfa Weevil
Early summer, larvae spin cocoons on leaves or on
the ground.
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Alfalfa Weevil
Adults emerge and feed before moving to
overwintering sites.
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Alfalfa Weevil Damage

• Young larvae - feed on terminal buds
• Larger larvae most damaging stage skeletonize
  leaves and giving them a bronzy appearance in
  spring and early summer
• Severe pressure may result in complete
  defoliation
• Damage usually limited to 1st cutting -
  occasionally to 2nd or 3rd cuttings
• Monitoring once larvae seen check fields at
  every 2-4 days

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Alfalfa Weevil Thresholds

• 30 of terminals show feeding damage
• cut and treat stubble, OR
• treat the standing crop depending on how close to
  cutting it is
• ?1 week before cutting -damage is noticeable AND
  more than 10 larvae per sweep (90 sweep,
  straight-line sweep)
• 20 or more larvae per sweep (180 sweep,
  half-circle)
• General recommendations Weather conditions,
  plant vigor, irrigation, etc. can impact decisions

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Summary of Alfalfa Weevil Trials Reduction of
AW Densities
Summary of AMTs vols. 24-30
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Summary of Alfalfa Weevil Trials Reduction of
AW Densities
Summary of AMTs vols. 24-30
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Summary of Alfalfa Weevil Trials Reduction of
AW Densities
Summary of AMTs vols. 24-30
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Aphids

• Feed by sucking plant juices from the leaves,
  stems, and pods
• Injects toxins when feed
• Stunts growth
• Reduces yield
• Kills plants
• Reduces feed value
• Honeydew reduces palatably for livestock

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Aphids

• Pea Aphid
• Prefer stems to leaves
• Generally distributed on the plant
• Narrow dark bands at the tip of each segment

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Aphids

• Blue alfalfa aphid
• Bluish-green color with uniformly dark antennas
• Prefers to feed on terminal leaves or new
  re-growth
• Prefers mild temperatures, peaks in late winter
  or early spring

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Aphids

• Spotted alfalfa aphid
• Small, pale yellow or grayish, with conspicuous
  dark spots
• Occurs on lower portions of the plant
• Toxin injected when feeding
• Seedling death, stunting and yellowing of mature
  plants
• Leaf veins may turn yellow from toxin

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CO CA Thresholds
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PNW Thresholds

• Seedlings
• SAA 1-3/stem increasing
• Plants are less than 1 ft
• PA 100/sweep
• BAA less than PA
• SAA 10/stem honeydew
• Field is 2 weeks from cutting, or under water
  stress (wilting plants)
• Predators and parasites are not effective

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Summary of Aphid Trials Changes in Aphid
Densities
Summary of AMTs vols. 24-30
Increase
Reduction
Must.Max
Baythroid
Dimetho.
Warrior
Furadan
Ambush
Lannate
Lorsban
Pounce
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Summary of Aphid Trials Chances in Aphid
Densities
Summary of AMTs vols. 24-30
Increase
Reduction
Must.Max
Baythroid
Dimetho.
Furadan
Warrior
Ambush
Lannate
Lorsban
Pounce
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Summary of Aphid Trials Chances in Aphid
Densities
Summary of AMTs vols. 24-30
Increase
Reduction
Must.Max
Baythroid
Dimetho.
Warrior
Furadan
Ambush
Lannate
Lorsban
Pounce
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Summary of Aphid Trials Chances in Aphid
Densities
Summary of AMTs vols. 24-30
Increase
Reduction
Must.Max
Baythroid
Dimetho.
Warrior
Furadan
Ambush
Lannate
Lorsban
Pounce
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Stem Nematode

• Penetrates buds causing stems to enlarge and
  discolored
• Shortened internodes
• Severe infection stems may blacken up to 30 cm
  above ground
• Reduce number of stems per and eventually the
  plant dies
• May have white, slightly smaller leaves
• White flagging

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Stem Nematode

• How it spreads
• Overwinters in crown tissue and young stems
  covered by snow
• Can be spread by
• Infested seed
• Harvesting equipment
• Irrigation water

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Stem Nematode

• Control
• Resistant varieties
• 2-3 year crop rotation with non-legume crops
  (cereals)
• Field can quickly be recontaminated
• moving with machinery, animals or waste water
• Control volunteers during the rotation
• Limit the life of an infested stand to 4 years
• Clean equipment before moving from infested to
  clean fields

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