Sweetpotato Root Damage Guide'ppt

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Sweetpotato Insect Pest Identification Guide Root
Feeders - Soil Insects
Dr. Kenneth A. Sorensen Extension Entomologist
N.C. State University N.C. Cooperative Extension
Service
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Sweetpotatoes damaged by insects OFTEN CAN NOT
IDENTIFY TO SPECIES
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Soil Insect Complex

• Sweetpotato Weevil
• Wireworms - 3 species
• White grubs - 4 species
• White-fringed beetle
• Sweetpotato flea beetle
• Systena and Diabrotica
• Others
• WDS Label Damage

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Table of Contents

• Introduction..1
• Some helpful steps to discern causal
  insect..2Key to the Soil
  Insects on Sweetpotato Roots in the United
  States.3
• Sweetpotato leaf beetle, Typophorus nigritus
  viridicyaneus (Crotch)....4
• Sweetpotato weevil, Cylas formicarius
  elegantulus (Summers)5
• Sweetpotato flea beetle, Chaetocnema confinis
  Crotch..6
• Whitefringed beetle, Graphognathus
  spp....7Banded cucumber
  beetle, Diabrotica balteata LeConte...8
  Elongate flea beetle, Systena elongata
  (Fabricius)9Corn earworm,
  Helicoverpa zea (Boddie)....10
  Variegated cutworm, Peridroma saucia
  (Hübner)..11
• White grubs......12
• Japanese beetle, Popillia japonica
  Newman, Spring rose beetle,
  Strigoderma arboricola Fabricius, Phyllophaga
• Green June Beetle, Cotinis nitida
  (Linnaeus).13
• Sugar Cane Beetle, Euetheola humilis rugiceps
  (LeCont) 14
• Wireworms......15-17
• Southern potato wireworm, Conoderus
  falli (Lane)
• Corn wireworm, Melanotus communis
  Gyllenhal
• Tobacco wireworm, Conoderus
  vespertinus (Fabricius)

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Introduction

• Some 20 species of insects feed on edible
  sweetpotato roots. Insect feeding lowers the
  quality of sweetpotatoes, Ipomoea batatas, by
  marring their appearance, providing entry sites
  for decay organisms, causing waste when the roots
  are cooked, and sometimes by causing
  objectionable tastes. Growers are unaware of
  insects until harvest, when they discover damage.
  Several insects produce characteristic scars that
  can be accurately identified. Some injury can be
  diagnosed with experience and background
  information. However, injury by many insect
  species is so similar in appearance that a
  positive and accurate identification cannot be
  made. Recent feeding injury is easier to
  identify than old injury that has been altered by
  root growth, soil rots, or secondary insect
  attack. Depth of insect holes varies with
  insect species but this relative depth of the
  holes can be drastically altered by growth of the
  root. Early season feeding scars that do not
  penetrate the cortex flatten out. A scar that
  penetrates the cortex becomes deeper through root
  growth. Varieties with a thin or thick cortex
  may express damage differently. Also different
  varieties of sweetpotatoes or the same variety
  grown in different soil types, moisture
  conditions etc. may have different insect damage.

SCIENCE ART REQUIRES DETECTIVE APPROACH
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Some helpful steps to discern causal insect
follow

• 1. Examine roots at frequent intervals during
  the growing season.
• 2. Search for insect stages in the soil.
• 3. Collect adult insects in the field.
• 4. Recognize insect feeding injury to the
  foliage.
• 5. Use corn seed soil baits.
• 6. Use sex pheromone traps.
• 7. Use water pail traps.
• 8. Use light traps.
• 9. Use sweep nets.
• 10. Use bug vacuums.
• 11. Use yellow sticky traps.
• 12. Keep records of insects and root damage.
• 13. Other associated factors

MUST LOOK AT FOREST TREES ROOTS
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Dichotomous and Pictorial Key to the Soil
Insects On Sweetpotato Roots in the United States
1 Sweetpotato roots with some surface
feeding but mostly interior feeding damage 2  
2 Sweetpotato roots with mostly shallow and
some deep surface feeding damage 3   2a Some
vine tunnels but mostly have excrement filled
tunnels deep into the roots. Eg.
Sweetpotato leaf beetle   2b Small holes
(wooden matchsticks) on the surface of the roots
and enlarge as damage extends inwards.
Some tunnels with insect stages present
Eg. Sweetpotato weevil 3a Small, narrow
winding channels on roots. Adults do similar
damage on foliage. Eg Sweetpotato flea
beetle. 3b No small, narrow winding channels
on roots. 4 4a Large, irregular channels
or cavities on roots. Eg. Whitefringed beetle
4b No large, irregular channels but usually
several holes on roots. 5 5a
Sweetpotato roots with some surface feeding
damage but mostly with many deep holes 9
5b Sweetpotato roots with mostly surface
feeding damage 6a or usually one or two
deep holes 6b 6a Small, round
holes clumped on surface of roots and sometimes
with irregular shaped enlarged cavities
underneath skin. Eg .Diabrotica Cucumber beetle
Banded and spotted 6b No small,
round holes clumped on surface of roots and no
irregular shaped enlarged cavities
underneath the skin 7 7a Small, pinhole
late season injury or healed hole early season
injury. Eg. Systena Flea beetle 7b
No small pinhole late season injury or healed
hole early season injury 8 8a Large deep
holes singly on the root surface Eg. Corn
earworm 8b Top of the root stem end. Eg
Cutworms 9a Large rough holes usually
grouped on the bottom side of the roots. Some
shallow but mostly deep holes. Eg.
White grub Phyllophaga species Green June, May,
False Japanese, Japanese and Sugar Cane
Beetles 9b Ragged holes randomly over the
roots. Early feeding is shallow with large
cavities late or most recent feeding
appears as ragged deep holes. Feeding frass may
be present in holes the size of a lead
pencil. Some species make cavities deep into the
root. Eg. Wireworms Tobacco, Southern
potato and corn wireworms---others
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Sweetpotato Flea Beetle Chaetocnema confinis
Crotch
The larvae make small winding tunnels just under
the skin of sweetpotato roots. These tunnels are
nearly invisible at first but soon darken and can
be seen through the skin.
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Whitefringed Beetle Graphognathus spp.
Larvae and damage to root
Whitefringed beetle larvae are particularly
destructive to taproots and underground stems.
Damage consists of rough holes and surface
channels with rough ridges.
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Banded Cucumber Beetle Diabrotica balteata LeConte
Cucumber beetle larvae eat small round holes
through the skin of sweetpotato roots, and form
irregularly-shaped enlarged cavities just under
the skin.
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Elongate Flea BeetleSystena elongata (Fabricius)
Healed-hole injury resulting from earlyseason
feeding by elongate flea beetle.
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Pinhole injury resulting from late-season feeding
by elongate flea beetle.
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White Grubs
White grubs are larvae of June and May beetles.
Sweetpotatoes injured by grubs have large but
shallow feeding scars over their surface. Their
injury is unlike that of any other insect except
cutworms, but grub scars are much rougher and
frequently shallower. They feed on most
underground plant parts. In certain cases they
have been known to strip the taproot bare. Since
grubs feed upside down in the soil, horizontal
roots are injured mostly on the under side.
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Corn wireworm Melanotus communis Gyllenhal
Southern Potato Wireworm Conoderus falli (Lane)
Southern potato wireworm (A) adult (B) larva (C),
tip of larval abdomen
Southern potato wireworm adult
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Tobacco WirewormConoderus vespertinus (Fabricius)
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Wireworm
Wireworms chew ragged holes on roots. Early
feeding appears as shallow large cavities. Late
or most recent feeding appears as ragged, deep
holes.
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Wireworm
Wireworm in sweetpotato
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Wireworm
Southern potato wireworm feeding scars. Note
ragged edges and chewed fiber in holes. This
wireworm usually attacks sweetpotatoes late in
the season. (above right )
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Sweetpotato pests typically monitored by
different types of insect traps
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Sweetpotato root feeders and their damage
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Additional causes of damage to sweetpotatoes

• soil pathogens
• herbicide injury
• cold injury
• flooding/sour rot
• genetic mutations
• nutgrass injury

• decay organisms on
• lateral root scars
• rodents
• deer
• enlarged lenticils
• nematodes

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Traps in the Field
Corn Wireworm Stages Larva, pupa, adult
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• Management Practices
• Diseases, insects "regulated pests" threaten
  efficient sweetpotato
• productionand marketing by lowering yield,
  reducing quality, and
• restricting sales. These risks are minimized by
  using integrated pest
• and crop management systems.
• Select loamy, fertile, well-drained fields free
  of hardpans, harmful residues,
• troublesome weeds. Sample soil annually for
  pH, nutrients, nematodes,
• soil insects.
• Use a minimum two-year crop rotation. Avoid
  fields previously in sod or fallow.
• Select commercially acceptable varieties with
  some resistance to insects,
• nematodes and diseases.
• Use only planting stock produced in areas free
  of sweetpotato weevil
• other pests. All purchased plants
  originated off-farm must be certified

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THANK YOU for your attention, cooperation,
and continued interest . Best Wishes for 2006!