The Online Gardener's Handbook 2010
Chapter 1: Causes of Plant Injury
Identifying Insect Injury on Plants

Identifying Insect Injury on Plants

Chewed Leaves and/or Chewed Flowers

SymptomPossible Causes
Pieces of leaf or flower missingCaterpillars, Weevil adults (on flowers)
Notched leaf bordersRoot weevil adults
Entire leaves or flowers missingLarvae or adult beetles, Sawfly larvae, Grasshoppers, Slugs/Snails

 

Damage to fruit or fruiting vegetables

SymptomPossible Causes
Depressions Plant feeding bugs
HolesFruit-feeding caterpillars, Fruit-feeding beetles, Maggots
Irregular surface (bumpy)Plant-feeding bugs
Shrivelled/misshapenAphids, Sawflies
Silvery surfaceThrips
Early fruit dropMaggots, Weevils

 

Discoloured Leaves

SymptomPossible Causes
Bleached leavesLace bugs
Bronzed leavesSpider mites, Plant bugs
Silvered leavesThrips, Mites
Stippled leavesLeafhoppers
Streaked leavesAphids, Psyllids, Thrips
Brown leaf edgesLeafhoppers

 

Parts of Plant are Distorted

SymptomPossible Causes
Mined leavesLeafmining caterpillars and maggots
Skeletonized leavesBeetle larvae or adults, Some caterpillars, Sawfly larvae
Curled/cupped leavesAphids, Leafrollers
Galls on leaves, stems, flowers, twigsThrips, Gall wasps
Twisted growing pointsGall flies, Psylids, Eriophyid mites

 

Parts of Plant Die

SymptomPossible Causes
Dying leaves, twigs, branchesTwig pruners, Shoot borers
Whole plant dyingRoot-feeding beetle larvae, Vegetable maggots, Some caterpillars, Wireworms (vegetables)
Bark splitting/tunnelling under barkBoring insects, scales (large infestations only)
WiltingRoot-feeding beetles, Root-feeding caterpillars, Aphids/Leafhoppers (large infestations only)
Poor seedling health/seedlings don't emergeWireworms, Millipedes (occasional), Maggots, Root-feeding caterpillars
Stems cut/plants falling overCutworms, Slugs/Snails

 

Damage to underground plant parts (e.g. root crops)

SymptomPossible Causes
Holes/tunnels
Scraping/channels on outer surface
Scars
White grubs
Wireworms
Millipedes (occasional)
Root-feeding maggots

 

Visible Insect Matter

SymptomPossible Causes
Dark fecal spotsLace bugs, Thrips, Plant bugs
Honeydew, Sooty mould Aphids, Soft scale insects, Mealybugs, Psyllids, Whiteflies, Leafhoppers
Silken matsLeafrollers, Leaf tiers, forest tent caterpillar
SpittleSpittlebugs
TentsTent caterpillars
WebsWebworms
Cast skins Aphids, Cicadas, Clearwing moth larvae, Lacebugs, Leafhoppers
Pitch mass Larvae of certain kinds of moths and beetles
Sap flowLarvae of certain kinds of moths and beetles
Pitch tubes Bark beetles
Cottony waxy materialAdelgids, Aphids, Certain scales, Mealybugs, Psylids
Slime Slugs/Snails
Holes and frass (fecal material)Boring insects

 

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For more information:
Toll Free: 1-877-424-1300
E-mail: ag.info.omafra@ontario.ca
Author: OMAFRA Staff
Creation Date: 03 May 2010
Last Reviewed: 24 June 2010