Diagnosing Injury to Woody Ornamentals

Adapted from Johnson, W.T. and H.H. Lyon. 1991. Insects that feed on trees and shrubs. 2nd ed., Cornell Univ. Press, Ithaca, New York, 560 pp.
Diagnosing Injury to Woody Ornamentals - Articles


In This Article

by Gregory A. Hoover

Possible Causes of Injury to Plants

Abiotic Environment


  • Industrial wastes
  • Air pollution
  • Phytotoxicity (pesticides)
  • Salt (chemical) accumulations
  • Concrete and macadam
  • Soil compaction
  • Changes in soil level
  • Changes in groundwater level
  • Mechanical injury by auto, machinery, and vandalism


  • Mineral deficiencies
  • Frost and freeze
  • Sun scorch
  • Drought
  • Lightning
  • Wind
  • Hail
  • Blowing sand
  • Flood

Biotic Environment


  • Insects
  • Mites
  • Nematodes
  • Millipedes
  • Slugs and snails
  • Birds (woodpeckers)
  • Rabbits, mice, moles and other rodents
  • Dogs
  • Humans


  • Viruses
  • Phytoplasmas
  • Bacteria
  • Rickettsialike organisms
  • Fungi
  • Dodder
  • Mistletoe
  • Algae
  • Moss
  • Weeds
  • Strangling vines
  • Strangling roots

Symptoms of Insect Attack

Chewed foliage or blossoms

  • Larvae of moths and butterflies
  • Sawfly larvae
  • Beetle larvae or adults
  • Tree crickets, grasshoppers, and walkingsticks
  • Snails and slugs

Bleached, bronzed, silvered, stippled, streaked or mined foliage

  • Leafhoppers
  • Aphids
  • Lace bugs
  • Psyllids
  • Plant bugs
  • Spider mites
  • Thrips
  • Leafminers

Distortion (swelling, twisting, or cupping of plant parts)

  • Thrips
  • Aphids
  • Eriophyid mites
  • Gall makers
  • Psyllids

Dieback of twigs, shoots, or entire plant; sometimes with holes in bark

  • Wood borers
  • Bark beetles
  • Scale insects
  • Gall makers
  • Root-feeding beetle larvae

Signs - Presence of the Insect or Insect-related Products on Plants

Honeydew and subsequent sooty mold

  • Aphids
  • Mealybugs
  • Soft scales
  • Psyllids
  • Leafhoppers
  • Whiteflies

Fecal specks on leaves

  • Lace bugs
  • Greenhouse thrips
  • Some leaf beetles
  • Some plant bugs
  • Some sawfly larvae

Tents, webs, and silken mats

  • Tent caterpillars
  • Leaftiers
  • Webworms

Bags and Cases

  • Bagworms
  • Casebearers


  • Spittlebugs

Cottony fibrous materials

  • Adelgids
  • Some scales
  • Mealybugs
  • Some whiteflies
  • Some aphids
  • Flatids


  • Snails
  • Slugs

Pitch tubes

  • Some bark beetles

Pitch or gum masses and sap flow

  • Larvae of some moths
  • Larvae of some beetles
  • Larvae of some midges

Some Selected References in Entomology

General Entomology

Arnett, R. H., Jr. 1985. American Insects, a Handbook of the Insects of America North of Mexico. New York, Van Nostrand Reinhold Co., xiii + 850 pp. ; illus.

Borror, D. J., C. A. Triplehorn, and N. F. Johnson. 1989. An Introduction to the Study of Insects. 6th edition, Philadelphia, Saunders College Publishing, xiv + 875 pp.

Borror, D. J.,and R. E. White. 1970 (paperback ed., 1974). A Field Guide to the Insects of America North of Mexico. Boston: Houghton Mifflin, 404 pp.; illus.

Comstock, J. H. 1949 (9th ed.). An Introduction to Entomology. Ithaca, N. Y.: Comstock, 1064 pp. ; illus.
Jacques, H. E. 1947 (2nd ed.). How to Know the Insects. Dubuque, Iowa: Wm. C. Brown, 205 pp.; illus.

Stehr, F. (Ed.). 1987 and 1991. Immature Insects. Vols. 1 and 2, Dubuque, Iowa: Kendall/Hunt, 754 pp. and
975 pp.; illus.

Torre-Bueno, J. R. 1978. A Glossary of Entomology. N.Y. Entomol. Soc., New York, 336 pp.

Landscape Entomology

Dreistadt, S. H., J. K. Clark, and M. L. Flint. 1994. Pests of landscape trees and shrubs: an integrated pest management guide. Univ. Calif., Div. Agric. and Nat. Res., Publ. 3359, 327 pp.

Drooz, A. T. (ed.) 1985. Insects of eastern forests. USDA, Forest Serv., Misc. Publ. 1426, 608 pp.

Hoover, G. A. 2000. Insects and mites, In Woody Ornamental Insect, Mite, and Disease Pest Management, W. K. Hock, G. A. Hoover, and G. W. Moorman, Pennsylvania State Univ., College of Agricultural Sciences, 86 pp.

Ives, W. G. H. and H. R. Wong. 1988. Tree and shrub insects of the prairie provinces. Information Report NOR-X-292, Northern Forestry Centre, Canadian Forestry Service, Edmonton, Alberta, xi + 327 pp.

Johnson, W. T. and H. H. Lyon. 1991. Insects that feed on trees and shrubs. 2nd ed. rev., Cornell Univ. Press, Ithaca, New York, 560 pp.

Koehler, C. S. 1987. Insect pest management guidelines for California landscape ornamentals. Coop. Ext. Univ. Calif., Div. Agric. and Nat. Res., Publ. 3317, 82 pp.

Orton, D. A. 1989. Coincide: the Orton system of pest management. Plantsmen's Publications, Flossmoor, IL., 190 pp.

Pirone, P. P. 1978. Diseases and pests of ornamental plants. 5th ed., John Wiley & Sons, New York,
x + 566 pp.

Wilson, M. C., D. L. Schuder, and A. V. Provonsha. 1982. 2nd ed., Practical insect pest management, 4. Insects of ornamental plants., Waveland Press, Inc., Prospect Heights, IL, 157 pp.