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What
bug did it and where did it go?
Dr. Charles R. Ward, Extension/Research
Entomologist
New Mexico State University
Diagnosing Plant Problems caused by Insects = Symptomology
Categories:
- Chewed or Tattered Foliage or Blossoms.
- Stippled, yellowed, bleached or bronzed foliage
- Distortion of Plant parts
- Dieback of plant parts.
- Presence of insect or insect-related products.
Category 1 Symptoms
Chewed or Tattered foliage or blossoms
Symptoms of an insect or insect relative with biting-chewing
mouthparts such as:
- snails and slugs
- grasshoppers
- larvae of, and sometimes adult, beetles
- larvae of moths or butterflies
- sawfly larvae
Category 2 Symptoms
Stippled, yellowed, bleached, or bronzed foliage
Symptoms of an insect or insect relative with sucking (not
biting-chewing) mouthparts such as
- spider mites
- thrips
- plant bugs
- aphids
- psyllids
- lace bugs
- leafhoppers
- whitefly
Category 3 Symptoms
Distortion of plant parts
Symptoms of an insect or insect relative with sucking (not
biting-chewing) mouth parts whose feeding and injection of salivary fluids cause
distortion of plant parts such as:
- eriophyid gall (blister, bud or rust) mites
- thrips,
- aphids
- psyllids
- cynipid (gall) wasps
Category 4 Symptoms
Dieback of plant parts
Leaf, twig or branch dieback, or in a few cases, cause death
of the entire plant, such as :
- scale insects,
- moth or beetle larvae that bore
- cynipid (gall ) wasps
Category 5 Symptoms
Presence of insect or insect-related products
The most commonly seen products, and the pests responsible for
them are:
- Honeydew and sooty mold
- Aphids, soft scales. leafhoppers,
mealybugs, psyllids, and whiteflies
- Dark fecal specks:
- Greenhouse thrips and plant bugs.
- Tents, webs, and silken mats:
- Tent caterpillars, webworms, and leaf
rollers
- Spittle:
- Spittlebugs
- Cast skins,
- Aphids, leafhoppers, and lace bugs
- Pitch masses:
- Larvae of certain moths, such as bark
and pitch moths and pinyon pitch nodule moth
- Pitch tubes:
- Certain scolytid bark beetles, such as
the Dendroctonus sp.
- Flocculence (cottony waxy material):
- Adelgids,. mealybugs, certain scales,
and aphids.
- Slime:
- Snails, slugs, and certain Hymenoptera
such as the pear or cherry slug.
Example Multiple symptom categories
Aphids
Category 2. Leaf yellowing
Category 3. Plant distortion
Category 5. Insect products:
- Honeydew, sooty mold
- Cast skins
- Flocculence
When should control action be taken?
Economic threshold:
When damage levels are greater than control
costs
($$)
Aesthetic threshold:
When damage levels are unacceptable
or intolerable (looks)
Factors affecting the aesthetic
threshold:
Location of the plant in the landscape
(visibility)
- Back yard
- Higher numbers - more damage tolerated
- Front yard
- Lower numbers - less damage tolerated
Species of pest involved
- aphids -high numbers generally
tolerated
- scales -moderate numbers tolerated
- bark beetles -use preventive measures
Whether pest is increasing or
decreasing
- increasing-more damage will occur
- decreasing-most damage already occurred
Time of year the pest appears (especially
for foliage pest)
- spring -much time for severe damage to occur
- summer -less time for severe damage to occur
- fall- little time for severe damage to occur
Time delay for strategy to be
effective
- slow - lower action threshold
- moderate - moderate action threshold
- rapid - higher action threshold
Reference:
Koehler, C.S. 1990. Insect Pest Management Guidelines for
California Landscape Ornamentals. U. California, Div. Agric, and Natural
Resources, Pub 3317, 82pp.
03/19/2006
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