This document provides an overview of plant disease diagnosis and tree disorders. It discusses the importance of distinguishing between biotic and abiotic disorders, outlines the systematic diagnostic process, and describes common symptoms and signs. Key terms are defined throughout. Abiotic disorders can include improper planting sites, weather damage, and other environmental stresses. Biotic disorders involve living organisms like insects, diseases, and pathogens. Correct diagnosis requires examining multiple aspects of the plant and site conditions.

1. Ann Koenig, Urban Forester
Missouri Department of Conservation
Ann.Koenig@mdc.mo.gov
573-882-8388 x 227

2.  Distinguish between plant problems
caused by living and nonliving disorders.
 Understand the principles of a
systematic approach to the plant
diagnostic process.
 Learn to recognize the signs and
symptoms of tree disorders.
 Become familiar with various types of
insect and disease problems and their
impact on trees.

3. The Key Terms as listed in
the Arborist’s
Certification Study
Guide will be defined
and highlighted
throughout the
presentation.

4.  Trees don’t talk!
 Asking all the
necessary questions
 History is hard (or
impossible) to come
by and answers may
not be accurate.
 Most of the time –
it’s too late

5.  Symptom: how a tree
responds to a disorder
 Often times not
specific to the disorder
 Several at same time
 Examples
 Wilting
 Chlorosis (yellowing)
 Scorch
 Dieback
 Witch’s broom
 Stunted growth

6.  Sign: direct indication of the cause of the
problem, in other words something actually left
behind to whatever is causing the tree harm.
 Insect holes
 Fungal fruiting bodies

7. 1. Accurately identify the plant.
2. Look for a pattern of abnormality.
 Multiple kinds of trees-abiotic
3. Carefully examine the site.
 Drainage, construction, herbicide use,
4. Note the color, size and thickness of the
foliage.
5. Check the trunk and branches.
6. Examine the roots and root color.

13.  Time of year can help:
 Fall webworm
 Wilting oaks in summer
 Certain species are vulnerable to specific problems
 Oaks: oak wilt
 Maples: girdling roots
 Redbuds: herbicide sensitivity
 80 % of tree problems come from adverse conditions
such as:
 Soil compaction
 Mechanical injury
 Poor species selection

14.  Can be cumulative and
lead to “spiral of
decline”
 Necessary basic
factors: sufficient
water, air
movement, drainage, o
ptimal temperature
and light, and proper
balance of nutrients

15.  Short term
 Causes immediate
damage
 More likely to recover?
 Acute – disorder or
disease that occurs
suddenly or over a
short period of time
 Examples
 Lightning, herbicide, late
frost

16.  Disorder or disease
occurring over a long
period of time
 Examples:
 Poor drainage
 Soil compaction
 Poor species selection

17.  Reduced
growth
 Abnormal
foliage color or
size
 Vigorous
watersprouts
 Premature leaf
drop

18.  Not Right tree, right
place!
 H 2O
 extreme cold or heat
 soil compaction
 soil pH
 mechanical damage

19.  Biotic – pertaining to a living organism; pathogens
(microscopic disease organisms) e.g.
fungi, bacteria, viruses and nematodes [microscopic
roundworm] as well as insect pests, mites, and other
animals; a.k.a. infectious as they can spread from
one plant to the next.
 Abiotic – non living; a.k.a. non-infectious and
include environmental problems such temperature
and moisture extremes, mechanical and chemical
injuries, mineral deficiencies and many others

20.  Often the primary stress factor(s) that cause
the spiral of decline
 Can be difficult to recognize – often mimic
biotic disorders and are part of a complex
 Tree and site history often give the best clues

21.  Soil and site problems
 Right tree/right place helps
tons!
 Physical injuries
 Prevention more helpful than
treatment
 Weather:
 Frost , ice, hail wind damage
 Lightning
 Frost cracks
 Sun scald on south side of
trunk. Thin barked, young trees
with no shade
 Heat stress
 De-icing salts

22.  Competition
 shade
 turf
 allelopathy
▪ Black walnut
▪ Sugar maple
▪ Black locust
 Pollution damage
 Difficult to
diagnose, often
seen in foliage
and mimics
nutrient
deficiency

23.  Chemical injury
 2, 4 D
 From drift, movement through soil, root grafting
 Leaves cup and curl, shoots twist
 Chlorotic, browning
 Most of the time, plants recover

24.  Water availability
 Girdling roots
 Often not detected until symptoms in above ground portion.
 Prevention is best. Plant at correct depth.
 Can be possible to remove girding root

25.  Insects and Other Pests
 Disease
 Fungus
 bacteria

28.  may or may not be host
specific
 Japanese beetle vs. emerald
ash borer
 May prey on harmful
insects
 have complex life cycles
that may have both harmful
and innocuous stages
 Either feeding or egg laying
damage

29.  May feed on entire leaf
 May feed on leaf margins
 May skeletonize [leaves that have had the tissue
removed from between the veins by inects] Japanese
beetle
 Leaf mining inside leaf
 May bore through wood
 EAB in inner bark
 Asian Longhorn Beetle in wood itself

34.  Some pierce plant
cells and feed on the
contents
 Aphids
 Scales, can go
undetected
 Usually don’t kill
trees outright, but
cause stress
 Honeydew=Liquid
poo! Substrate for
sooty mold

37.  Galls are a plant
response – not a
cocoon

38. Can also be vectors, organism that transmits a
pathogen [causal agent of a disease]

39.  Mite: very small, spider
like, can cause galls
 Nematodes:
Microscopic
roundworms most of
which are not parasites
of plants
 Scotch’s pine is an
example
 May enter tree through
roots, wounds

40.  Sapsuckers
 Deer, bud feeding
 Squirrel, bark stripping
 Rabbits in winter

41.  Four requirements are
necessary for a pathogen to
infect
 Most pathogens are host
specific
 Some need alternate host
 The afflicted plant part will
give an indication of the
severity of disease
 Foliage, not so bad but noticeable
 Vascular tissue, not so good

44.  Most plant
diseases are
caused by fungi.
 Not all are bad!
Mycorrhizae=
beneficial
relationship
between roots
and fungus.
 Look for fruiting
bodies

46. Anthracnose-
leaf fungus
white or grayish fungal
growth on the surface
of stems or foliage

47.  Bacterial leaf scorch
 Fire blight on pears,
kills young tissue
 Infected plant tissues
may appear water
soaked and have a foul
odor
 Bacterial wetwood

48.  Extension
 MDC
 Missouri Community Forestry Council
 Sample:
 fresh,
 cool,
 interface between diseased and healthy tissue,
 early in week,
 good written description of problem and site