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PP318 Forest Pathology Disease Profiles

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Symptoms and Signs of Plant Disease
decayed wood
leaf spot
chlorotic and necroitc leafspots

Symptoms of Plant Disease
leaf spots
wood decay

necrosis (death) of entire tree
Plant mortality (death) of 
an entire plant such as 
this dogwood.

necrosis of needles
leafspots on river birch
necrotic areas on green ash
Necrosis can also occur on plant parts such as needles (left) or parts of plants like the leafspots
on river birch (middle) or the necrotic areas on leaflets of green ash (right).

necrotic lesions on root
Discrete or localized 
necrotic area, such as those seen on this root.

 The localized death of woody 
plant tissue usually resulting in
a collapsing of the bark and 
cambial region.
canker on black walnut

canker on black walnut
Cankers can be formed from callus tissue, seen as concentric ridges on 
the black walnut (above), which is often formed by the plant in an attempt to 
limit spread of the pathogen. In some instances the plant does not have the ability to form callus tissue as seen 
on the redbud to the right.
sunken canker on redbud

brown areas in sycamore cross-section
Vascular discoloration
Browning or darkening, seen in the cross-sections of this 
sycamore, that is indicative of dead cells.

rapid necrosis
Rapid necrosis of a plant or plant parts as seen in this slide of pear. 
The blackened leaves and twigs developed in a relatively short 
period of time (several days to a few weeks).

necrosis proceeds toward the trunk on this oak
dieback in pine tree
closeup of dieback in pine shoots
Necrosis of terminal portions of the crown and proceeding toward the trunk 
as seen on this oak (left). In some instances such as the pine (center and 
right), only the terminal dies back.

inadequate water supply or transport leads to wilting, then necrosis
Necrosis of plant cells involved in water transport, thus depriving
foliage of adequate water  and causing loss of turgor pressure.

river birch display chlorotic symptoms note chlorosis of leaves
 Necrosis of plant chloroplasts resulting in a yellow appearance as seen 
on the foliage of the river birch near D.H. Hill Library. Note that there is 
a second symptom on the chlorotic birch leaves.

chlorosis and stunting of pine needles
Chlorosis on pine needles.

decayed wood
extensive heartrot in a tree trunk
Wood decay involves disintegration of dead woody plant cells and is technically not a disease. However, since decay destroys the most valuable part of a tree (wood), it is discussed in some detail in this course.

Atrophy (Hypoplasia)
stunted pine seedlings

note the size difference of these white pines reduced size of cones
Atrophy or hypoplasia involves the slowing down or retardation of normal plant 
processes resulting in a stunting of the entire plant or plant parts. Note the size 
difference and the shoot and needle growth difference in the pines (left)
(chlorosis is also evident) and the size of the cones (right).

note the chlorotic areas around the leaf spots
Chlorosis also can result from the inhibition or retardation of chloroplast function and 
development. This condition also can be noted on the white pine in the previous
slide. Note the yellow (chlorotic) areas around the leafspot on this river birch.

Hypertrophy and Hyperplasia
witch's broom
witch's broom

Abnormal increase in cell size.
Abnormal increase in cell numbers.

These conditions frequently occur together and cannot be distinguished without a microscope. Both conditions, separately and together, can cause overgrowths of a plant part or an area on a plant.

gall on tree trunk
multiple galls on tree trunk
gall on tree trunk
Terms used to describe this  symptom: Gall or Burl

blistering of foliage
Note the chlorosis on the blisters.

witches broom high in tree
witch's broom
very large, dense witches broom1
Witch's broom

Signs of Plant Disease
basidiocarps (mushrooms in this case)
Signs are any physical or direct evidence of a disease-causing agent discernable with
the unaided eye. This limits signs chiefly to those agents such as some fungi, nematodes
and parasitic plants that produce macroscopic structures. This photo on the right shows
mycelium and mycelial strands growing from a diseased root.

black mycelium
Black mycelium growing on needles and twigs of white pine.

mycelial fan growing under bark
Mycelial fan (the grey area at the base) growing under the bark of an infected yellow birch.

closeup of sclerotia
These small round structures are sclerotia of a fungal pathogen and are frequently produced by certain fungi.


Black shoe-string like structures are rhizomorphs.

mushrooms (a kind of basidiocarp)
Most signs of fungal pathogens are reproductive structures such as these basidiocarps (mushrooms) growing from
the base of an oak.

conks of a shelf fungus (a type of basidiocarp)
small, numerous shelf fungus basidiocarps
Basidiocarps (conks or brackets) of a wood decay fungus on a
southern red oak (left) and an oak branch (above).

Apothecia (reproductive structures of a certain class of fungi) growing on a 
larch twig.

Spore masses of a fungus growing on a dogwood leaf.
closeup of spore masses

perithecia on an elm leaf closeup of perithecia on black walnut
Perithecia (reproductive structures of a another class of fungi) growing on 
an elm leaf; red perithecia on a canker on a black walnut tree.

bright orange, gelatinous telial horns
Spore horns of a fungus that 
attacks red cedar.
spore tendrils
Spore tendrils of a fungus
growing on red cedar needles.

note yellow-orange aecia on this gall
Yellow-orange blister-like spore-bearing structures termed aecia of a fungus on pine.

tiny shoots of dwarf mistletoe growing from parasitized pine
The yellowish structures growing on this ponderosa pine are shoots of a
dwarf mistletoe plant that
is parasitizing the pine.

leafy mistletoe
The greenish-yellow structures growing on this oak are shoots of 
the parasitic higher plant true mistletoe or leafy mistletoe.

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This website was prepared by Becky Bernard.
Last updated 04 February 2008 by M.J. Munster