I N I NTRODUCTION TO P LANT
D ISEASES , PART II-F UNGI &
B ACTERIA
F UNGI
 Fungi are composed Fungi are composed
of living filaments called hyphae
 Need an outside food source
 Pathogens of plants and animals, sometimes  300,000 species of ffungi described; id
ib d
most are not plant pathogens
T HE H UMONGOUS F UNGUS
A RMILLARIA GALLICA
In 1992, ,
Armillaria gallica, a fungus found near Crystal Falls, MI covered 37
MI covered 37 acres, was estimated to weigh 10 tons and age was estimated at 1,500 yrs old. You may have seen
may have seen this graphic on Uhaul trucks. Since then larger, older Armillaria
spp. have been noted in CO and OR.
F UNGI
THE GREAT
DECOMPOSERS
Fungi recycle Fungi
recycle
nutrients by breaking down dead plant material. Fungi that live on dead plant material are called are called
saprophytes. M EET THE T ROPH FAMILY
 Autotrophs
 Biotrophs
 Necrotrophs
A UTO T ROPHS

SSynthesize their own nutritional needs th i th i
t iti
l
d
(photosynthesis)

Example: Green Plants
B IOTROPHS
Biotrophs are are
also called obligate parasites.

An organism that can only live and A
i th t
l li
d
reproduce on another living organism

Example: powdery mildews, downy mildews, rust fungi
N ECROTROPHS

Example: Sclerotium rolfsii causes
rolfsii, causes southern blight/southern stem rot. This stem rot. This
fungus survives by producing spherical p
resting structures called sclerotia.
A parasite that kills and obtains its A parasite that kills and obtains its
nutrition from dead host cells
E XAMPLES
F UNGAL
D ISEASES
OF

Mildews (Powdery and Downy)

Rusts and smuts

Vascular wilt diseases
Vascular wilt diseases

Root and stem rots

Leaf spots and blights
P OWDERY M ILDEWS
Powdery mildew y
can be managed with fungicides. Sprays can be initiated after initiated after
signs of disease are visible, but don’t wait too late.
Powdery mildew on English oak.

EEasily il
identified by white mycelium

Resistant species and cultivars are available for lilac, dogwood, crape myrtle, phlox
phlox, crabapple
D OWNY
Downy mildew of impatiens has damaged landscape plantings in the U.S. in 2011 and
U.S. in 2011 and 2012.
MILDEW ON
I MPATIENS
B OXWOOD B LIGHT OF
B OXWOOD
Defoliation of boxwood in one season due to b
boxwood blight d bli ht
(Cylindrocladium buxicola). Boxwood blight g
was first discovered in the U.S. in NC and CT in Oct 2011
in Oct 2011.
Photos courtesy of M. Inman, CT Ag Exp Station
R USTS
Cedar apple rust C
d
l
t
is a heteroecious
rust, requiring two unrelated hosts to complete its lifecycle. Autoecious rusts rusts
only require one host to complete their lifecycle.

Yellow leaf spots and rust colored pustules

Numerous hosts including conifers, broadleaf plants

May also cause galls, y
g ,
twig dieback
A PPLE S CAB

Found on apple and crabapple 
Causes premature leaf drop

Symptoms may be found on leaves and fruit

Also found on pyracantha
A NTHRACNOSE D ISEASES

Fungal leaf spot, twig blight and/or canker disease
k di

Favored by cool, wet weather

Hosts: ash, ,
dogwood, maple, oak, sycamore
F UNGAL C ANKER DISEASE
Localized infection, often causing b
branch dieback
h di b k
May follow drought stress
Prune out dead branches to stop spread
1
YEAR L ATER - C ANKER HAS
MOVED TO MAIN S TEM
To prevent: irrigate to minimize water i i i
t
stress
Prune out dead branches when they are th
observed or you could lose the
could lose the whole plant
R OOT ROT DISEASES

Affected plants may be stunted, wilted wilted

Discolored, decayed roots
decayed roots

Poor drainage, standing water
standing water, excessive irrigation, favor disease development
Ph t hth
Phytophthora
roott rot/juniper
t/j i
B LACK R OOT R OT – F OLIAR
S YMPTOMS
Black root rot is caused by the fungus Thielaviopsis. BRR causes a slow, progressive progressive
decline. Initial symptoms are yellow foliage; roots of infected plants are discolored and decayed.
R OOT
Dark, discolored roots on Japanese and blue holly, and bl h ll
d
inkberry are almost always a symptom of y p
black root rot. Herbaceous hosts include: pansy vinca
pansy, vinca, petunia
SYMPTOMS OF BLACK
ROOT ROT
B ACTERIA
 Single celled organisms much organisms
much
smaller than fungal spores
 Not visible to the naked eye
 Shaped like rods, spheres, helical
B ACTERIAL D ISEASES

Soft rots

Vascular wilts

Leaf and fruit spots
Leaf and fruit spots

Crown gall

Fire blight

Citrus canker Citrus Greening
Citrus canker, Citrus Greening
B ACTERIAL L EAF S POT
Xanthomonas
leaf spot on English ivy. English ivy
B ACTERIA
Bacteria streaming from a portion of a cabbage leaf bb
l f
infected with black rot. Photo courtesy P. y
Bachi, Univ of KY.
STREAMING FROM
PLANT TISSUE
C ROWN GALL
Crown gall on a wisteria a wisteria
stem

Tumors/galls on stems/roots

Soft, spongy to wooden to wooden
and corky with maturity

Bacteria enter through wounds
F IRE B LIGHT
A bacterial disease of apple, crabapple and
crabapple and pear. Symptoms at right include a classic symptom for fire blight, a “shepherd’s crook” and a crook
and a
stem canker.
B ACTERIAL LEAF SCORCH
Leaf hoppers are the insect vectors of bacterial leaf scorch The
scorch. The xylem inhabiting bacterium that is the causal agent plugs those vessels that transport water to leaves
to leaves resulting in leaf scorch.
Bacterial , vascular wilt disease of shade trees, especially pin oak