Biology Reference
In-Depth Information
Gymnosporangium exiguum III on leaves of
alligator and Mexican junipers, eastern red-
cedar; 0, I on leaves, fruits of hawthorn.
Gymnosporangium exterum III on stems of
eastern red-cedar; 0, I on gillenia. Flattened telia
anastomose over short fusiform swellings with
roughened bark on cedars. Also galls on stems
of juniper.
Gymnosporangium floriforme III on red-
cedar; 0, I on leaves of hawthorn. Cedar galls
are small.
Gymnosporangium fraternum (
G.
transformans
). III gall on
Chamaecyparis
thyoides
; 0, I on chokeberry.
Gymnosporangium globosum
Hawthorn Rust
,
III general on eastern red-cedar, also on dwarf,
prostrate, and Rocky Mountain junipers; 0,
I mostly on hawthorn, also on apple, crabapple,
pear and mountain-ash. Leaf galls on cedar are
very similar to those of common cedar-apple rust,
but are smaller, seldom over 1/2 inch, nearer
mahogany red in color, and not perennial, pro-
ducing telial horns one season only. Apple and
pear foliage may be slightly affected but not the
fruit; aecia are common on hawthorn pips.
Gymnosporangium gracile III
Witches'
Broom
on juniper; 0, I on hawthorn, quince, and
shadbush.
Gymnosporangium asiaticum III on leaves of
Chinese juniper; 0, I on Chinese flowering quince
and pear.
Gymnosporangium harknessianum III on
western juniper; 0, I on amelanchier, chiefly on
fruits, sometimes stems. Papery margins of aecia
are usually long.
Gymnosporangium hyalinum III on southern
white-cedar; 0, I on hawthorn and pear leaves.
Slight swellings are formed on small twigs and
branches of white-cedar.
Gymnosporangium inconspicuum III on Utah
juniper; 0, I on fruits, mostly of amelanchier and
squaw-apple. Juniper leaves turn yellow; rarely
telia appear on branches.
Gymnosporangium japonicum (
G. photiniae
).
III gall on stems of Chinese juniper; 0, I on
photinia.
Gymnosporangium
cedar, eastern and southern, on prostrate and
Rocky Mountain junipers; 0, I general on apple
and crabapple east of Great Plains. The fungus is
a native of North America and does not occur
elsewhere. It is more important commercially in
the apple-growing regions of the Virginias and
Carolinas and certain states in the Mississippi
Valley. It is important in many areas on ornamen-
tal crabapples in home plantings.
The cedar “apples” or galls vary from 1/16
inch to over 2 inches across. Leaves are infected
during the summer, and by the next June a small,
greenish brown swelling appears on upper or
inner leaf surface. This enlarges until by autumn
the leaf has turned into a chocolate brown, some-
what kidney-shaped gall covered with small cir-
cular depressions. The next spring in moist
weather orange telial horns are put forth from
the pocketlike depressions. The teliospores are
enveloped in a gelatinous material that swells
vastly, a gall covered with horns sometimes
reaching the size of a small orange. They germi-
nate in place to produce the basidiospores, which
are carried by wind to infect apple or other decid-
uous host.
By midsummer, apple leaves show yellow
areas with amber pustules on upper surface; but
after pycnia have exuded drops of sticky liquid,
they appear as black dots in a rather reddish
circle. On the undersurface of these spots small
cups are formed, with recurved fimbriate mar-
gins. These aecia may also appear near stem end
of apples and are common on swollen twigs of
crabapple. Spores from these cups are blown
back to the cedar in late summer, the entire
cycle thus taking 2 years, 18 to 20 months on
the cedar, 4 to 6 on the apple host.
Chief injury is to the apple host, the rust caus-
ing premature defoliation, dwarfing and poor-
quality fruit. On very susceptible crabapples,
such as Bechtel's crab, repeated infection may
cause death of the branches or of the entire tree.
All our native crabapples are susceptible; most
Asiatic varieties are resistant.
Control
Care in planning is most important.
Don't let your landscape architect or gardener
put cedars and native crabapples or hawthorns
close together. Keep them separated as far as
juniperi-virginia-
nae
Cedar-Apple Rust
.
III general on red
