CEDAR-APPLE RUST (Gymnosporangium juniperi-virginianae).
general on red-cedars and sometimes on other junipers and is very
common in home gardens where red-cedars and native flowering crab-
apples have been inter-planted. Galls on the cedars are enlarged needles,
varying from a fraction of an inch to 2 inches across. They are brown,
round, or slightly kidney-shaped, and covered with small circular depressions from which in wet spring weather orange gelatinous spore
horns are sent out (Figure 46). When covered with horns, the cedar gall
is a very gay affair and may reach the size of a small orange. Winter
spores embedded in the gelatin produce little sporidia which are carried
by wind to apples and crabapples.
By midsummer leaves of this host
have circular orange-red spots each with a circle of tiny black dots on
upper surface and there are wreaths or clusters of little brownish cups
on the undersurface. The same cup-shaped fruiting bodies appear at
the stem end of apples, sometimes on swollen crabapple twigs. The
wind carries these summer spores from the apple back to junipers, where
the galls take 18 months to mature and start a new cycle. The cedars
are not much harmed by the rust, but apples lose their leaves prematurely
and the fruit is dwarfed or deformed. All native crabapples are susceptible, with Bechtel's crab losing branches and sometimes dying. Oriental
varieties are mostly resistant.
Control. Planning to keep the two hosts separated is best. Red-cedars
are forbidden by law in some apple-growing sections. In home gardens
cut galls off cedars in winter and early spring before they put out spore
horns. Spraying apples regularly with Fermate and sulfur through spring
and summer and spraying junipers with wettable sulfur in early spring
and late summer control the disease but this is a more ambitious program
than most home owners care to undertake.
HAWTHORN RUST (Gymnosporangium globosum).
This is another cedar-
apple rust, but the galls on the juniper host are a little smaller,
seldom over 1/2 inch, and mahogany brown in color. Besides hawthorn,
summer hosts include apple, crabapple, pear, and mountain-ash.
HOLLYHOCK RUST (Puccinia malvacearum).
There is no alternate host
for a rusr that is coexistent with hollyhocks. Reddish to orange
powdery spore pustules are formed on the underside of leaves and in
elongated lesions on the stems. The upper side of the leaf is usually yellow
in the areas over pustules, which sometimes turn grayish with production
of sporidia Heavily infected leaves may wither. The fungus winters
in old leaves and stems.