Michigan State University Extension
Ornamental Plants plus Version 3.0 - 00001698
11/12/99
Gall Rusts of Pine
Two gall rusts of pine occur in the north central states:
the western gall rust, caused by Endocronartium harknessii
(Cronartium coleosporioides); and the eastern gall rust,
caused by Cronartium quercuum. If the rust is on Scotch
pine, it is invariably the western gall rust; if the rust
is on jack pine, it is usually the eastern gall rust. The
western gall rust may move from Scotch to jack pine but
seldom from jack pine to Scotch pine.
The symptoms of the two gall rusts on pines are identical.
Spores germinate and invade the pine needles when a water
film is present on the needle surface for at least 18
hours. The fungus moves into the wood and causes
excessive growth of the plant's cells. Therefore, the
galls consist mostly of woody tissue. The gall disrupts
the sap flow, often girdling and killing the part of the
tree above it. The galls are usually spherical but
sometimes are apparent only as a flat or distorted area on
the stem.
Galls on the main stems will kill trees, and multiple
galls on branches can decrease the value of Christmas
trees. Other fungi, such as the blue stain fungi,
frequently enter the pine through the galls and cause
other problems.
Galls are formed at the end of the first or second growing
season following infection. During May and June, light
orange masses of spores occur on the galls. In eastern
gall rust, these spores cause infections on red and black
oaks. A different spore type then forms on oak leaves in
summer and returns on wind currents to infect new pines.
Problems in the landscape caused by the eastern rust are
due primarily to the close proximity of heavily infected
oaks. The youngest leaves on the oak, particularly those
on sprouts, are usually infected. In western gall rust,
the masses of spores in the gall reinfect other pines
rather than oak. Severely infected trees will become
stunted and yellow and form "witches'-brooms."
Either gall rust infects pines only through the current
year's needles when needles begin to break through the
fascicle sheaths on elongating shoots. This occurs in
late spring when candles are 50 percent of their maximum
length. The fungus in the galls pushes through to the
outer surface of the gall and releases the air-borne
spores from approximately spring to early summer.
Control: Prune out galls.
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This file was generated from data base ZZ on 01/19/00.
Data base ZZ was last revised on 11/12/99.
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