Gall Rusts of Pine
Gall Rusts of Pine
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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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