PINE-PINE GALL RUST ( Endocronartium harknessii )
Pine-pine gall rust is caused by a fungus, and is a common disease of Scots pine. Jack pine, native to northeastern New York, is also highly susceptible. Many native western pines and introduced species, such as Austrian and mugo pine, are also reported to be hosts. Pine-pine gall rust causes the formation of spherical woody galls on branches and stems of pine.
Galls may get to be as large as softballs, but most are about the size of a golf ball. They form in response to the presence of the fungus in the vascular cambium. Galls may grow for 2-4 years after the initial infection before they develop the fruiting bodies (aecia) that produce spores to cause new infection.
Fig. 1. Sporulating galls on a branch of Scots pine
On Scots pine in New York State, the fungus begins to produce spores beneath the bark on the galls in mid-late May, at which time the bark begins to crack open, exposing a mass of brilliant yellow-orange spores. The spores are wind disseminated, and when they land on tender elongating shoots new gall formation may begin. Spores are usually produced for at least 3 weeks every spring.
The fungus needs living tissue to survive and will quickly die when the tissue it is growing on is cut. When galls are discovered on a particular tree, simply cut off the diseased branches. Rogue heavily infected trees or small trees with a gall on the main stem. Where a large percentage of trees (more than 5%) in a given plantation are found to be susceptible, a fungicide may be used to try to prevent new infections from getting started.
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