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Picture of the Week for
24 April 2000

Western Pine Gall Rust

Karen Rane, Disease Diagnostician

These galls are typical symptoms of one of the gall rust diseases, most likely western pine gall rust. This rust disease does not have an alternate host, so the spores that are produced in the galls are able to infect pine shoots resulting in numerous galls of various ages in a single tree. Spores are released from the galls in spring (late April to June) when the fungus breaks through the bark of the gall forming cream-colored blisters that turn orange with mature spores. The spores infect current-year shoots of pines, and small galls appear a few months after infection. Galls are usually 1-2 years old before sporulation occurs. The galls are perennial - that is, spores are produced each growing season for several years.

Western gall rust is the disease commonly found in Indiana, but the galls are indistinguishable from those caused by the eastern gall rust fungus (which has oak species as the alternate host).

Sanitation is key to managing gall rust diseases. Inspect all nursery stock prior to planting for any evidence of swellings or galls, and avoid planting any symptomatic seedling. Prune out and destroy galled branches in established trees to reduce the amount of spores available to cause infection. In nurseries and Christmas tree plantations, it may be most efficient to remove entire trees if there are numerous galls on branches. Due to the length of time needed before the galls are easily noticed, it will take a few years of close inspection to detect all infected trees in a plantation. Dithane M-45 is labelled for pine rusts, and should be applied when spores are being released and shoots are elongating. The fungicide is a protectant, and will not cure trees with galls. If you have additional questions concerning management of this disease, please contact Dr. Paul Pecknold, extension pathologist for ornamental crops, at 765-494-4628.

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Last updated: 1 May 2000/tlm.