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Alaska AK Tree Services
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Western Gall Rust

Knobby growths, technically referred to as galls, on the branches of pine trees are often caused by a tree disease called Western Gall Rust. Like most other tree diseases, Western Gall Rust is spread from tree to tree by spores. These spores germinate on pine needles and eventually infect the twig or trunk of the tree.

Western Gall Rust derives it nutrients from the vascular system of the host tree, but rarely kills the branches it lives on. By altering the growth hormones in the tree galls of varying sizes are formed near the site of the infection. While most galls are formed on tree branches occasional galls will develop on the trunk of the tree.

When dead pine branches are seen on infected trees it is usually due to a secondary organism. Nectria canker - another type of tree disease, or borer insects are common causes of branch death of trees infected with Western Gall Rust.

Western Hemlock Dwarf Mistletoe

Western Hemlock Dwarf Mistletoe is most commonly found in southeast Alaska. Mistletoe is a parasitic plant that, although it can photosynthesize sunlight, derives most of its nutrients from its host plant.

Like Western Gall Rust, Western Hemlock Dwarf Mistletoe affects the growth hormones in the host plant. Dense-clustered branch distortions, called witches' brooms, are formed when a tree is infected with mistletoe. When the main trunk of a tree is infected with mistletoe it may form a large swelling called a burl.

An interesting aspect of Western Hemlock Dwarf Mistletoe is the manner in which its seeds are developed and dispersed. After a mistletoe plant is pollinated it takes more than a year for the seeds to develop. When mistletoe seeds are mature they erupt from their seed pods and are covered with a sticky coating. The mistletoe seeds can infect the same tree in a different area or be picked up and carried to a new host tree by birds, squirrels, or other animals.

Although it is a unique disorder of trees it should be noted that severe infections of Western Hemlock Dwarf Mistletoe can kill a tree.

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