General Info

What is a pathogen?

A pathogen is an organism that causes illness or disease in another living organism. The organism the pathogen is feeding off of, known as the host, can be pretty much any living creature.

The host range is which species the pathogen is able to grow on. For example, Swiss Needle Cast’s host range is mainly Douglas-fir. The pathogens that infect trees are usually fungi. Mushrooms are the most recognizable form of fungi, but there are many other types that do not form mushrooms. Mushrooms are the fruiting bodies of a fungus, like what an apple is to an apple tree. If you see the a fruiting body, that is known as a sign.  The main fungal organism, made of a filamentous growth form called mycelium, grows underground. For this reason, you might only be able to see the external symptoms of a pathogenic fungus, such as the browning decay of leaves on a tree or the unhealthy yellowing of conifer needles.

Browse our pathogen species list to learn about the common fungal pathogens of western Washington!