There are two main classifications for plant and tree disease: abiotic and biologic.  Abiotic disorders are caused by non-living factors that have an effect on the health of a plant, such as water, sunlight, and nutrient requirements.  Biological disorders are caused by parasitic organisms thriving inside of plants.  Plants growing in the wild maintain a healthy internal balance by living in a farily stable environment. Preventing "dis-orders" of landscape plants can be done with a fair amount of success by proactively maintaining their less-than-nautral environment.

The general health of a tree should be fairly obvious when all of its limbs are full of green leaves.  Various forms of disease can be properly identified by wilting or abnormal coloring of leaves, and sections of limbs beginnng to die.  Bark is the trees' first line of defense against disease...