Disorders affecting the health of a tree can be difficult to diagnose. Diagnosis requires a combination of experience, knowledge and keen observation. Infestations and diseases are usually a secondary factor and arise because a tree is already suffering from a combination of stress factors including mechanical injury, temperature extremes, chemical injury, grade changes, nutrient deficiencies and construction damage.
Part of dealing with disease or insect infestations is correct identification by recognizing symptoms and causes.
Follow this link if you wish to do your own investigating into possible infestations and diseases.