See:
Pine (Pinus spp.) - Cyclaneusma Needle Cast
Pine (Pinus spp.) - Dothistroma Needle Blight (Red Band)
Pine (Pinus spp.) - Elytroderma Needle Cast
Pine (Pinus spp.) - Lophodermella Needle Cast
Pine (Pinus spp.) - Lophodermium Needle Cast
Pine (Pinus spp.) - Medusa Needle Blight
Pine (Pinus spp.) - Salt Damage
Pine (Pinus spp.) - Sirococcus Shoot Blight
Pine (Pinus spp.) - Twig Blight
Cause Many different fungi and abiotic problems can redden, blight and/or kill needles on pines causing them to drop off the tree. The most common diseases identified by the OSU Plant Clinic include Dothistroma Needle Blight (Red Band) and Lophodermium Needle Cast. But needle cast diseases can easily be confused with one another. Over a dozen different fungi have been associate with needle problems by the OSU Plant Clinic. They are identified by microscopically examining fruiting bodies and spores. These fungi may infect only a few or have many Pinus species. These diseases are generally favored by wet weather and/or overcrowding that keeps needles wet for extended periods of time. Airborne or water-splashed spores infect young needles during wet weather, often during early spring growth. They generally survive unfavorable conditions in plant debris that may fall to the ground or be caught up in the tree.
Needle casts can also be confused with annual (normal) fall needle drop. Most conifers shed some of their oldest needles in the fall. These old needles often turn yellow or brown before falling off.
In most cases control tactics will be similar between the various needle cast diseases with a combination of cultural practices and possible use of chemicals depending on the growing site.