The dieback of Monterey Pines is caused by the disease Pitch Canker (fungus Fusarium circinatum). Insects (beetles) carry and transmit the disease from one tree to another. The fungus causes infections which obstruct the flow of water and eventually the needles/branches die off.
The disease was first noticed in Santa Cruz back in 1986 and now has numerous occurrences along the entire California coast line. The fog that we get here in the Bay Area creates the needed extra moisture for the fungus to grow. In the inland areas the fungus doesn’t take as strong of foothold. Records are showing that urban environments containing landscaped areas show a higher incidence than the less disturbed forests.
Not all diseased Monterey Pines will completely die off when infected. Some may recover over time and some will become resistant to the disease. Homeowners and land managers can take a conservative approach to removal of infected pines due to the possibility the tree may recover. However, once the entire tree turns brown, showing no green, then removal is necessary. Complete removal of all branches and wood from the property is recommended. California State Board of Forestry has designated a zone of infestation that includes most of coastal California and has set forth Guidelines for Handling Woody Material Infested with the Pitch Canker Fungus. The pathogen can survive in the firewood, seeds and soil.
Infected branches can be pruned out eliminating the disease but new infestations can reoccur. The pruning can be used to enhance the aesthetic quality of the tree and delay the removal from the environment.