Threats to the campus forest
The Monterey Pine tree (Pinus radiata) is one of the most represented tree species on campus. Many of these trees were planted when the campus was founded. They are native to northern California, fast growing and provide a distinctive look to the campus forest and grounds. 40 % of the interior campus forest is made up of Monterey Pines.
These beautiful trees are susceptible to two main natural threats the Red Turpentine Beetle and Pine Pitch Canker.
Red Turpentine Beetle
The red turpentine beetle is a beetle that boars into the bark of trees where they mate and lay eggs. The larvae feed, pupate, and winter under the bark. They emerge in the spring as adults and seek new trees to infest. On the SFSU campus there are two flights of beetles annually one in the spring and one in the summer.
Trees most likely to be attacked
Trees are attacked by the red turpentine beetle when they are weakened or stressed. Trees become stressed or weak due to:
- - Drought - Lack of rain or lack of irrigation
- - Poor Nutrients - Lack of fertile soil or lack of fertilizer
- - Damage to roots - Cuts from construction, mechanical equipment, compacted soil
- - Damage to branches - Pruning, Breaking, Storm/wind damage, infestation
- - Damage to trunk
- - Infestation of pests - Insects, fungi
- - Disease
Number of Bark Beetle Attacks on the SF State campus
- - Total new attacks: 12
- - New attacks on trees with previous attacks: 10
- - New attacks on trees without previous attacks: 2
What we are doing about it
There are a variety of strategies for deal with red turpentine beetle infestations. Through integrated pest management (IPM) the campus is taking the following measures:
- Twice a year in the fall and spring to take advantage of the rainy season the trees are fertilized. This increases tree vigor allowing the tree to repel beetle attacks.
- Deep watering
- The shallow watering that is used for lawns does not reach the root system of trees and encourages shallow unstable roots. In times of drought periodic deep watering will allow trees to get the moisture they need for resin production. The best defense trees have for fending off the beetles is the production of sap that the tree uses to push the beetles out of the holes they are attempting to bore.
- Pruning schedule
- Tree pruning is essential to the health of the tree and the safety of the campus community. Dead, dangerous, broken are removed from trees by the grounds department. The removal of limbs causes the tree to release a chemical that attracts the beetles. By pruning out of the beetle season the grounds department ensure the health of the tree and the campus. Trees are not pruned between February and November when beetles can be active.
- Trees are regularly inspected for evidence of red turpentine beetle attack. When the beetles begin to boar into the tree the tree responds by t\releasing resin. This resin forms a pitch tube. As the tube ages it turns from bright ref\d to pink to yellow to white. The age of a pitch tube can be determined by the color of the tube. The presence of a tube should not be seen as evidence of a successful attack, only an attempted attack. Boring dust and Frass are indicators of more serious problems and require closer monitoring.
- Insecticide spraying
- Trees that have low levels of attacks, have been recently pruned, are otherwise stressed or near trees that have high levels of attacks are spayed with an insecticide before the first beetle flight in February. A second spaying may take place in summer before the second flight. Spaying is only effective before the beetles infest a tree. Once the beetles are below the bark they are not affected by the spray.
- Trees that are dead or dying are removed by the campus. Trees are removed when the pose a significant risk to the campus community and/or other trees.
Pine Pitch Canker (PPC)
Pine Pitch Canker is a disease of pine trees caused by a fungus. The Monterey Pine tree is particularly susceptible to the infection.
- Evidence of Pine Pitch Canker
- Resin oozing down the trunk of the tree without apparent wound to the trunk
- Cankers that ooze pitch on the branches or trunk of a tree
- Dead needles at the tips of branches
- Ugly but living
PPC is unsightly and the oozing sap can cause concern. However many trees are resistant to infection or develop resistance over time. Trees that have been severely infected will often heal themselves. This is not a guarantee but the best practice is to monitor the tree and only prune branches or remove if the tree is dying.
The rate of pine pitch canker infection on the SFSU campus is slow. About every two years 2% more trees are infected. The infection severity within an individual tree changes over the course of the years. New infections and the progress of old infections are monitored by grounds staff through frequent inspections.