Stressed Torrey pine trees falling victim to insect attacks

Torrey Pines Golf Course is nationally recognized as one of the premier golf venues on the West Coast. From hosting its annual Farmers Insurance Open tournament to being a hot spot for tourists to San Diego, the 36-hole course has become historic in the golf world.

Over the past five years, however, the California drought has jeopardized the course’s iconic Torrey pine trees. With higher temperatures and less rain, bark beetles have continuously attacked the trees, and they are dying as a result.

Bark on the Torrey Pine tree is falling off due to beetle attacks. (Photo by Jacob Sandoval)

“The higher temperatures are, the more stress the pines are under,” said Edward Drobnicki, horticulturist at Torrey Pines Golf Course. “And when the trees are under high stress, these bark beetles attack them with no mercy.”

According to Drobnicki, the north and south sections of the Torrey Pines Golf Course lost roughly 20 percent of their pines in the past year as a result of bark beetle attacks.

As the pines grow more stressed, they release a pheromone that attracts more beetles toward the already dying trees.

“Bark beetles build up large populations in areas that have undergone severe drought stress,” said Bobbie Orr, board certified entomologist for Rentokil Steritech North America. “And beetles can produce three generations within a year under these climate conditions.”

Recognizing that the Torrey pine is the rarest native pine in the U.S., the course has taken immediate action in hopes of preserving the trees. The first action included setting up six pheromone traps across the course.

Pheromone traps are located across the North and South courses at Torrey Pines. (Photo by Jacob Sandoval)

“We spread these traps across both the north and south course with the hope of the beetles being attracted away from the pines,” Drobnicki said. “Once the beetles are stuck in these traps, they can’t get out and their population within the pines decreases.”

Although the traps are effective, they only catch a small percentage of the overall beetle population. As a result, the traps are mostly used to monitor the beetles, Drobnicki said.

The traps capture the pine-killing beetles and prevent them from escaping. (Photo by Jacob Sandoval)

Therefore, in addition to placing the pheromone traps across the course, Torrey Pines injected 227 trees with a systemic insecticide. The system of injections the course uses is called Arborjet.

“The process of the injections is a simple drill-plug-inject method,” Drobnicki said. “Holes are drilled at the base of trees and filled with a systemic insecticide that’s used to fight off the beetles and keep the pines healthy.”

Holes are drilled into the trunks of the Torrey pine trees to begin systemic injections. (Photo by Jacob Sandoval)

Furthermore, the most natural tool the course uses as a means of fighting off the beetles is rainfall.

“Water is great for the trees because water can sap out the beetles,” Orr said. “Therefore the more rain, the better.”

According to Drobnicki, the recent downpour that San Diego County experienced this past winter was great for the pines.

“While the rain was little too late for some of our trees, it was great for the ones that were fairly healthy and just beginning to experience attacks,” Drobnicki said.

Although Torrey Pines Golf Course has been proactive in its efforts to fight off the pine-killing beetles, an additional challenge it faces is tracking the level of damage the pines are currently experiencing.

“It takes months before the trees start showing symptoms of being attacked by bark beetles,” Drobnicki said. “A tree can seem perfectly healthy, when in reality, beetles have already started attacking it.”

According to Drobnicki, such symptoms include:

  • Lack of vigor
  • Dieback at the tips
  • No new needles
  • Fading in color of the needles
  • Lack of pointiness in the needles
  • Frass on the base of the tree

As a way of tracking which trees are healthy and which are dying, the course has placed number tags on the pines.

Bark beetles leave entry/exit holes during their attacks. (Photo by Jacob Sandoval)

Along with this method of monitoring the pines’ health, the golf course is currently in contact with researchers from North Dakota State University, who are working to develop more genetically diverse Torrey Pines that could potentially be more resistant to bark beetle attacks.

“The basis of our experiments is observing and monitoring pure island, mainland and F1 hybrid individual trees under varying climate conditions,” said Jill Hamilton, assistant professor of biological sciences at North Dakota State University.

According to Hamilton, they have been measuring these trees for the past 10 years. Some of their measurements include:

  • Tree height
  • Number of cones produced
  • Number of conelets produced
  • Reproduction within the garden

Although recent findings thus far show that F1 hybrids tend to grow substantially taller, produce more cones, are bigger and display a generational fitness advantage, continual monitoring is required to determine how the F1 will react under varying climate conditions, Hamilton said.

In addition to collaborating with Hamilton, Torrey Pines has planted more than 100 new pines throughout the north and south course.

“We’re planting more new trees than trees lost,” Drobnicki said.

While the growth of these new trees is going to take time, the beetles will remain present on the course, according to Orr.

“Tracking the attacking pattern of these beetles is already a difficult task,” Orr said, “and with so many already spread throughout the pines across the course, they’ll move to the newly planted trees and attack them.”

While the course is putting full effort into saving its pines, some golfers have come to notice dying trees across the course.

“On the north course especially, you can ride your cart around and spot dozens of trees that have nothing on their branches,” said Parker Doliber, a frequent golfer at Torrey Pines. “These trees look like they weren’t properly maintained and had the life sucked out of them because of warm weather.”

Little do frequent golfers, such as Doliber, know that the pines are a direct victim of the bark beetle attacks.

The build up of the California drought over the past several years has had a lasting effect on the pines at the golf course, and only time will tell how they respond, Drobnicki said.

“It’s challenging to predict weather,” Drobnicki said, “so at this point it’s a waiting game and the recommendation is to treat the pines again next spring.”

In the meantime, now that weather conditions are dry enough to get the proper equipment on to the course, Torrey Pines will begin removing trees that have already died.

In terms of the future, increased monitoring is essential for the trees to receive the proper treatment to fight off the beetles, Hamilton said.

“The beetles can never be defeated completely,” Orr said, “but if Torrey Pines can determine what trees are healthy now and treat them immediately, the pines will be able to fight the beetles off and the problem will decrease.”

For more information on how bark beetles are attacking pines all across the state of California, visit:

http://www.readyforwildfire.org/Bark-Beetles-Dead-Trees/