Bark Beetles

What Landowners Need To Know About Identifying, Removing, and Preventing Pine Bark Beetles

Beetles are devastating the forests in North America. Specifically, the bark beetles have reached the Ponderosa Pine trees in the Saltese area and have begun to destroy the local habitat. I am very concerned that left unchecked, the bark beetle will destroy the mature Ponderosa trees in this area.

Can Bark Beetles Be Stopped?

Since the first year bark beetles attacked the Ponderosa Pine trees on my property in 2019, the number of affected trees increased each year, until I managed to find a treatment that completely stopped the attacks. In 2022 and 2023, I did not lose any trees to the bark beetles, nor did my neighbor who allowed me to test the treatment on his trees as well. During the same period, adjacent property owners who didn’t use the same treatment lost many trees on their property to the Bark Beetles.

How did I stop the bark beetle attacks? By following these three steps:

  • Step 1: Identify the trees that have bark beetles in them.
  • Step 2: Remove the trees with bark beetles.
  • Step 3: Spray all healthy trees with an insecticide in May.

A more detailed explanation of my treatment follows.

Bark Beetle Life Cycle

Understanding the beetle’s life cycle is important in stopping it, because the treatment depends on timing the cycle correctly. The image below shows the life cycle of the Mountain Pine Beetle, one of the four types of beetles infesting the trees in the Saltese area (which all have similar life cycles). There is additional information about all the different types of beetles at the bottom of this page.

As you can see from the image, the time to treat is in the winter when the beetle is in the larva stage. It is almost too late to treat once the beetle is an adult in the summer and infecting more trees.

How to Get Rid of Bark Beetles

Step 1. Identification: Signs of Bark Beetle Infestation and Damage

The first step is to learn how to identify a tree that has been infested with beetles. Here are the methods I have found useful when determining if suspected damage is from bark beetles. Most of the attacks I have witnessed are on Ponderosa Pine trees, so this information is specific to Ponderosa Pines, but I believe it is relevant to all trees that can be attacked by the beetles.

Tree Needles Turning Brown

The first indication of bark beetle infestation you will notice is the needles on an entire branch of a tree turning brown. Generally, the whole tree does not turn brown at once, but it starts in the middle or top and begins to spread (see the picture below as an example). Some Ponderosa needles regularly turn brown each year and fall off, so don’t be alarmed if your trees have a few brown needles. You should continue your investigation if you are unsure before making a final decision. Once you become more familiar with the issue, you will easily be able to identify whether the tree is being attacked.

Initial bark beetle attack on Ponderosa Pine

Green Needles: Straight and Green or Drooped and Yellowing?

The next step in your investigation is to look at the green needles on the rest of the tree. Do those needles look green and straight or are they beginning to droop and look yellowish? Look at adjacent trees, are their needles all straight and green or are some of those trees looking yellowish and drooping? If there are a lot of green needles drooping, that is my key indicator that the tree has beetles.

Brown and green needles drooping which indicates the beetles will likely kill this tree.

Pitch Tubes in Bark: White or Reddish-Brown?

If you suspect the beetle is in the tree, look at the tree’s bark. Trees react to bark beetle attacks by releasing pitch as their natural defense. This response from the tree will leave small white or reddish-brown pitch tubes on the outside of the bark. A white pitch tube means the beetle was successfully repelled by the tree.

White pitch tube with beetle expelled.

If the pitch tube is reddish brown, most likely the beetle was successful in attacking the tree. The pitch from a successful attack with likely be accompanied by a sawdust-like substance, called frass, created by bark beetles and their larvae as they bore through the bark. I haven’t seen the pitch tubes as much as the other indications of a beetle attack.

Red pitch tube with saw dust suggests a likely successful attack.

Holes in the Bark: Two Types

If you see tiny round holes in the bark as shown in the picture below, these are likely exit holes from beetles that have hatched in the tree and exited the tree.

Beetle exit holes in Ponderosa Pine

You may also see evidence of larger irregular shaped holes created as birds peck at the tree to eat the beetle larvae, as seen in the picture below. .

Bird peck holes where the birds are eating the larvae in the tree.

Larvae and Channels Inside Bark

If you have all these signs, unfortunately, it’s not looking good. Finally, peel off a small section of the bark around the holes. It will probably come off easily if there are beetles or larvae behind it. If there was a beetle attack, you will see larvae and the channels where the larvae are feeding on the tree. (See picture below).

Beetle larvae and feeding channels under the bark of a Ponderosa Pine. Note the large and tiny larvae. There are also some wood chips in the picture so not everything that is white is a larva, but there are a lot of small larvae in the picture.

Now, you can scream!

You need to remove the infected trees.

Step 2: Removal of Beetle-Infested Trees

Timing is crucial for both removing and spraying

  • If you discover bark beetles during May-October, DO NOT REMOVE THE TREES YET. The beetles are active, and it will just spread the beetle when you drop the tree and they look for a new food source in unprotected bark. Wait until winter when it is colder, because the beetles will be dead and only the larvae remain. Instead, during these warmer months it is important to spray the tree and all adjacent trees with an insecticide. It will not kill the beetle in the tree, but will kill the beetle when it leaves the tree, and will also kill any beetle trying to enter adjacent sprayed trees.
  • Remove infected trees in the winter. You do not need to spray the infected trees in the winter.

What to do with cut wood infected with bark beetle

Once you have cut down the tree in winter, you’ll need to deal with the wood effectively to avoid further infestation.

What wood is infected?

  • Signs of infected wood:
    • If there are still some green needles on the tree, it is likely the larvae are still in the tree.
    • If all the needles are brown and the bark on the tree is heavily pecked by birds, it is likely the larvae is gone.
    • After you cut the tree down, look for the blue stain on the wood as you cut it into sections. The beetles carry a fungus which dyes the wood blue in color. This is an indicator of where the beetle has attacked, or larvae is living in the tree. I cut 10 feet further than the stained area each way. I consider all of that wood as infected. I also look for signs of the beetle in portions of the tree that don’t have the stain, to ensure complete eradication. However, to be safe, you can consider all the wood in the tree as infected.
Blue-stained wood from beetle fungus

What to do if the wood is infected:

  • Don’t give the wood away. This only spreads the problem to others.
  • Don’t pile the wood and leave it. This just attracts more beetles.
  • Wait until winter and chip the branches. Spread the chips so any remaining larvae will die in the cold.

Note: If using a commercial tree removal company, make sure they have a plan to not spread the beetles. Hopefully, they have a chipper large enough to chip the branches and the trunk.

How to kill bark beetles and larvae on cut wood you are unable to chip:

  • Debark and destroy: Bark beetles feed on inner bark, so debarking logs will eliminate their food source. Destroy the infested bark by burning, landfilling, or chipping. This is the method I use on wood that is too large to chip.

OR

  • Burn: Get a burn permit and burn the wood. You can get a permit from the Department of Natural Resources (DNR) to burn wood for this purpose

OR

  • Solarization Method: Cover the wood with a double layer of loosely-wrapped clear plastic. Soak the logs with water prior to covering with plastic, to promote mold growth and further deter beetle development. Stack wood two logs high, and place it in a location where it will get full sun. Seal the edges of the plastic in trenches covered with soil. The beetles cannot survive the heat under the plastic. You will need to keep the wood covered through the summer for the temperature to get high enough. See picture below.
Beetle-killed wood being treated using the solarization method. Tom DeGomez, University of Arizona

Step 3: Preventing Bark Beetle Infestation and Spread

Keep your forest healthy

A healthy forest is the best prevention for pine bark beetles. Trees need water and sunlight to survive. Thin trees so they get sun and do not have to compete with other trees for water during the dry summer months. My rule of thumb for thinning is space trees so that they are greater than 16 feet apart for small- to medium-sized trees. For trees greater than 50 feet tall, use 24-feet spacing. Another rule of thumb is to remove trees once the branches start touching the branches of other trees. The picture below shows an unhealthy forest where the trees are too close together.

Trees too close for a healthy forest

Apply an insecticide in the spring

I use an insecticide called MAXXTHOR EC. You can find this insecticide at Bugspray.com. MAXXTHOR is highly repellent to the beetles and when applied to the bark of the tree will keep the beetles away for months. Even trace amounts will cause them to forage elsewhere. An added benefit is that helps control the mosquitoes and ticks. The active ingredient is Bifenthrin which is highly effective at killing insects, has low toxicity to mammals, and has good biodegradability. I spray once a year in May. Below is a list of the steps I use for spraying.

  • Use a pump sprayer, hose sprayer, or motor-driven sprayer.
  • Fill the sprayer with a mix of 1 oz insecticide per 10 gallons of water. Always read the directions for mixing and applying the spray. My mix rate may vary from the rate you decide is best for your application.
  • Add a wetting agent (surfactant) to the spray mix to help it stick to the tree. A basic wetting agent is dish soap, or you can purchase surfactants at your gardening store.
  • Spray the tree until it is dripping.
  • Spray all sides of the tree.
  • Spray to the top of the tree if you can reach it. If you can’t reach the top, spray as high as you can. In my opinion some spraying is better than no spraying. I have a commercial sprayer that will reach 60 feet so I can get to the top of most trees. Early experiments with a sprayer that only reached 30 feet proved effective.

Use pheromones to repel beetles

To prevent overcrowding of a tree, mountain pine beetles naturally release anti-aggregation pheromones to repel additional attacks from other beetles. The pheromone signals to other beetles that this tree is fully occupied, and to go find an unoccupied tree. These pheromones have been packaged and can be purchased as a repellent. The efficacy of pheromones is reduced when mountain pine beetle population densities are already high. I have not found pheromone treatments to be effective, but other neighbors have had success when Verbenone SPLAT Verb Paste is applied to every tree in the spring.

Can a Tree With Bark Beetles Be Saved?

  • Once the beetle has attacked a tree, it is very unlikely you can save the tree. The beetle eats its way around the inner bark of the tree destroying the tissue where the pitch and water flow to the crown. Also, the beetles carry with them the spores of blue-staining fungi. The fungi are introduced into the sapwood as the beetles excavate egg galleries under the bark. The fungi further aid the beetles by interrupting the nutrients from getting to the tree.
  • If the attack is in the middle to the lower portion of the tree, the tree is likely gone and will need to be removed.
  • If the attack is at the very top of the tree, you may have a chance. However, you will need to use a different treatment method and it’s important to note that it has worked on only trees where I have top-kill. Here is a link to a video https://youtu.be/OsbI8DT9lC0 that explains a root treatment to attack the beetles from within the tree. The root treatment is about 9:40 minutes into the video.

Below are links to useful information I have found to help manage the Bark Beetles.

See the post They’re coming for our trees