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Pine-Specific Pest Control

Most of us have heard about fungus attacking pine trees – both bonsai and trees growing in our gardens. I’ve done some internet research to learn more and wanted to share what I’ve learned. 

How Do You Know Your Tree is Affected?

If you see any of these then your tree is probably affected.

  • Are the needles yellow instead of the bright green that they should be at this time of year?
  • Do you see holes bored into your tree, with sap on the bark?
  • When you break a candle or branch is it dry? No sap?
Yellowed Needles on Black Pine
Yellowed Needles on Black Pine
Pitch Tubes from boring by adult bark beetles
Boring by adult bark beetles often results in pitch tubes; this one was caused by red turpentine beetle attacking Monterey pine. (Photo:Jack Kelly Clark)

What’s Going On?

We’ve had several years of drought here in California, with the result that in January 2015 it was estimated that 22 million trees were dead then and tens of millions were likely to die by end of 2015. Another estimate listed 20 percent of California’s forests, up to 120 million trees were doomed.

A side effect of this has been an explosion of bark beetles and other insects that feed on stressed trees. 

A Bark beetle is described as “… not much larger than a piece of cooked rice. Not only are they small and difficult to see, their activity is often scattered and hardly noticeable. They survive in trees that are stressed, diseased, or injured; either by human activity or during storms or wildfires. Occasionally, small groups of standing trees may be killed but over the landscape they are often unnoticed. Bark beetles can increase dramatically when sufficient food is available. Typically this is in the form of drought-stressed trees. High numbers of these small beetles (outbreak populations) attack trees en mass. Often many trees are killed over the landscape; likened to that of wildfire. In many years, more trees are killed by bark beetles than by fire!”

Interestingly once a beetle finds a target tree it exudes a pheromone that attracts other beetles to the same tree for a mass attack. The beetles carry a fungus into the tree that also attacks the tree. The fungus seem to be the final straw that kill the tree.

The articles I’ve read describe attacks on large percentages of Monterey Pines and other native pines. There are a variety of bark beetles native to northern California. Most will attack any pine they find. 

How Trees Fight Back

When attacked by the beetles the trees produce pitch, aka resin, and attempt to drown the beetle. The tree may not be able to produce enough pitch to drown all the beetles in a mass attack. When a tree is stressed, such as in a drought, it may not be able to produce much pitch at all. 

Because our bonsai are much smaller I suspect they are more easily killed than trees in forests. 

Prevention, Not Treatment

I found references to two different types of airborne fungui that are attacking pines. They are Heterobasidion annosum and Fusarium circinatum. The references I’ve found say there is no treatment once the fungus has become established.

To prevent bark beetles from attacking your trees and bringing a fungus inside the wood you need to spray with an insecticide or use a systemic like Bayer All-in-One. There are a few variations of these products, including liquid and pellets. Rose & Flower All-in-One combines a low nitrogen fertilizer with neonicotinoid insecticide and a fungicide. The insecticide is supposed to kill beetles and other boring insects while the fungicide attacks the fungus infection. 

The advice is to sprinkle a couple of tablespoons of the pellet version on top of your soil and then water. You’ll need to add more in a month or two because by watering every day the product will quickly be disolved.

Neonicotinoids are very effective against a lot of insects, but unfortunately are implicated in the mass death of bees. No final word on this yet, but it’s a good idea to be careful in how widely you use this product.

Bayer All-in-One Rose and Flower Care
Bayer All-in-One Rose and Flower Care

Another recommendation is to use a spray on fungicide, such as Daconil. The bottle below produces 64 gallons! Probably more than you need! This is also available in a pre-mixed “ready to use” 32 oz. spray bottle from Home Depot.

Note, fungicide and insecticide labels warn not to apply when the weather is hot. I usually spray in the early evening after the winds have subsided and then protect from the sun for a few days by sheltering the tree under some shade.

Daconil fungicide
Daconil fungicide

If you don’t use a Daconil then you will also need an insecticide. Daconil alone isn’t sufficient because it doesn’t kill beetles. The research literature recommends two insecticides – Carbaryl, aka Sevin or pyrethroids.

Carbaryl is one of the most frequently used carbamate insecticides and widely used for the control of a variety of pests on fruit, vegetables, forage, cotton and many other crops. It prevents attacks for up to two years. It is relatively safe to mammals but is highly toxic to honey bees! 

Most pyrethroids prevent attacks for one year. We used to think were very pyrethroids were safe to use, but now there are warnings that it also is toxic to bees. I guess the we should avoid spraying the tree immediately before and during flowering season. Removing the flowers (pollen sacs) would make the tree less of interest to bees – and is recommended practice anyway.

There are a variety of different brands of pyrethoids available. GardenSafe can be found at HomeDepot and other local nurseries.

Pyrethrin insecticide
Pyrethrin insecticide

If you decided to go with Carbaryl the most widely available brand is Sevin. It is available in a concentrate form or a pre-mixed “ready to use” 32 oz. spray bottle from Home Depot, etc.

Whichever insecticide you choose, you must saturate all of the bark to prevent beetles from attacking your tree!

Sevin insecticide
Sevin insecticide

What if My Tree is Yellow Now?

If the research papers I’ve read are true there may not be any hope. But treating with the products above won’t hurt and they don’t cost a lot. So, try them. You might be in time to save your tree!

If Your Tree Dies

In case you can’t save your tree be sure to dispose of the tree and soil. The references say to burn the diseased tree. That’s often not feasible in the environment we live in. Instead you can wrap in plastic bag and dispose in the trash. Don’t put into yard waste. 

You should also sterilize the pot before reusing it. Soak it in a strong solution of bleach and then rinse. You might want to let it sit in the sun for a few days as well. Sun light is a great disinfectant.


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