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​Question: Over the past several years, I have started planting fruit trees and shrubs in my landscape including pears, peaches, figs and even a pomegranate. Most are doing well, but after the leaves popped out this spring on some of the youngest trees, I started seeing some these tiny white things on the trunks.  They look like "toothpicks" sticking out. My brown turkey figs are also showing some signs of damage. What is happening to all of my trees?

ambrosia beetle - hunter mcbrayer.jpg
This has been a common occurrence this spring; otherwise healthy trees beginning to wilt and die suddenly, and the toothpicks you describe.  Sometimes gardeners also report seeing sawdust on the stems.

While it seems that there is no rhyme or reason to this spree of dying trees and shrubs, I think that we can get to the bottom of things. Part of the problem lies in the colder temperatures that we experienced this winter, particularly those periods of sustained cold, less than 20 degrees here in Birmingham. Lots of trees, shrubs and herbaceous plants have suffered from the cold and experienced some dieback. 

We're also seeing another problem too.  If you are a frequent reader of this column, you'll know that happy plants are healthy plants, meaning that stressed plants are more likely to be affected by insects and disease. This problem that you described, the wilting and toothpicks, is a sign of a pest called the granulate ambrosia beetle.

The granulate ambrosia beetle, Xylosandrus crassiusculus (also known as the Asian Ambrosia Beetle) is a pest that emerges in early spring and can affect more than 100 species of trees.  As the female beetle emerges, she seeks out trees that will make a suitable habitat for her nest. After locating a tree, she begins to bore a small hole, about 1/16th an inch across. She then creates a cavity in the stem where she lays her legs and infects the cavity with the symbiotic ambrosia fungus on which the larvae feed. 

 We commonly see damage on peach, red maple, fig, hydrangea, Japanese maple and other thin barked trees and shrubs. Trees wilting after leaf out and frass tubes (digested wood that resembles toothpicks) sticking out of various points along the stem and major branches of trees are indicative of a granulate ambrosia beetle attack. We commonly see damage on newly planted or recently stressed trees (figs don't normally do well in a winter like this one past). We have seen several figs that are being attacked and even some shrubs that were pruned hard over the winter and before the late freeze this April.  While the boring injury can reduce the health of the tree, the hole can also be an entry point for pathogenic fungi to enter.  Infested plants often die from boring damage, ambrosia fungus, or infection by a secondary pathogen.

While this can be bad news for your new trees, there are some things that you can do. For the damaged fig, remove all of the dead, damaged or infested wood and burn it. Removing wood that has been attacked by ambrosia beetles can reduce the chances of other trees in the area being affected.  Figs are very hardy plants, often sprouting new shoots from the roots. Unfortunately, most of the other trees that are affected will need to be replaced. Keeping the plants healthy and hoping for a mild winter during the first year are best forms of prevention. Commercial insecticides can help prevent entry, but systemic insecticides will not eliminate these pests since they don't eat the wood. Insecticides and fungicides do little in terms of protection and even less as a cure.

I hope that you will not let this discouraged in your mission of creating an edible landscape.  This is a great way to add both beauty to your landscape and healthy food to your table.  For more information on this and other landscape pests, contact your local Extension Office.

Written by Hunter McBrayer of the Alabama Cooperative Extension System, C. Beaty Hanna Horticulture & Environmental Center, which is based at the Birmingham Botanical Gardens.


Comments

kerry smith

6/20/2014 3:57 PM
Some wood-boring insects attack plants regardless of plant health.  But some plants become more vulnerable to attack when they are under stress such as drought or unexpected temperature extremes. These plants, normally able to protect themselves by sealing off the insect damage, or just tolerating the damage, have lower defenses due to their weakened state. Stress causes some plants to have fewer resources for defense. Then the insects take advantage of this imbalance and find it easier to locate and attack the stressed plants.
A few of these insects are: long horn beetles, ambrosia beetles, clearwing moths, sawflies, and jewel beetles.