Question: I saw a redbud tree in a nursery which had tooth pick-like projections coming from the trunk and up and down most of the limbs. What causes that?

Answer: I fear you have witnessed the work of Asian ambrosia beetles. The Ambrosia beetle (pictured at: http://easttexasgardening.tamu.edu/industry/aabplate.html is a small, but deadly-to-trees insect, and it has the potential to be a major pest in the nursery industry all across the south. It has a wide host range of trees, mainly infesting small diameter, smooth bark sections of trees. Peach, pecan and plum orchards have been attacked, as well as nursery tree stock.

The beetles bore into the trunk, leaving tell-tale fragile spines of frass and sawdust sticking out of trunks like toothpicks (Images attached). The beetles cultivate a fungus (ambrosia) upon which the larval brood feed. Infested trees usually quickly die.

A Texas Cooperative Extension Write-up:

ASIAN AMBROSIA BEETLE ATTACKING TREES EARLY AND IN LARGE NUMBERS IN ET

Writer: Robert Burns (903) 834-6191
Source: Dr. James Robinson (903) 834-6191

EAST TEXAS -- Appearing three weeks to a month early, the Asian ambrosia beetle could wreak havoc among pecan, peach, plum and pear orchards, according to an entomologist with Texas Cooperative Extension.

Alien to Texas a decade ago, the Asian ambrosia beetle is now found in most all East Texas counties, as far south as Corpus Christi and as far west as Dallas, says an entomologist with Texas Cooperative Extension.

"Basically, it's now in about half of Texas. The beetle is known to attack more than 100 species of trees," said James Robinson, Extension entomologist based at the Texas A&M University Agricultural Research and Extension Center, Overton.

Robinson has had numerous calls from Tyler as well as reports from Wood and Marion counties about the early arrival of the beetle.

In past years, a number of East Texas pecan producers lost one hundred or more trees to the beetle.

Though less than 1/8 inch long, the Asian ambrosia beetle can kill a tree in a season. The beetle burrows into the trunks of susceptible tree species. It favors juvenile trees with trunks one- to two-inches in diameter, but will also attack mature trees. Unlike most other tree-infesting beetles, it prefers living trees over dead wood.

As the beetle burrows into the tree, it pushes a mixture of sawdust, tree sap and its own feces, called frass, out behind it. The sawdust and frass harden into a thin stick that juts out horizontally from the trunk of the tree.

Robinson says the extruded sticks are about as big around and as long as toothpicks. In fact, that's what they most resemble except they are stark white. The extruded sticks are telltale indicators of an Asian ambrosia beetle infestation, for infestations by other species of borers result in piles of dry sawdust at the base of the tree.

Asian ambrosia beetles are hosts to the ambrosia fungus. In a manner similar to some ants, the beetles "farm" the fungus to feed to their brood. Robinson speculated that the mild winter coupled with wet, humid conditions have made an ideal environment for the ambrosia fungus. More fungus means more larvae will be able to feed and mature.

It is the fungus that represents the health threat to the tree. The fungus plugs up the tree's vascular system, that collection of tiny vessels that transports water and nutrients to the plant cells.

Once a tree is infested, there are no chemical controls that will save it. A tree may be infested by a single beetle or by hundreds. For juvenile trees, one- to three-years old, the infestation most often proves fatal. Mature trees are more often likely to survive the infestation but may serve as staging base for the beetle to attack nearby younger trees.

For this reason, the general control strategy is to cut down and destroy any infested trees immediately. If local ordinances permit, burning the tree is the best way to ensure the beetles are destroyed as well. If open burning isn't permitted, and the tree is small enough, it can be ground up and composted. You may also foil the beetle's spread by burying the tree.

On trees that haven't been infested, a dursban or diazinon spray may discourage the beetle, Robinson said.

"But it's no guarantee that the beetle's spread will be stopped. Burning infested trees isn't a sure bet either, but right now it's the best control measure we've got," Robinson said.