Crape Murdering & Toothpicks in Spring

 In Tree Pest News

 

If you have ‘toothpicks’ on the trunks and branches of your crape myrtles this spring (or summer); especially those that have been recently topped (A), you may have a serious pest in your yard (C), if not, in your neighborhood. You should be concerned. You should take note.

Crape myrtles (Lagerstroemia indica) may be our toughest, most adaptable, pest and drought resistant, and showiest trees we have in our landscape. Exfoliating bark, blossoms that remain through summer, with a wide variety of colors, brilliant fall foliage, and mature sizes that range from 1 to 80 feet tall.  What an excellent landscape plant! So why would we allow them to be murdered (A), and actually pay so-called ‘professionals’ to commit this high crime?

Were it a quick death, we would immediately call the sheriff. But since it may take years for our trees to die from topping, we often don’t make the connection. The decline and death of crape myrtles are often blamed on pests (bugs and disease) and drought. But the worst offender does not crawl along the ground, rather, walks upright on two legs. We call them ‘lawn care custodians’, ‘landscapers’ and ‘arborists’, and we actually pay them to kill our trees!

Not only does topping destroy the structure of our trees, so that what grows back is less stable and likely to break, decay (wood rot) silently moves from the crown to the roots through the heartwood, without notice. While in may take several years to show signs, it can spread in only a few years (B). As rot moves to the outer sapwood, and then the bark, discoloration can easily be missed (blue arrow). Even large wounds often go unnoticed (yellow arrow), until your once beautiful tree dies or falls over.

You may have come to accept this barbaric practice as normal, or even love the look of ugly, topped crape myrtles that slowly die. But there is a new pest in town that loves them even more! And topping your trees is like ringing the dinner bell to them!

The Signs & Symptoms

Symptoms may include wilting, dieback, pin holes and frass (fine sawdust created by boring insects) at the base of your tree. The best sign is the toothpick-like strands of boring dust that protrude from the trunks and branches (C).

The Culprit

Your trees are likely infected with the Granulate Ambrosia Beetle (Xylosandrus crassiusculus).

How it is Spread

The first generation begins with the flight of adult beetles from the surrounding woods beginning in February and peaking in April and June. Adult female beetles bore into branches and the small trunks of trees, excavate tunnels, lay eggs and produce a brood, while also introducing an ambrosia fungus on which both adults and larvae feed. It takes about 2 months to complete one generation. We can have two or more generations in a year.

The Damage it Causes

In addition to boring damage to the wood, female beetles inoculate trees with ambrosia fungus which can block xylem vessels, and interfere with vascular transport.  They can also introduce or create entry points for pathogenic fungi such as Fusarium spp.  Infested plants often die from boring damage, ambrosia fungus, or infection by a secondary pathogen. Healthy crape myrtles may survive, but will likely loose most, if not, all of their branches.

Susceptible Species

While many species are fair game, small-trunked ornamentals such as crape myrtle, Japanese maple, flowering cherry, dogwood and redbud are especially vulnerable when stressed. Of course, if you have an outbreak, they may even attack seemingly healthy trees.

Positive ID

Experienced arborists can identify this pest, and even most tree owners or managers.

Control

1. Inspection. Have all of your ornamentals inspected by an experienced arborist. Especially, your crape myrtles, Japanese maples and fruit trees.

2. Sanitation. Once you have a positive ID (toothpicks), there is no driving them out. Some crape myrtles will die, others may survive but loose their branches (survivors will be ugly, and take years to rehabilitate). In the meantime, you have a brood tree (s) that can not only infect other crape myrtles in your yard, but in your neighborhood as well. Ambrosia beetles can and do attack and kill healthy Japanese maples (large trees can easily be appraised for 10 to 20 thousand dollars!). For the good of your other trees, as well as your neighbors’, you must contain this outbreak by destroying (burning or carting off to the landfill) all infected trees. We can make recommendations, but it will have to be you, the owner or manager, that makes the final decision.

3. Protection. Remaining ornamentals can be protected with Permethrin Pro (permethrins), and Onyx (bifenthrin) sprayed on the trunks, as well as with a soil drench. Pyrenone or PyGanic are organic (though expensive, and hard to find) alternatives.

4. Alert your near neighbors. They may already have infected trees. Even if they’re not, their trees are vulnerable. Consider alerting the neighborhood through e-mails and/or your community newsletter. Once they get a stronghold in a neighborhood, they’re most difficult to remove. Also, your neighbor’s infestation can revisit your yard.

5. Preventive Maintenance. Healthy trees are the best defense against future attacks. Besides adequate mulching and watering, discontinue topping. This is what likely invited this destructive pest into your neighborhood. If your crape myrtles are outgrowing their boundaries, have their crown reduced, rather than topped. This involves pruning upper leaders just beyond the branch collar of desirable lateral branches. See our Pruning Section slideshow:  http://greentreedoctor.com/pruning 

6. Replacement. Consider replacing your dead crape myrtles with varieties of suitable size. A good place to start is at our Upstate Selection Guide: http://greentreedoctor.com/selection

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