Feature Article - for release the week of November 9, 2008

Dan Culbert - Extension Horticulture Agent

 Bye-Bye Red Bays

 

A few weeks ago I received a desperate call from the property manager of Indian Hammock.  This community is located in northern Okeechobee County, and the community prides itself on maintaining natural vegetation around their homes.  Some parts are typical pine flatwoods, while others are rich hammocks with a wide variety of native plants.

 

Last July I wrote about three kinds of Bay trees found in local hammock areas.  I am afraid that soon I will have to re-write the story, as one of these outstanding trees has been found infected with a fatal fungus that clogs up the wood and is spread by bothersome boring beetles.  This is the first confirmed case of Laurel Wilt in Red Bays in Okeechobee. 

 

This Redbay tree in Okeechobee turned from green to brown in a matter of days.  Note that the leaves did not fall off, but are still attached to the branches.  Photo Dan Culbert, UF/IFAS

Splitting  infested  Redbay tree trunks show a grayish black discoloration in the outer sapwood.  Confirmation of the fungus disease is done by sending a fresh sample to a plant pathology lab where the fungus can be grown out in lab conditions.  Photo Dan Culbert, UF/IFAS

Splitting open the trunk of the Redbay tree revealed insect egg chambers and active Ambrosia beetles which help spread the Laurel Wilt fungus. Photo Dan Culbert, UF/IFAS

 

This disease has been spreading from Savannah Georgia since 2002 and has moved from there at a rate of 20 miles a year.  Forest pathologists have found that the Red Bay Wilt is closely related to the Dutch Elm Disease.  (Displaced northerners may recognize this pest which eliminated the grand old American Elm Trees that lined many city streets until the 1970s.)

 

Of concern to us in Florida is the potential extinction of the native Redbay tree (Persea borbonia), and that the disease can also infect avocado trees (Persea americana).  In fact, the first incidence of Red Bay Wilt effecting avocados just turned up recently in Vero Beach.  Other trees such as the native sassafras and exotic camphor tree may also be infected by this disease.

 

 

A fungus feeding beetle

 

The fungus is spread by very small boring beetles.  Known Ambrosia beetles, the adults are about as big as the date on a Lincoln penny. Some of these beetles are native, while others have been recently found in the US, probably hitchhiking on wood packing materials from other countries.  

 

The beetles bore into wood and create tunnels or galleries where they lay their eggs. While boring in the wood, the tunnels are infected with fungi carried in special pouches in the head.  The larvae hatch from eggs and live in the tunnels where they feed on the fungi growing in these tunnels.   These small grubs will turn into adults in a month or so.  The exit holes may be shaped like the letter-D. As they push the sawdust out the holes, a “sawdust stick” may appear on the trunk of the tree.

 

Trees that are infested with the wilt can turn from healthy green to dead brown in a matter of days.  Once the trunk is cut down, it is easy to notice the black discoloration of the outer sapwood that is caused by the fungal pathogen.

 

The local sample we collected was from a tree that turned brown in less than a week.  UF Forest Pathologist Jason Smith confirmed the presence of the fungus known as Raffaelea lauricola.    Three different non-native species of Ambrosia beetles were found, Xyleborus affinis, the Asian ambrosia beetle  (X. crassiusculus) and the Black Twig borer (X. ferrugineus).  It is curious that the insects associated with the local disease specimen were not the Redbay Ambrosia Beetle  (Xyleborus glabratus) which is often the primary vector.

 

 

Ambrosia Beetles may push out a "stick" of sawdust, a sign of infestation. Photo Dan Culbert, UF/IFAS

Here is a close-up of one of the Ambrosia beetles captured here in Okeechobee.  Photo:  Mike Thomas FDACS/DPI

See the spot above the date on this penny?  That gives you an idea of the size of the beetle. Photo: A. Mayfield, FDACS.

 

Management options

 

What to do? There has been some work on using fungicides to protect valuable urban trees from the fungal pathogen.  Other ideas are to collect and save seed from natural Redbay trees that can be grown out in disease-free areas to prevent the extinction of this species.  As for avocados, certain varieties may be showing limited resistance to the wilt diseases, but this work is in its early stage.

 

• Insect control: While some claim that the use of insecticides may be effective at killing off the beetles that spread the fungal pathogen, at this time there are no reliable treatments for prevention or control of the insect vectors. 
• Fungicide:  An experimental trial using a fungicide injected into the root-flare area of the tree has been conducted.  The process involves getting the fungicide into the tree trunk to prevent its spread.  Foliar sprays or application of chemicals for root absorption do not appear to be effective ways to get the pesticide in to the tree trunk.  The use of injections may be tried on high-value ornamental trees, but would be too expensive for use in natural areas. If persons are interested, you will need a tree service professional trained to use this method.  (If you are a tree service professional, contact our office to learn about  training.)
• Sanitation: This step is important if diseased trees are being removed. To avoid spreading the beetle and pathogen to new areas, wood or chips from infested trees should not be transported out of the local area where the trees were found. 
• Disposal:  Dead Redbay or other susceptible tree species cut in residential areas should be chipped. and left onsite as mulch, or disposed of as locally as possible.  Chipped material should be burned on site if local regulations allow it, or, it will need to be properly composted on site.  Please contact our office for details on how this composting should be accomplished.  

• The following is probably the most important rule to follow: Redbay firewood should not be transported.

 

I’ve placed more information and photos on our Okeechobee Extension web page, https://mail.ufl.edu/OWA/redir.aspx?C=923e9a6cd0c747fbb54649151f1a355c&URL=http%3a%2f%2fokeechobee.ifas.ufl.edu%2f.  If you need additional information on Laurel Wilt of Redbays and Avocados, please email us at https://mail.ufl.edu/OWA/redir.aspx?C=923e9a6cd0c747fbb54649151f1a355c&URL=mailto%3aokeechobee%40ifas.ufl.edu or call us at 863-763-6469.  Local residents can stop by our office at 458 Hwy 98 North in Okeechobee, and visit our Okeechobee County Master Gardeners from 1 to 3 PM on Tuesday afternoons.  Happy Veteran’s Day to all our Vets, and,  GO GATORS!

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Trade  names, where used, are given for the purpose of providing specific information. They do not constitute an endorsement or guarantee of products named, nor does it imply criticism of products not named. The Florida Cooperative Extension Service - Institute of Food and Agricultural Sciences is an equal opportunity/affirmative action employer authorized to provide research, educational information, and other services to individuals and institutions that function without regard to race, color, sex, age, handicap, or national origin.  Florida Cooperative Extension Service / IFAS / University of Florida.  Larry A.  Arrington, Dean. Last update: 09/16/2009.  This page is maintained by Dan Culbert