Tuesday, May 10, 2011

Laurel Wilt Disease Update

The latest update from Dr. Jonathan H. Crane, Tropical Fruit Crop Specialist and Jason A. Smith, Forest Pathologist/Forest Health Extension Specialist regarding Detection and Recommendations for Mitigation of Laurel Wilt Disease on Native Trees in Urban Landscapes and Avocado Trees in the Home Landscape


Tentative recommended control measures for urban and rural residents with host trees (e.g., redbay, swampbay and avocado) in the home landscape
Rural and urban residents should be on the look-out for redbay, swampbay and other host trees including avocado) showing signs of rapid wilting, dieback, and insect boring, and should report this to the Division of Plant Industry (1-888-397-1517) and/or your local forester through the Division of Forestry (http://www.fl-dof.com/ ). This will help regulatory agencies and scientists track the movement of this pest. Preliminarily, redbay ambrosia beetle attacks of redbay appear to be highest from June through October. We can expect attacks on other Laurel Family species (e.g., swampbay and avocado) to increase during the summer as well.

Control options for urban landscapes with redbay trees.
Certain high-value redbay trees can be treated for prevention of laurel wilt by use of systemic fungicides. Propiconazole (trade name Alamo®) is currently being used with some success to protect high-value redbay landscape trees. In general, the process involves mass diffusion of diluted fungicide using passive uptake. In some cases, microinjectors are being used. Research has shown that protection lasts for up to 2 years at most. For more information on propiconazole use see:
http://www.fs.fed.us/r8/foresthealth/laurelwilt/resources/pubs/laurel_wilt_isa_auf_article.pdf  
http://www.treecarescience.com/arborceuticals/fungicides/alamo

There are some landscape companies and arborists that offer a fungicide service (treatment) for redbay trees. Please be sure they are using the correct product and are certified and licensed and have insurance prior to hiring them. At present Alamo® is not registered for use on swampbay trees.  Although Merit® (imidacloprid) is registered for use on landscape and forest trees to control insects its use in areas with highly permeable soils or where surface water is present is not recommended. Furthermore, the material is highly toxic to aquatic invertebrates and bees. Unless trees are protected by a fungicide the use of an insecticide to control the redbay ambrosia beetle will not stop the progression of the disease (i.e., it is too late).

Control options for urban landscapes with avocado treesPeriodically monitor avocado trees for signs of wilting, leaf drying and browning (death), stem and limb dieback. Contact DPI if you suspect the trees to be infested with laurel wilt.

Which pest and disease control substances that are available, safe, efficacious and economic for home owners to use to either protect their avocado tree from the beetle or disease? Currently, there is no insecticide recommendation to control the redbay beetle since by the time trees show signs of laurel wilt the beetles have already infested the tree. Research is ongoing to determine which products and methods of insecticide application would be most suitable for control of the beetle in urban landscapes.  At present there is an emergency exemption for the use of the fungicide Tilt® (propiconazole) fungicide for use as a bark directed spray mixed with 2% Pentra-Bark for control of laurel wilt in avocado trees. However we do not recommend its use at this time because not enough is known about its efficacy, potential toxicity to the tree, and how long the treatment lasts. However, if Tilt® plus PentraBark is used, the mixture must be applied before the tree is infested with the disease and it has been shown to only work on trees 6-7 years old or less. This material is expensive and not readily available to home owners. People interested in treating their trees should contact a certified and licensed (including pesticide licensed) landscape or arborist company for details on applications and costs of applying this material. Read and follow the label instructions for details and safe handling.

Tree disposal of dying or dead trees
What should residents do if their tree tests positive for laurel wilt? Contact your local waste disposal service. The wood (i.e., limbs, trunk, and stems) of host landscape trees that are confirmed to be positive for the laurel wilt disease may be placed into the urban debris stream, that is, taken to the local landfill and destroyed or buried. An option is composting the tree. Current recommendations for urban and rural residents with infested avocado or native trees include: notifying DPI immediately, removing the infested tree and having it picked up by local waste management agency for disposal, or composting the tree by cutting the tree to ground, placing all wood (or chips) on top of the stump, and covering with a tarp all the way to the ground. Perhaps the composting process can be accelerated with ingredients such as topsoil, manure, fertilizer and water. For more information on how to build compost piles visit http://edis.ifas.ufl/  or go to http://edis.ifas.ufl.edu/pdffiles/EP/EP32300.pdf  and
http://edis.ifas.ufl.edu/pdffiles/HE/HE02600.pdf . Burning is not recommended because of the necessity to obtain state, county, and/or municipal burn permits and the danger of uncontrolled burning by residents.

Known hosts of laurel wilt in Florida.
Common name Scientific name
Native Redbay (Persea borbonia)
Swampbay (P. palustris)
Silkbay (P. humilis)
Pondberry (Lindera melissifolia)
Sassafras (Sassafras albidum)
Pondspice (Litsea aestivalis)
Spicebush (Lindera benzoin)
Non-native Camphor (Cinnamomum camphora)
Avocado (Persea americana)