Laurel Wilt Disease and the South Florida Avocado Industry — What Arborists Need to Know
Laurel Wilt Disease and the South Florida Avocado Industry
Miami-Dade County was the largest avocado-producing county in the continental United States before Laurel Wilt Disease (Raffaelea lauricola) began spreading through the commercial groves of Homestead in the mid-2010s. The crop loss has been severe: tens of thousands of avocado trees killed, grove acreage reduced by more than half in some estimates, and a $50+ million annual crop contribution to the county economy put at risk.
For arborists and tree contractors working in South Florida — particularly in Miami-Dade's agricultural zones and in residential properties that include mature avocado trees — understanding Laurel Wilt is both a professional and regulatory obligation. FDACS requires reporting of suspected Laurel Wilt in commercial avocado settings, and arborists who handle infected wood without proper protocols can accelerate the spread.
Disease Overview: Pathogen and Vector
Laurel Wilt is caused by the fungus Raffaelea lauricola, which is vectored (transmitted) by the redbay ambrosia beetle (Xyleborus glabratus). This beetle is native to Asia and was accidentally introduced to the southeastern United States through infested shipping material, first detected in Port Wentworth, Georgia in 2002.
The infection mechanism:
- A female X. glabratus beetle bores into the bark of a susceptible host (any species in the family Lauraceae)
- The beetle inoculates the fungus into the host's xylem tissue as it excavates a brood gallery
- R. lauricola colonizes the xylem vessels, blocking water transport
- The tree wilts rapidly — crown death in 2–6 weeks from first symptom
- The beetle completes its lifecycle in the dead wood and disperses to new hosts
Why it spreads so fast: Infected wood contains both the beetle and viable R. lauricola fungus. Moving infected wood — even to a woodchipper or burn pile — can spread the disease if the wood is moved while beetles are still alive inside it. This is the primary pathway that moved the disease from forest trees into Miami-Dade's commercial avocado groves.
Impact on Miami-Dade's Avocado Industry
Miami-Dade's Redland agricultural district (south Homestead, Florida City, and surrounding areas) was home to approximately 7,000 acres of commercial avocado production as recently as 2010. Laurel Wilt began appearing in commercial groves around 2012–2014 as the disease moved south from infected wild bay trees (Persea palustris and P. borbonia) in conservation lands adjacent to agricultural areas.
By 2020, FDACS and UF/IFAS estimated that Laurel Wilt had killed trees on more than 60% of Miami-Dade's avocado acreage. Many growers abandoned infected groves rather than continuing to fight an unwinnable battle with available tools.
The economic impact extends beyond the avocado industry. Miami-Dade avocados are a significant part of the county's agricultural heritage and cultural identity, and many residential properties in the Redland area contain 20–40-year-old avocado trees that have been killed or are at risk.
Disease Stages and Visual Identification
Laurel Wilt Disease Progression in Avocado — Identification Guide for Arborists 2025
| Stage | Time from Infection | Visual Signs | Action |
|---|---|---|---|
| Early | Days 1–7 | Small beetle entry holes (1–2mm) at trunk or main scaffold. May have fine sawdust (frass). No canopy symptoms yet. | Inspect trunk and main branches. Check for frass. Sample bark at entry holes. |
| Developing | Days 7–21 | Wilting of individual branches or shoot tips. Leaves wilt but remain attached. Vascular discoloration (dark streaking) visible if bark removed. | Confirm with cross-section of sapwood — dark blue-gray streaking diagnostic for LBD. Submit sample for PCR confirmation. |
| Advanced | Days 21–42 | Crown wilt progressing rapidly — multiple branches or entire crown affected. Dead leaves clinging to plant. Dark vascular discoloration throughout sapwood. | Treatment options extremely limited at this stage. Begin removal planning. Do not move wood off-site without beetle control protocol. |
| Dead tree | Weeks 4–12 | Complete crown death. Brown, desiccated foliage. Beetles may still be active in wood for several weeks. | Remove and chip immediately OR solarize in place (see removal protocol). Report to FDACS if commercial avocado. Do not leave standing dead wood — it is an active beetle reservoir. |
PCR molecular testing is the only definitive confirmation of R. lauricola. Samples can be submitted to the UF/IFAS Plant Diagnostic Center in Gainesville or the FDACS Division of Plant Industry in Gainesville. Commercial avocado growers with suspected LBD should contact FDACS immediately. Source: UF/IFAS; FDACS; FloridaLandscapeIQ, 2025.
Arborist Protocols for LBD-Suspected Trees
Before removing suspected LBD-infected wood:
- Confirm or strongly suspect LBD based on visual signs and sapwood vascular discoloration
- If commercial avocado: contact FDACS Division of Plant Industry before removal
- Schedule removal during the cooler months when beetle activity is lower (December–March)
- Chip all wood to pieces 2" or smaller on-site immediately after removal — chipping destroys beetle galleries and fungal material
- Do not transport uncollected logs or large branch wood off-site — beetles can emerge from recently-killed wood for 4–8 weeks
- Dispose of chips by:
- Incorporating into soil as mulch (fungus and beetle die rapidly in aerobic conditions)
- Composting at the site
- Hauling only in covered trucks to a commercial composting facility
Propiconazole trunk injection (for valuable, non-symptomatic trees): UF/IFAS research has documented that propiconazole (Alamo) trunk injection in non-symptomatic, high-value avocado trees can delay or prevent LBD infection during periods of high beetle pressure. This is not a cure for symptomatic trees — it is a preventive treatment for currently healthy trees in high-risk areas. Application requires licensed pesticide applicator certification.
Current Disease Status in South Florida (2025)
Laurel Wilt is now endemic in Miami-Dade County's agricultural areas. The disease is also present in Broward and Palm Beach counties' native bay tree populations but has not established in commercial plantings at the same density as Miami-Dade.
Homestead/Redland growers have experienced the most significant losses. Some growers are trialing LBD-tolerant avocado rootstocks from UF/IFAS research programs — this is the most promising long-term management pathway but is still in research phase.
Residential avocado trees throughout South Florida, including in Miami-Dade, Broward, and Palm Beach, are at ongoing risk when located near infested wild bay populations or other infected avocados.
Find ISA-certified arborists and licensed tree contractors with LBD experience in South Florida through the FloridaLandscapeIQ Contractor Directory.
Source: UF/IFAS Laurel Wilt; USDA Forest Service; FDACS Division of Plant Industry; Ploetz et al., “Laurel Wilt, a Destructive Disease of Avocado in Florida,” Proceedings of the Florida State Horticultural Society, 2012; FloridaLandscapeIQ Staff, March 2025.