Laurel Wilt Research Articles

Searching for laurel wilt resistance in avocados of Mexican and Mexican-Guatemalan ancestry.

Laurel wilt (LW), a lethal vascular disease caused by the ambrosia fungus Harringtonia lauricola, has severely reduced avocado (Persea americana Mill.) production in Florida and decimated populations of native lauraceous trees across twelve U.S. states. All commercial avocado cultivars evaluated to date succumb to the disease, but the speed at which the tree declines varies. Cultivars with West Indian (WI) genetic background develop severe symptoms faster than those with Mexican (M) and Guatemalan (G) pedigree. Genetic resistance to LW is urgently needed, as management relies on costly cultural practices. We screened non-commercial open-pollinated progenies from 19 Mexican and 6 Mexican x Guatemalan accessions, and 2 Guatemalan x West Indian cultivars recognized as tolerant by growers. From the five disease response parameters evaluated, the final disease intensity index and disease severity on the last evaluation day were used to classify genotypes. A wide variability of responses was observed within and among families. Symptomatic plants were present in all families, while some individuals within 15 families remained asymptomatic. 'Colín V-33' (M×G) family was identified as tolerant, and Libres 3 (M), Bladimiro M-06 (M) 'Colinmex' (M×G), 'Collinson' (G×WI), Libres 5 (M) and Rag-13 (M) families were classified as moderately tolerant. This is the first-time tolerance to laurel wilt in avocado is formally reported, though surviving material needs to be propagated for response validation and field testing. Identifying tolerant accessions can help understand the underlying mechanisms and provide breeders with genetic resources for the future incorporation of resistance genes into commercial cultivars.

A Synoptic Review of Plant Disease Epidemics and Outbreaks Published in 2022.

This scientometric study reviews the scientific literature and CABI distribution records published in 2022 to find evidence of major disease outbreaks and first reports of pathogens in new locations or on new hosts. This is the second time we have done this, and this study builds on our work documenting and analyzing reports from 2021. Pathogens with three or more articles identified in 2022 literature were Xylella fastidiosa, Bursaphelenchus xylophilus, Meloidogyne species complexes, 'Candidatus Liberibacter asiaticus', Raffaelea lauricola, Fusarium oxysporum formae specialis, and Puccinia graminis f. sp. tritici. Our review of CABI distribution records found 29 pathogens with confirmed first reports in 2022. Pathogens with four or more first reports were Meloidogyne species complexes, Pantoea ananatis, grapevine red globe virus, and Thekopsora minima. Analysis of the proportion of new distribution records from 2022 indicated that grapevine red globe virus, sweet potato chlorotic stunt virus, and 'Ca. Phytoplasma vitis' may have been actively spreading. As we saw last year, there was little overlap between the pathogens identified by reviewing scientific literature versus distribution records. We hypothesize that this lack of concordance is because of the unavoidable lag between first reports of the type reported in the CABI database of a pathogen in a new location and any subsequent major disease outbreaks being reported in the scientific literature, particularly because the latter depends on the journal policy on types of papers to be considered, whether the affected crop is major or minor, and whether the pathogen is of current scientific interest. Strikingly, too, there was also no overlap between species assessed to be actively spreading in this year's study and those identified last year. We hypothesize that this is because of inconsistencies in sampling coverage and effort over time and delays between the first arrival of a pathogen in a new location and its first report, particularly for certain classes of pathogens causing only minor or non-economically damaging symptoms, which may have been endemic for some time before being reported. In general, introduction of new pathogens and outbreaks of extant pathogens threaten food security and ecosystem services. Continued monitoring of these threats is essential to support phytosanitary measures intended to prevent pathogen introductions and management of threats within a country.

Emerging pest threats to Litsea deccanensis gamble: implications for conservation and management in the Western Ghats, India

Litsea deccanensis Gamble, a vital wet-season blooming tree in the Lauraceae family, faces a dual threat from the Redbay ambrosia beetle (Xyleborus glabratus) and the Molytinae weevil (Alcidodes porrectirostris). This study, conducted in the Western Ghats, India, explores the impact of these pests on L. deccanensis, a commercially significant species used in agarbatti production. Stem bark exploitation, coupled with laurel wilt disease, contributes to the tree's declining population. These stem borers cause considerable damage to both seedlings and young saplings, and their influence extends to infestations in mature trees. The Molytinae weevils primarily target seeds, posing a significant challenge for the storage and production of planting stock. This dual pest threat jeopardizes the natural regeneration of L. deccanensis, contributing to population decline in the wild. Recognizing the urgent need for conservation, this study marks a crucial step in developing proactive strategies to manage L. deccanensis effectively within its natural habitat, safeguarding this commercially valuable species from further decline.

The Redbay Ambrosia Beetle and Laurel Wilt

The redbay ambrosia beetle, harmless in its native Asia, has become a formidable pest since its introduction to the United States in 2002. The beetle spreads the fungus Harringtonia lauricola, a lethal pathogen of North American Lauraceae trees, including avocados. The fungus infection triggers a rapid onset of laurel wilt disease, which has nearly eliminated laurel trees across the southeastern United States within a few years. The beetle has spread across nearly 300 counties in the Southeast, facilitated by trade in wood products. Effective control in natural environments remains an unresolved challenge; in avocado groves, infected trees must be removed and destroyed. Introduction of X. glabratus into Mexico, California, Central America, or South America, regions with substantial avocado industries and diverse native Lauraceae species, would be disastrous. International cooperation is necessary to address this threat.

Redbay (Persea borbonia L. Spreng) Seedling and Sapling Growth and Recruitment Near Trees with and without Putative Resistance to Laurel Wilt Disease

Laurel wilt, a fungal disease (Harringtonia lauricola T.C. Harr., Fraedrich and Aghayeva) spread by the Asian redbay ambrosia beetle [Xyleborus glabratus Eichhoff (Coleoptera: Curculionidae: Scolytinae)], presents an imminent threat to North American members of the Lauraceae family, having caused extensive mortality in several species, especially redbay (Persea borbonia L. Spreng). Varying levels of disease resistance have been recorded in redbay under controlled conditions. To investigate if previously monitored putatively resistant field redbays have influenced the regeneration and survival of conspecifics within the surrounding 0.08 ha, a survey was conducted in 2018-19 and compared to similar data collected years prior (2008-09, 2013) along the coasts of Florida, Georgia, and South Carolina, United States. Plots were originally established at six disease-infested study sites around large redbay (>7.5-cm diameter at breast height (1.37 m) (DBH)) that had survived the initial laurel wilt disease epidemic that began in approximately 2007. In 2018-19, a subset of 61 plots within 16 m of the original “survivor” redbay were recorded and compared to previous surveys. Among the original redbay selected for resistance, 22 of 61 (36%) survivors across all sites were alive in 2018 with survival rates varying from 0 to 70% between survey periods (average mortality 3.6%/year). Trees that died in years since 2008-09 had their plots reclassified as susceptible or “suscepts”. Changes in mean quadratic diameter at 1.37 m of redbay plots near survivors were significantly greater than those near suscepts, and in 2018-19, the average diameter of redbay near survivors was 7.62 cm vs. 4.90 cm for suscepts. The diameter distribution of dead and live redbay in the whole population showed a decrease in live individuals surviving past 8 cm DBH in 2018–2019, but 20 of 22 survivor candidate trees were larger than 8 cm DBH. Regeneration was occurring both clonally and sexually and tended to be greater near suscepts, but midstory resprouts per hectare and understory seedlings interacted significantly with the site and the latter differed between sites. These findings indicate that redbay is regenerating in these ecosystems, and disease resistance may allow for increased average tree size for some individuals, but an upper size threshold of around 8 cm DBH may still exist for much of the population. In addition, the importance of site variables in regeneration was apparent, making either local genetic or environmental effects an important topic for future research. Continuing to monitor these survivors while locating new candidates for disease screenings and breeding, preventing the introductions of new strains of H. lauricola, shedding light on the nature of resistance and its heritability, and initiating outplanting trials with resistant germplasm are instrumental steps in bringing redbay back to prominence in its historical range.

Impact of laurel wilt on the avocado germplasm collection at the United States Department of Agriculture, Agricultural Research Service, Subtropical Horticulture Research Station

Abstract In late 2020, laurel wilt impacted the avocado collection at the United States Department of Agriculture, Agricultural Research Service, National Clonal Germplasm Repository, Subtropical Horticulture Research Station in Miami, Florida. Monitoring of the ambrosia beetle (Coleoptera: Curculionidae) community over the next 18 months suggested that the primary vector, Xyleborus glabratus Eichhoff, was likely not responsible for spreading the fungal pathogen (Harringtonia lauricola [T.C. Harr., Fraerich & Aghayeva] Z.W. de Beer & M. Procter; Ophiostomatales). Rather, eight secondary vectors were detected in greater numbers, with Xyleborinus saxesenii (Ratzeburg) being the most abundant. After detection of laurel wilt, beetle numbers increased for 2–4 months, then gradually declined over the next year. This pest suppression was likely due to several countermeasures, including the prompt removal of infected trees and prophylactic macroinfusions with propiconazole fungicides. In addition, to preserve the genetic diversity of the Miami avocado germplasm, the Subtropical Horticulture Research Station is collaborating with other Agricultural Research Service facilities to establish backup collections at alternative locations free of the laurel wilt pathogen and its beetle vectors.

Insights into the complexities of fungus‐insect‐plant interaction: The laurel wilt disease

AbstractLaurel wilt disease, caused by the fungus Harringtonia lauricola and transmitted by the ambrosia beetle Xyleborus glabratus, poses a significant ecological and economic threat to various species of the Lauraceae family, particularly avocado. The disease is characterized by the formation of tyloses blocking xylem vessels, hindering water conductance, and decreasing leaf gas exchange. The relationship between the fungus and the beetle is complex and not fully understood, which can be described, in general, as ambrosial symbiosis depending on the habitat. The secretome of the pathogen includes hydrolytic enzymes that aid in colonization and resistance of host defence. This paper reviews the current understanding of the causes, impacts, and management strategies for laurel wilt disease. Also, it provides an overview of the complex relationship between the fungal pathogen and its beetle vector and explores the various virulence factors and secretome of H. lauricola that contribute to the aggressive nature of the disease. Moreover, this review states the ecological and economic impacts of laurel wilt, particularly on ecologically and economically valuable plants such as avocado. Current management strategies for controlling the disease, including the use of insecticides, fungicides, and biological control methods, are reviewed. Finally, we highlight some critical key points in ambrosia symbiosis biology that are of importance for disease control.

Characterization of Terpenoids from the Ambrosia Beetle Symbiont and Laurel Wilt Pathogen Harringtonia lauricola.

Little is known concerning terpenoids produced by members of the fungal order Ophiostomales, with the member Harringtonia lauricola having the unique lifestyle of being a beetle symbiont but potentially devastating tree pathogen. Nine known terpenoids, including six labdane diterpenoids (1-6) and three hopane triterpenes (7-9), were isolated from H. lauricola ethyl acetate (EtOAc) extracts for the first time. All compounds were tested for various in vitro bioactivities. Six compounds, 2, 4, 5, 6, 7, and 9, are described functionally. Compounds 2, 4, 5, and 9 expressed potent antiproliferative activity against the MCF-7, HepG2 and A549 cancer cell lines, with half-maximal inhibitory concentrations (IC50s) ~12.54-26.06 μM. Antimicrobial activity bioassays revealed that compounds 4, 5, and 9 exhibited substantial effects against Gram-negative bacteria (Escherichia coli and Ralstonia solanacearum) with minimum inhibitory concentration (MIC) values between 3.13 and 12.50 μg/mL. Little activity was seen towards Gram-positive bacteria for any of the compounds, whereas compounds 2, 4, 7, and 9 expressed antifungal activities (Fusarium oxysporum) with MIC values ranging from 6.25 to 25.00 μg/mL. Compounds 4, 5, and 9 also displayed free radical scavenging abilities towards 2,2-diphenyl-1-picrylhydrazyl (DPPH) and superoxide (O2-), with IC50 values of compounds 2, 4, and 6 ~3.45-14.04 μg/mL and 22.87-53.31 μg/mL towards DPPH and O2-, respectively. These data provide an insight into the biopharmaceutical potential of terpenoids from this group of fungal insect symbionts and plant pathogens.

Ecological dynamics of ambrosia beetle species in laurel wilt infected trees

Ecological dynamics of ambrosia beetle species in laurel wilt infected trees

Reevaluation of the Application Method and Efficacy of Propiconazole in Controlling Laurel Wilt in Avocado Orchards in South Florida

Propiconazole has fungistatic and fungicidal properties against Harringtonia lauricola, the causal agent of laurel wilt disease. Propiconazole injections are used by Florida, USA, farmers as a prophylactic method to manage the disease in avocado (Persea americana) trees, but its efficacy has remained questionable for more than a decade due to documented restricted mobility within the tree vascular system. This study was conducted to evaluate the absorption of propiconazole when using soil drenching as an alternative application method, assess the efficacy of propiconazole in controlling disease development when drenched or injected, and its synergistic effect on common cultural management practices used by the local farmers, such as branch removal and trunk cutting (“stumping”). To determine if propiconazole soil-drenching can provide better xylem coverage, potted and mature orchard trees were treated with different concentrations and artificially inoculated with the pathogen. Propiconazole translocation from the roots to above-the-ground tissue was confirmed in potted and orchard trees, but the concentrations in orchard trees were below the fungicidal threshold (1 ppm). Although none of the potted trees developed laurel wilt symptoms, all inoculated branches of the orchard trees did. Furthermore, noninoculated branches in more than 80% of the inoculated and propiconazole-treated orchard trees developed symptoms, even though the inoculated branch was cut at the early stages of disease development. To elucidate if propiconazole injections effectively control the disease, trees from a commercial orchard that were injected five times were challenged by artificial inoculation. Propiconazole concentration in trees was highly variable (ranging from < 0.01 to 294 ppm), but even in trees with a high concentration of propiconazole, inoculated and noninoculated branches developed symptoms. Even though drenched and injected trees were “stumped” soon after symptoms appeared in the noninoculated branches (4 to 5 months after inoculation), all of the stumps in the drenched plot and 80% of the injected trees, showed internal symptoms 5 and 4 months after the cut, respectively. Results demonstrate that the soil-drenching of propiconazole is an ineffective application method in orchard trees, and that the conventional injection does not prevent disease development after artificial inoculation. Moreover, because propiconazole does not prevent the movement of the pathogen to the trunk, the “stumping” of infected trees to reduce the disease in the orchard is an inadequate practice. This study highlights the critical need for other active ingredients with lower fungicidal thresholds, longer half-life, and higher xylem mobility.

Presence of the causal agent of laurel wilt disease in sassafras-associated insects.

Laurel wilt disease (LWD) is a lethal vascular wilt caused by an exotic ambrosia beetle-fungal complex, the redbay ambrosia beetle, Xyleborus glabratus Eichhoff, and its nutritional symbiont, Harringtonia lauricola (Harr., Fraedrich & Aghayeva) de Beer & Procter. LWD is responsible for the widespread mortality of redbay, Persea borbonia (L.) Spreng., devastating coastal forests in the southeast United States. More recently, LWD is causing mortality of understory sassafras, Sassafras albidum (Nutt.) Nees, in deciduous forests in Kentucky, USA; the biology, epidemiology, and long-term impacts of LWD in deciduous forests are unclear. All North American lauraceous species evaluated have shown susceptibility, and numerous additional ambrosia beetles have demonstrated vector potential, but no studies to date have assessed the presence of H. lauricola in other insects associated with LWD-infected sassafras. We sampled infected sassafras from the leading edge of the LWD range and collected insect associates to evaluate phoretic and internal presence of H. lauricola. We recorded 118 individuals of 38 morphospecies emerging; most were Coleoptera. Of the 48 specimens evaluated for H. lauricola, none tested positive for phoretic presence, but internal presence was evident in the granulate ambrosia beetle, Xylosandrus crassiusculus Motschulsky, and in a hidden snout weevil, Apteromechus ferratus Say. This is the first report of H. lauricola associated with a non-ambrosia beetle and expands our understanding of the vector potential of additional insect species while confirming the role of the granulate ambrosia beetle. These findings contribute to our understanding of LWD epidemiology in sassafras hosts from more northerly latitudes.

A New Repellent for Redbay Ambrosia Beetle (Coleoptera: Curculionidae: Scolytinae), Primary Vector of the Mycopathogen That Causes Laurel Wilt.

The redbay ambrosia beetle, Xyleborus glabratus, was detected in Georgia, USA, in 2002 and has since spread to 11 additional states. This wood-boring weevil carries a symbiotic fungus, Harringtonia lauricola, that causes laurel wilt, a lethal disease of trees in the Lauraceae family. Native ambrosia beetles that breed in infected trees can acquire H. lauricola and contribute to the spread of laurel wilt. Since 2002, laurel wilt has devastated native Persea species in coastal forests and has killed an estimated 200,000 avocado trees in Florida. Since laurel wilt is difficult to manage once it has entered a susceptible agrosystem, this study evaluated piperitone as a candidate repellent to deter attacks by X. glabratus and other ambrosia beetles. Additionally, piperitone was compared to the known repellent verbenone as a potential cost-effective alternative. The repellent efficacy was determined by comparing captures in traps baited with commercial beetle lures containing α-copaene versus captures in traps baited with lures plus a repellent. In parallel 10-week field tests, the addition of piperitone reduced the captures of X. glabratus in α-copaene-baited traps by 90%; however, there was no significant reduction in the captures of native ambrosia beetles in ethanol-baited traps. In two replicate 10-week comparative tests, piperitone and verbenone both reduced X. glabratus captures by 68-90%, with longevity over the full 10 weeks. This study identifies piperitone as a new X. glabratus repellent with potential for pest management.

Antifungal and Insecticidal Activities of Selected Plant Species from Cloud Forest of Veracruz, Mexico: A contribution to the search of novel control agents against Ambrosia pest complexes.

The antifungal and insecticidal activities of 34 extracts from 27 plant species were evaluated against fungal phytopathogens of the genusFusariumandXyleborusScolytine ambrosia beetles involved in Fusarium dieback (FD) and laurel wilt (LW) diseases. Sixteen extracts caused mycelial growth inhibition (MGI) above 23% at 2 mg mL-1againstF. solani, those fromS. nudumandM. argyrophyllaexhibited the highest MGI (57% and 49%, respectively). Thirteen extracts displayed significant antifungal activity againstF. kuroshium, those fromC. nocturnumandM. argyrophyllaexhibited the highest MGI (100% and 54.9%, respectively). Additionally, ten plants extracts caused mortality in at least one of the beetle species tested, mainly from Solanaceae species. In the most active species, 39 phenolics were identified that may have contributed to their biological effects. This study is one of the first to report the potential of plant-derived natural products against the causative agents of FD and LW.

Host switching by an ambrosia beetle fungal mutualist: Mycangial colonization of indigenous beetles by the invasive laurel wilt fungal pathogen.

Ambrosia beetles require their fungal symbiotic partner as their cultivated (farmed) food source in tree galleries. While most fungal-beetle partners do not kill the host trees they inhabit, since their introduction (invasion) into the United states around ~2002, the invasive beetle Xyleborus glabratus has vectored its mutualist partner (but plant pathogenic) fungus, Harringtonia lauricola, resulting in the deaths of over 300 million trees. Concerningly, indigenous beetles have been caught bearing H. lauricola. Here, we show colonization of the mycangia of the indigenous X. affinis ambrosia beetle by H. lauricola. Mycangial colonization occurred within 1 h of feeding, with similar levels seen for H. lauricola as found for the native X. affinis-R. arxii fungal partner. Fungal mycangial occupancy was stable over time and after removal of the fungal source, but showed rapid turnover when additional fungal cells were available. Microscopic visualization revealed two pre-oral mycangial pouches of ~100-200 × 25-50 μm/each, with narrow entry channels of 25-50 × 3-10 μm. Fungi within the mycangia underwent a dimorphic transition from filamentous/blastospore growth to yeast-like budding with alterations to membrane structures. These data identify the characteristics of ambrosia beetle mycangial colonization, implicating turnover as a mechanism for host switching of H. lauricola to other ambrosia beetle species.

Warm temperatures and host tree abundance explain variation in directional spread by laurel wilt.

The online version contains supplementary material available at 10.1007/s10530-023-03069-5.

First Report of Laurel Wilt Caused by Harringtonia lauricola (previously Raffaelea lauricola) on Northern Spicebush in Kentucky and Tennessee.

Laurel wilt (LW) is a vascular disease caused by the fungus Harringtonia lauricola (previously Raffaelea lauricola) and transmitted by its primary vector, the redbay ambrosia beetle (Xyleborus glabratus, RAB), both of which were first detected in the United States (US) in 2002, likely introduced from their native range in Asia (Fraedrich et al. 2008; Harrington et al. 2008). LW has since spread across the southeastern US causing the death of millions of native redbay, sassafras, silk bay, swamp bay and other native Lauraceae species (Hughes et al. 2017). Detection of LW on the deciduous understory shrub northern spicebush (Lindera benzoin) was previously reported in South Carolina (Fraedrich et al. 2016) and Louisiana (Olatinwo et al. 2021) and is hereby confirmed in Kentucky and Tennessee. Spicebush plants displaying typical LW symptoms were observed in September 2020 on a property spanning the KY/TN border (Christian Co., KY and Montgomery Co., TN). Several dense stands of spicebush exhibited leaf wilt, early fall leaf coloration, dead leaves on branches, and black streaks of discolored xylem. LW was already confirmed on sassafras in the area (Loyd et al. 2020), and there were abundant dead sassafras nearby. Ambrosia beetle boring dust was observed and callow female RABs emerged from containerized bolts of spicebush collected from the site, indicating that the vector used spicebush as a brood host. Samples of spicebush sapwood tissue collected from two symptomatic plants were plated onto CSMA (cycloheximide-streptomycin malt extract agar) medium. The cultures were grown at room temperature in ambient light, and a fungus was recovered and further transferred onto MEA (malt extract agar) and PDA (potato dextrose agar) media. The morphology of the two fungal isolates, referred to as LW415 and LW416, matched the typical white mucoid growth and ovoid conidia of H. lauricola (Harrington et al. 2008). DNA was extracted from conidia harvested from two-week-old MEA cultures using a modified method of Dreaden et al. (2014). The identity of the fungus was confirmed by performing PCR with the H. lauricola-specific microsatellite primer sets IFW and CHK (Dreaden et al. 2014, Parra et al. 2020). A positive amplification product was obtained for LW415 and LW416 for both primer sets, validating their identification as H. lauricola. To confirm pathogenicity, four spicebush seedlings (mean height 22.5 cm; mean ground line diameter 3.3 mm) were inoculated: two with H. lauricola isolate LW415 grown on PDA for two weeks at room temperature in the dark, and two were mock-inoculated with sterile PDA as a control. A scalpel was used to nick the spicebush stem at a bud about 5 cm above groundline, and a 3 mm2 agar plug was placed in the wound and wrapped with parafilm. The spicebush seedlings were maintained in a growth chamber with an average temperature of 24°C and a 15 h photoperiod. Wilt symptoms were evident on inoculated seedlings after two weeks, while the control plants remained healthy. Four weeks post-inoculation, black staining of the vascular tissue was present in the symptomatic seedlings, and a fungus matching the morphology of H. lauricola was consistently recovered, while no fungus was isolated from the control plants. These results provide additional evidence that northern spicebush populations may be threatened by LW and could serve as a reservoir for the pathogen and vector (Gramling 2010). The spread of LW and RAB on spicebush may gain importance as preferred hosts (e.g., sassafras) are killed.

In vitro efficacy of fungal endophytes and silver pyrazolate against Raffaelea lauricola, causal agent of laurel wilt of avocado

The South Florida avocado industry is being severely impacted by laurel wilt disease. Laurel wilt disease of avocado is caused by the fungal pathogen, Raffaelea lauricola (RL) and is vectored by ambrosia beetle, Xyleborus glabratus. Treatments options are limited, economically not sustainable, and require reapplication fungicides every couple of years. There is a crucial need for developing multiple modes of control using novel biological and chemical agents. The ambrosia beetle associated pathogenic fungi are known to outcompete other microorganisms by taking advantage of ethanol produced by the pathogen and the stressed tree. Endophytes, which reside inside the host plant tissue are part of the plant microbiome represent source of new potential biological control agents. In this study, three ethanol tolerant endophytic fungal species, isolated from avocado bark, were evaluated using in vitro dual culture assay and colonization tube (packed with bark/sapwood shaving) against RL. The endophytic isolates Tricoderma crissum, Tricoderma simmonsii, Lasiodiplodia theobromae were found to be highly capable of suppressing the mycelial colony growth of RL. The results suggest that combined abilities of ethanol tolerance and competitive colonization can provide useful criteria for identifying potential biocontrol agents. In vitro anti-RL activity of silver pyrazolate compound was assessed in both agar and liquid medium. Silver pyrazolate at levels of 30 and 45 ppm were found to be highly effective against RL. Further in planta research is needed to study the effects of endophytic fungal isolates and silver pyrazolate to assess their potential as additional tools for management of laurel wilt.

Are avocados toast? A framework to analyze decision-making for emerging epidemics, applied to laurel wilt

CONTEXTWhen emerging pathogens threaten global food security, collective action for disease management is key for protecting food systems. We evaluate how the informal exchange of information about epidemic and economic outcomes can influence the management decisions of individuals and the resulting epidemics, in the context of the avocado laurel wilt epidemic in south Florida. OBJECTIVESIn scenario analyses, we addressed how socioeconomic networks, laurel wilt epidemic networks, policy incentive structures, and social behaviors combine to influence (a) information exchange across this region, (b) growers' decisions about disease management, and (c) epidemic spread and yield loss. We identified the scenarios in which regional avocado health fared best. METHODSWe built an agent-based model to simulate laurel wilt epidemic expansion and establishment across south Florida over a 10-year period. The model used parameters specific to patterns observed and quantified from the laurel wilt epidemic in south Florida. Based on the locations and sizes of avocado orchards there, we simulated disease expansion and information dissemination through multilayer socioeconomic and epidemic networks and evaluated the effects of “carrot” and “stick” policy incentive structures and behaviors like “stubbornness” in decision making. Scenarios were simulated for multiple parameters across a 10-year time period, and the regional health of avocado and management decisions of growers were analyzed. RESULTS AND CONCLUSIONSIncreased social connections led to lower regional crop health due to increased exchange of information reinforcing selection of less expensive but less effective management choices. This information exchange was particularly impactful during the lag phase of epidemic expansion, when the cost of disease management outweighed the cost of disease. Managers who were resistant or “stubborn” against adopting these less expensive and less effective management strategies, particularly during the lag phase of epidemic expansion, contributed to greater regional health. In these scenarios, growers responded more to policies which penalized individuals than to policies which rewarded individuals. SIGNIFICANCEBy quantifying varying degrees of stubbornness, and how growers may weight past experiences and new information, we represented key aspects of decision making and its many influences on regional collective action in this novel agent-based model. The model demonstrates the caveats of information exchange across social networks during epidemics, and the valuable role that policy makers and informed educators can have, particularly during the lag phase of epidemic expansion. Decision makers and stakeholders must understand the influences of information exchange to overcome the challenges of collective action for crop health.

Mathematical Model of Basal Sprout Production in Vector-Borne Tree Disease

Some tree species respond to disease by producing basal sprouts from the base and root system of a dying tree, which can alter disease dynamics by altering demography. In the case of many lethal, airborne tree diseases, the production of basal sprouts can be a key contributor to population resurgence post-epidemic, but the effect in lethal, vector-borne tree diseases has not yet been studied. To determine the role of basal sprout production and secondary infection via the root system of infected parent trees in lethal, vector-borne tree diseases, we develop a stage-structured SI-X mathematical model and use laurel wilt, a vector-borne tree disease in which infected trees provide suitable material for vector reproduction, as our model system. The mathematical model shows that the production and secondary infection of basal sprouts do not affect the short-term dynamics of laurel wilt but profoundly alter the long-term dynamics of the laurel wilt epidemic. In particular, in the absence of basal sprout infection, basal sprout production yields a larger host population after disease establishment, but as secondary infection increases, the utility of basal sprouts to maintain the host population decreases. Results suggest management strategies for lethal, vector-borne diseases should depend on the ratio of the basal sprout production rate to the secondary infection rate.

Risk assessment of Hass avocado and Mexican Lauraceae for attack by redbay ambrosia beetle (Coleoptera: Curculionidae: Scolytinae)

Data available on request from the authors. Table S1. Factor loads of individual variables in PCA Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.