For the potential economic impact of Xylella fastidiosa subsp. fastidiosa on wine growers’ livelihoods, we obtained the correspondent secondary data (area, yield and value of wine grapes) between 2015 and 2019 from the Food and Agriculture Organization, FAOSTAT database (www.fao.org/faostat/en/) and the Ministry of Agriculture (2017). There are no official updated data available relating to the price per ton of wine grapes at farm level. Estimates were therefore obtained from the field survey in the study area. Further, there are no quantitative data on the running production costs and additional costs of a hypothetical Xylella fastidiosa subsp. fastidiosa outbreak at vineyard level in Lebanon (Kourantidou et al. 2021). In order to quantify these costs (Table 1), given the absence of updated reliable primary data concerning the production costs in the country, and the need to construct pre-invasion and post invasion scenarios for Xylella fastidiosa subsp. fastidiosa, we collected and calculated the concerned costs through a specific field survey questionnaire (Suppl. material 9: Field survey) involving a focus group of 76 representative farmers, who are experts in vineyard production. The questionnaire has three sections. The first section collects information about the key farmer and the work-force in the vineyard farming system in the survey region. The second section collects current technical and financial data about the key grape farm (i.e. cultural practices, cultivars, production, cost of production, etc.) within the context of a normal agricultural situation without an Xylella fastidiosa subsp. fastidiosa outbreak (i.e. scenario A). The third section aims to estimate the additional costs that could be involved over a recovery period of 4 years in order to cope with a potential Xylella fastidiosa subsp. fastidiosa outbreak (i.e. scenario B). For this purpose, we selected farmers from the western area of the Beqaa Valley (Fig. 2), the central region of Lebanon, where Xylella fastidiosa subsp. fastidiosa may reasonably be expected to have the greatest potential direct economic impact. The selection of this field survey area was based on: (i) its suitable quarter summer temperatures (Suppl. material 3: Table S3) for Xylella fastidiosa subsp. fastidiosa diffusion (around 25–32 °C) as examined by Feil and Purcell (2001), and (ii) its economic importance. In fact, this region is one of Lebanon’s most important and oldest commercial wine grape production areas (El Chami and El Moujabber 2014). According to the Ministry of Agriculture (2017), out of 992 farmers (cultivating approximately 3,057 ha of wine grapes) in Lebanon, approximately 600 work in the Beqaa Valley, which has a wine grape surface area of 1,941 hectares, distributed between its main provinces: Baalbek (35%), Zahlé and West Beqaa (65%). At present, 70% of the national wine output is produced mainly by 4 Beqaa Valley wine producers (Chateau Ksara, Chateau Kefraya, Chateau Musar and Chateau Saint Thomas) from grapes grown in this valley with a heritage value. Furthermore, 50% of the region’s wine production is exported abroad.

Figure 2.

Wine grape plantations in Lebanon based on data from the Ministry of Agriculture (2017). The map highlights the importance of wine grape plantations in Zahlé and West Beqaa that were considered as a field study area in our estimation model.

We estimated the potential gross revenue losses in wine grapes based on yield losses as estimated by EFSA (2019), where the yield loss on wine grapes would oscillate between 1.2% (low impact), 2.1% (medium impact) and 8.1% (high impact). Here, we considered these 3 pressure levels in order to consider the uncertainty of results which would be influenced by winter climate unsuitability (freezing temperatures may reduce proliferation of the bacterium in the production areas, up to 1000 m above sea level), the unknown density of Xylella fastidiosa subsp. fastidiosa vectors (lack of field studies to confirm their activity, low or high abundance), the short period of effective infection (2 to 3 months starting in June) and cultural practices (vineyard irrigation, insecticide use, heavy pruning of plants, etc.) would give a lower incidence rate.

We based this estimate on the Partial Budget (PB) method (Table 2) as outlined by Soliman et al. (2010) due to: (i) its relevance for the purpose of calculating the additional costs (control costs) and the reduced farmers’ incomes (yield loss) of a potential Xylella fastidiosa subsp. fastidiosa invasion, and (ii) its simplicity, transparency of credibility of results. PB is a basic economic tool that analyzes the changes in costs and revenues due to any unplanned change, such as a pest invasion or management measures (use of insecticides, herbicides, fungicides, weed management, cultural alterations, etc.) in farming systems (MacLeod et al. 2004). Table 2 illustrates PB and Fig. 3 highlights the principal quantitative economic impact assessment methods used in PRA (Soliman et al. 2010) and the direct and indirect market impacts of an alien species invasion in a new location (De Ros et al. 2015). According to the Food and Agriculture Organization (FAO 2004), the economic impact assessment of a quarantine pest like Xylella fastidiosa subsp. fastidiosa is a fundamental component of PRA. PRA aims to outline “economic evidence helping the phytosanitary authority in each country to determine if the studied organism is a pest, whether it should be regulated, and the enhancement of any phytosanitary measures to be undertaken against it” (FAO 2007). Consequently, FAO (2007) has established an international phytosanitary standard (ISPM N°11) focusing on the qualitative (i.e. expert judgement) and quantitative approaches to conduct PRA without giving any preference for the use of either method. The qualitative scheme(s), through focus group expertise, are well structured and cost-effective but appear more subjective because they are based on the opinions of experts and there is a lack of transparency and repeatability.

Figure 3.

Overview of the direct and indirect market impacts of an alien species invasion in a new location. The diagram highlights the principal quantitative economic impact assessment methods used in pest risk analysis where the Partial Budgeting apapproach was considered in this research. The overview is based on Soliman et al. (2010) and De Ros et al. (2015).

As an ex-ante situation (i.e. absence of a hypothetical Xylella fastidiosa subsp. fastidiosa outbreak/Scenario A), the gross revenue generated by wine growers is estimated as close to US$22 million, almost 33% of which emanates from the study area. With a potential Xylella fastidiosa subsp. fastidiosa invasion (Scenario B), the estimated potential annual economic losses to wine grape growers would range from US$ 1.32 to almost 2.75 million (Table 3). Consequently, the upper potential gross revenue losses would be close to US$ 11 million for an average period of 4 years (EFSA 2019) if the infected vines were to be replaced by tolerant/resistant cultivars. If the growers will not be able to uproot and replace their infected plants, the total cultivated wine grapes will not generate any revenue and the upper potential gross revenue losses will amount to approximately US$ 82.44 million for an average grapevine life span of 30 years (EFSA 2019). These values depend on a set of factors: the average area of wine grapes (about 3,082 ha in 2015–2019, i.e. 34% of the total cultivated area of grapes in Lebanon), the average production of wine grapes (about 28,262 tons in the same period), the range of yield loss (low, medium and high), and the average price ($US734/Ton) of most cultivated Lebanese wine grape cultivars. The average price was estimated from the field survey in which Chardonnay has the highest price and Petit Verdot the lowest (Suppl. material 4: Table S4).

For this purpose, the official currency rate change (US$1 = LBP 1515, year 2019) has been used. The average running cost of wine grape production is US$ 3,824/ha/year prior to an Xylella fastidiosa subsp. fastidiosa outbreak in the study area (Table 4). In these routine conditions (Scenario A), labor costs were estimated at US$1,269 per ha per year, constituting the highest single cost (33%), followed by the hiring of machinery for plowing and spraying (32%). However, around 3% (US$110/ha per year) of production costs involve by insecticides without specific control of Xylella fastidiosa subsp. fastidiosa vectors, and almost 7% (US$264/ha per year) involve fungicides. The cost of replacing diseased plants is close to 2%, which may reflect the current good management of vineyards, limiting the impact of diseases.

However, the average additional management costs which could be involved in tackling a potential Xylella fastidiosa subsp. fastidiosa outbreak (Scenario B) at the vineyard level are approximately US$ 853/ha for the first year of the recovery period in which a high infestation rate (40%) and an upper impact on yield loss (8.1%) as shown in Table 5. 8% represents the costs of labor for eradication in terms of removal and disposal of diseased or dead vines as soon as PD appears in the vineyard, in order to control the infection rate. The physical removal of weeds under vine plants accounts for around 4%. The costs of labor for visual monitoring and inspection of vectors with a sweep net, for the spraying of chemicals, and for effective pruning at early symptom onset account for 2%, 5% and 13% of the total additional management costs, respectively. Replantation with resistant plants accounts for the greatest cost, around 33% based on an average price of US$1.70/plant and on an average density of around 2,032 plants/ha for all cultivated cultivars, in which “Merlot” cultivar presents the highest density of around 3,100 plants/ha (Suppl. material 6: Table S6). Most cultivated varieties in Lebanon are very susceptible to PD. However, replantation of varieties less susceptible to PD may affect the quality and the revenues of wine grapes. The use of additional insecticides to reduce the population of Xylella fastidiosa subsp. fastidiosa vectors (leafhoppers insects) amounts to around 8% of additional costs. It was also assumed that adjacent habitats would be sprayed in areas close to the vineyards, mainly in spring. Effective active ingredients should be used for successful control of Xylella fastidiosa subsp. fastidiosa vectors. Regarding the soil management/weeded area, the costs of additional chemicals for the removal of weeds under vine plants constitutes 5% of additional costs, while the use of traps to monitor or observe the movement of potential vectors from surrounding areas into the vineyards constitutes close to 11% of the total additional costs.

Consequently, the gross margin on wine grape production appears to be reduced from 26.33% (i.e. Xylella fastidiosa subsp. fastidiosa outbreak absent) to around 2% (i.e. Xylella fastidiosa subsp. fastidiosa outbreak present) in the first year of invasion as described in Table 6 and Table 7. Over a recovery period of 4 years, the aggregate of the additional costs would reach approximately US$2374/ha. For the same period, the aggregate amount of revenues lost due to a yield loss of 8.1% (EFSA 2019) would be about US$1672/ha. As a consequence of a potential Xylella fastidiosa subsp. fastidiosa invasion, the wine grape farming system (MacLeod et al. 2004) would suffer a loss of US$4,046/ha per 4 years as a net change in profit (Table 2). For the study area, where the total area of wine grapes is about 1,256 ha (41% of the total cultivated area), wine growers would be exposed to a loss of around US$ 5 million, while losses would amount to around US$12.4 million across the country (3,057 ha of wine grapes) for the entire recovery period of 4 years in which the price at grower level was assumed to be constant (Suppl. material 7: S7, Suppl. material 8: Table S8).

On average, Lebanon produces 83,125 tons of grapes per year from a harvested area of 9,066 ha, generating a yield of around 9 Tons/Ha in 2015–2019. In 2018, the gross production value of Lebanon’s grapes amounted to $US 120 million, representing 4% of the total value of the country’s agricultural production (FAO 2020). In the same year, the wine industry produced approximately 8 million bottles (75 cl), and exported around 2,322 tons of grapes, representing 50% of total production with an export value of $US 20.3 million (Banque du Liban et d’Outre Mer 2019). In this paper, we estimated that a hypothetical full spread of Xylella fastidiosa subsp. fastidiosa on the whole Lebanese wine grapes would lead to maximum potential gross revenue losses of almost US$ 11 million for an average recovery period of 4 years, to around US$ 82.44 million for an average grapevine life span period of 30 years in which infected plants are not replaced at all. Concerning the estimated additional management cost, the amount is US$853 per potentially infected hectare in the first year. For a recovery period of 4 years, the aggregate estimated additional cost would reach US$2374/ha, while the aggregate net change in profit would be US$-4046/ha.

The findings explored above provide a clear picture of the potential economic impact and private costs management assessments of a potential Xylella fastidiosa subsp. fastidiosa outbreak on Lebanese wine grapes. Here, we connect the observed results to the existing literature and derive some policy and private implications from our findings. Firstly, our research highlights an economic impact level of a potential Xylella fastidiosa subsp. fastidiosa outbreak in order to manage and identify the control measures to reduce the incidence rate and severity of PD on Lebanese grapevines. Previous studies papers (Soliman et al. 2010; McDermott 2013; Pratt et al. 2017; Barbet-Massin et al. 2020) also assumed the importance of the assessment of the economic impact of invasive species for sustainable policy planning and for the implementation of cost-efficient and environmentally-friendly pest management strategies (Rapicavoli et al. 2018; El Chami et al. 2020). The absence of such a study and the lack of updated and reliable primary data on the costs of production and pest control for Lebanese vineyards is a critical constraint to the design of sustainable management control to mitigate its severe impacts of an invasion pest like Xylella fastidiosa subsp. fastidiosa, which may affect a total cultivated area of around 3,000 ha of wine grapes in Lebanon. Obviously, wine growers were found ready to adopt an integrated management approach and to put into practice the additional necessary measures to limit Xylella fastidiosa subsp. fastidiosa damage, which mostly consist of the removal of diseased plants, replantation with resistant/tolerant cultivars, use of appropriate insecticides to control Xylella fastidiosa subsp. fastidiosa vectors, and soil management. Kyrkou et al. (2018) has summarized the private control strategies against Xylella fastidiosa on grapes in 2 categories: (i) prophylactic/preventive measures (i.e. “control of insect-vectors, control of non-vine host plants and vine propagation material, alteration to cropping techniques, breeding PD-resistant/tolerant Vitis vinifera, control via avirulent XYLEFA strains and control via other beneficial bacteria and fungi”) and (ii) therapeutic/curative measures (i.e. “use of bacteriophages of Xylella fastidiosa subsp. fastidiosa, use of an antagonistic bacterium Paraburkholderia phytofirmans strain PsJN, use of natural, antibacterial substances, and use of defense-stimulating compounds”). As the bacterium has high potential to spread in Lebanon through imports of infected host plants or the accidental entry of vectors, the Lebanese policy makers should keep pursuing management strategies to limit Xylella fastidiosa epidemics which may remain undetectable up until diseases like PD on grapevines become established. Further, strict policy limitations on the importation, marketing, and transport of plants from countries that are sources of Xylella fastidiosa infection are therefore essential in the management program to limit Xylella fastidiosa entry and spread. Further public control strategies to Xylella fastidiosa subsp. fastidiosa outbreak such as monitoring and inspection, certification, screen-house production, and clean (i.e. Xylella fastidiosa subsp. fastidiosa-free) propagation material (López et al. 2017) should be implemented by the competent local authorities. In addition, local public field trials strategies should be performed to determine the number and timing of spraying and the types of chemical treatments to use in Lebanese vineyards to best control Xylella fastidiosa subsp. fastidiosa vector populations. In fact, if Xylella fastidiosa subsp. fastidiosa vectors are not carefully managed, the bacterium has the potential to spread widely in the study area. Further, the lack of early PD notification (intended or unintended by growers or by the local competent authorities) and therefore, any delay in taking immediate action against this plant disease would lead to a spillover into other regions of Lebanon and Xylella fastidiosa subsp. fastidiosa would spread to other economically vulnerable crops and alternative habitats. Thus, it would probably lead to the expansion of PD across Lebanon, involving further management costs and the potential loss of local and international markets for the country’s wines as well as other crops’ value chain. Secondly, our analysis shows that the highest private additional costs will be incurred in the first year of infection due to the costs of labor for the removal and purchase of resistant/tolerant plants in order to continue or restart the production of wine grapes within a recovery period of around 4 years. Meanwhile, the analysis of the gross margin highlights that wine grape cultivation is relatively profitable in the study area. Farmers manage their vineyards well in terms of controlling insects, wine grape diseases and weeds. Thirdly, the findings are also important for wine growers and local wineries as the latter are vertically integrated in the farming system, and Lebanon is a net exporter of wines In fact, the potential replacement of the current cultivars of vines, which are mostly susceptible to Xylella fastidiosa subsp. fastidiosa, or their substitution by PD resistant cultivars, may affect the wine quality and revenues, as well as creating imbalances in supply and demand. Finally, our findings support the concept of multiple “known-on effects” as stressed by Macleod et al. (2004). Nevertheless, the technical measures outlined in this paper would probably not have critical financial consequences for the growers but would generate multiple “known-on effects” in terms of reducing the impacts for local wineries and limiting social effects (unemployment). In the case of an Xylella fastidiosa subsp. fastidiosa outbreak, local wineries will acquire grapes from other districts to encounter disruption in supply and this will involve additional transactional costs. On the other hand, a hypothetical Xylella fastidiosa subsp. fastidiosa outbreak may seriously affect the small grape producers, whose livelihoods will decrease in the context of the continuous drastic financial and economical current crisis facing the country.

Although the onset of Xylella fastidiosa epidemics is commonly followed by significant economic losses (Rapicavoli et al. 2018), few previous studies have estimated the annual control costs of Xylella fastidiosa outbreaks. In USA, annual control costs for Californian oleanders were estimated at US$125.0 million (Henry et al. 1997) and at US$104.0 million for grapevines across 346,000 ha of grapes in California (Tumber et al. 2014; California Department of Food and Agriculture 2018). The total cost of PD attacking grapevines was estimated at almost US$105 million per year (California Department of Food and Agriculture 2018). Using an evaluation model to assess PD impacts, knowing that glassy-winged sharpshooter (GWSS) is its vector in California, the total annual cost of disease control to growers has been estimated as rising by US$189 million per year (cost of replanting and chemical control), with an increase in the grape prices (Alston et al. 2013). This cost excludes the extra US$50 million spent every year on prophylactic phytosanitary measures such as insect control. In Brazil, the annual control costs of Xylella fastidiosa on oranges were estimated at US$120.0 million (International Plant Protection Convention 2017). In the absence of effective preventive biosecurity systems, Brazilian orange production has been dramatically affected by Xylella fastidiosa. Researchers have estimated an annual loss of US$120 million, corresponding to approximately 6% of total production value in 2003 (Mette et al. 2019). Nevertheless, Xylella fastidiosa infection was reduced from 37.6% to 1.3% in 6 years between 2012 and 2018 (Barros 2018), due to the successful implementation of compulsory requirements for importation of certified trees (Almeida and Nunney 2015). Recently, several studies have also been undertaken to estimate the potential economic impact of Xylella fastidiosa outbreaks: (i) the costs could vary between US$2.3 billion to US$7.9 billion over 50 years on Australian wine grapes and wineries (Australian Bureau of Agriculture and Resource Economics and Sciences 2018), (ii) annual production losses could reach €5.5 billion over 50 years on European olives (Schneider et al. 2020), and (iii) the values of grapes, olives and citrus spp. production losses have been estimated at around US$10.0 million, US$218.35 million and US$1.0 billion on grapes, citrus spp. and olives respectively in nine countries in the MENA region (Cardone et al. 2021). Besides, this pathogen could also affect ecosystem services by damaging rural landscapes, such as Italy’s impressive olive orchards, for which the average socio-ecological value of loss has been estimated at between €1,017 and €1,059 per ha (Frem et al. 2021).

The results explored here underestimate the potential impacts of Xylella fastidiosa subsp. fastidiosa in Lebanon. Indeed, they represent a fraction of the real potential costs if Xylella fastidiosa subsp. fastidiosa invades the full territory of the country. Important limits of this research include its assessment of one crop, one region, reliance on direct market impact, missing the indirect market impact and non-market impact of a hypothetical Xylella fastidiosa invasion in the country. The main reason of these limitations was the lack of reliable, accurate and updated specific data in the country. Future studies, based on other quantitative economic impact assessment methods (as illustrated in Fig. 2), could use enough resources, generate the requested information and try to assess the indirect market impact of a hypothetical or real Xylella fastidiosa invasion at: (i) one single-sector level (effects of Xylella fastidiosa on product prices, social welfare, consumer surplus, production surplus, trade), (ii) multiple sectors level (effects of Xylella fastidiosa on output, income, employment) and/or, (iii) entire economy level (effects of Xylella fastidiosa on income, employment and social welfare). In addition, Xylella fastidiosa may also affect seriously other valuable Lebanese economically crops (Citrus spp. stone fruits, olives, etc.) and the entire Lebanese landscape ecosystem (forest and urban trees). As such, the present research, with more specific field surveys, could be extended to include the non-market impact/costs of a potential or real Xylella fastidiosa invasion on the ecosystem (provisioning, regulating and cultural services as highlighted in Fig. 2), in the study area and/or in other locations of the country in which the bacterium could lead to serious outbreaks under specific conditions, such as the climate (mainly the quarter summer temperature – Bio10) and habitat (crops, urban ornamental plants and forests) that favor the establishment and spread of Xylella fastidiosa (Frem et al. 2020). The discrete choice experiment method would be useful for this purpose.