Table C.2: Expansion rate

Overview of the results of the Expert Knowledge Elicitation (2nd EKE question)
Parameter	Expansion rate after the lag phase
Stratification	Grapevine production areas in the EU with average yearly temperature above 17°C as average of the coming 30 years.
Question	Assuming that human assisted spread between vineyards is excluded by perfect sanitary measures or prohibited exchange of tools/workers. What is the 95th percentile of the distance newly infected vineyards have to the nearest existing one already infected one year before? [m/year]
Results	P1%	P2.5%	P5%	P10%	P16.7%	P25%	P33.3%	P50%	P66.7%	P75%	P83.3%	P90%	P95%	P97.5%	P99%
Elicited values	20					135		250		500					1,000
EKE results	20.0	25.1	34.4	54.5	83.8	124	168	270	401	483	586	697	817	911	1,003
Fitted distribution	BetaGeneral (0.92036,2.6668,17,1,230)
Figure (C.2a): Comparison of elicited and fitted values/density function to describe the remaining uncertainties of the parameter							Figure (C.2b): Cumulative distribution function (CDF) of the likelihood of the parameter

Summary of the evidence used for the evaluation
In this assessment only spread by natural means is considered (movement of workers or machinery is excluded). Results on the spread rate of Xanthomonas citri pv. citri (Xcc) were reviewed (EFSA et al., 2019b), incl. Original references on spread of Xcc in Florida (Gottwald et al., 2001). Distribution and product profile of vineyards in the area under consideration (this is the EU area with average yearly temperature above 17°C as average of the coming 30 years).
Main uncertainties
Comparability of results from Xcc and Xcv regarding esp. differences in host systems (citrus orchards vs vineyards), influence of human assisted spread in the Xcc assessment. Unknown susceptibility of EU cultivars to Xcv. Pest development of Xcv under EU climatic conditions, e.g. efficacy of the number of infection cycles; esp. compared to Florida. Influence of barriers to spread between vineyards. Movement of the bacteria via droplets, plant parts during extreme weather events, esp. hail, thunderstorms.
Reasoning for a scenario which would lead to a reasonable high proportion	The judgement on the upper limit considers that Grapevine is more vulnerable against strong weather events causing wounds (points of inoculum) and contributing to the spread (e.g. wind, thunder/hail storms), than citrus. The spatial distribution and distance among vineyards in the EU do not represent a major limitation for the spread of the species.
Reasoning for a scenario which would lead to a reasonable low proportion	The judgement on the lower limit considers that High proportion of vineyards, esp. table grapes, are protected against weather events. The spatial distribution and distance among vineyards in the EU limit the spread of the species. EU grapevine production area is more extended and heterogeneous than EU citrus growing area and therefore the probability of having environmental conditions unfavourable to the fast growing of the inoculum is taken into account.
Fair estimate as judgement on the weighted evidence	The judgement on the median considers that The spread of Xcv on grapevine is greater compared to spread of Xcc on citrus.
Precision of the judgement as description of remaining uncertainties	The judgement on the interquartile range considers that High uncertainties on lower values due to the lack of reports on spatial spread. Medium uncertainties on higher values due to the possibility of extrapolation of results from Xcc.