Host density dependence and environmental factors affecting laurel wilt invasion

Abstract

Host size, density and distribution, in addition to climate, can affect the likelihood a pathogen will invade and saturate landscapes. Laurel wilt, caused by the vector-borne forest pathogen Raffaelea lauricola, has devastated populations of native Lauraceae in the Southeastern US, and continues to spread. We surveyed 87 plots in six coastal islands in South Carolina, Georgia and North Florida, and one inland site (Archbold Biological Station) in South Florida for laurel wilt-affected and non-affected individual plants belonging to the genus Persea. The coastal island sites were surveyed once in 2008 or 2009, and the inland site was surveyed eight times from 2011 to 2013. Disease incidence per plot ranged from 0% to 96%, with mean disease incidence 45% across all sites. Disease incidence was positively correlated with trunk diameter and density of hosts with trunk diameter > 5 cm, but negatively with the degree of clustering, which was highest for small trees. A recursive partitioning model indicated that higher disease incidence was associated with moderate temperatures, wider trunk diameter, lower relative humidity, and lower wind speeds. Disease progress over time at Archbold followed a Gompertz curve, plateauing at 3% in two years. The dispersal kernel for disease incidence from a focus followed a negative exponential distribution. The number of plots with diseased trees at Archbold was similar for redbay (P. borbonia) and swampbay (P. palustris), but was lower for silkbay (P. humilis). Understanding how host density, size, and diversity interact with environmental effects will help guide future risk prediction efforts.

Laurel Wilt: Current and Potential Impacts and Possibilities for Prevention and Management

“…All "redbays" appear to be highly susceptible to laurel wilt in controlled inoculation studies [12,54,55], and in the field, widespread mortality from laurel wilt has been observed in swampbay populations [56,57]. However, silkbay is thought to be restricted to the sandhills areas of central Florida and has not been as affected by the wilt as have other native Persea taxa [58]. One reason for this may be the overall smaller average diameter of silkbay compared to other Persea taxa and therefore it is less attractive to X. glabratus and less likely to be attacked by the beetle, which tends to preferentially attack larger diameter hosts [12,28,58].…”

“…However, silkbay is thought to be restricted to the sandhills areas of central Florida and has not been as affected by the wilt as have other native Persea taxa [58]. One reason for this may be the overall smaller average diameter of silkbay compared to other Persea taxa and therefore it is less attractive to X. glabratus and less likely to be attacked by the beetle, which tends to preferentially attack larger diameter hosts [12,28,58].…”