Population dynamics and dispersal gradient of Aphelenchoides fragariae in ornamental nurseries

Foliar nematodes (Aphelenchoides fragariae) cause aesthetic damage and defoliation of nursery-grown woody ornamental crops. The influence of environmental factors on the population dynamics of foliar nematodes was measured at a container nursery in North Carolina in 2006 and 2007. Air temperature, relative humidity, and rainfall data were recorded each season. Symptomatic leaves were removed every 2 weeks, from May until October, from a block of 30 lantana plants (Lantana camara) naturally-infected with foliar nematodes. Leaf samples were cut into pieces and incubated in a minimal amount of deionized water at room temperature. After 2 days foliar nematodes that had emerged were counted. The population of nematodes per gram of sampled leaf tissue increased as the season progressed, reaching a peak in July of each year, before declining for the remainder of the summer. However, a second peak in the nematode population occurred in October 2007. Changes in the nematode population were positively correlated with rainfall and daily high temperatures, but had no significant correlation with average or low daily temperatures, or with relative humidity. The dispersal gradient of foliar nematodes was evaluated in an experimental nursery block by spacing healthy plants at a distance of 0 (touching), 30, or 100 cm from an A. fragariae-infected plant. Distances were maintained by re-spacing plants as needed. Plants were overhead irrigated twice daily, and five rainfall events occurred during the trial. After 11 weeks 100%, 10% and 5% of the healthy plants were infected at the 0-, 30- and 100-cm distances, respectively. Increased plant spacing between nursery blocks may effectively reduce the spread of foliar nematodes within a growing facility.