Crop diseases may be affected by landscape composition, but limited quantitative information is available. We studied the effects of landscape factors on the incidence of the psyllid-transmitted bacterium Candidatus Liberibacter solanacearum (CLso) haplotype C in carrots in Finland. Samples were collected from 104 carrot fields in 2013 and 2014. The relationship between CLso incidence and landscape data was analysed using logistic regression. The probability of CLso infection significantly increased with increasing area of carrot cultivation, up to a 10 km radius. Spruce biomass (spruce is the winter shelter of the main vector, Trioza apicalis,) within 200 m distance from the field edges affected CLso infection in landscapes with a low to medium area proportion of carrot cultivation but not in landscapes with a high proportion of carrot fields. Disease incidence was higher on clay soils than on mineral soils. The findings illustrate the importance of movement of the vector between carrot and spruce and highlight this disease as a landscape-scale disease syndrome, which needs to be managed also at the landscape level. Moderating the proportion of carrot fields in a carrot production landscape could be a key to manage the disease by breaking the epidemic cycle at the landscape level.

作物病害可能会受到景观组成的影响，但可获得的定量信息有限。我们研究了景观因素对芬兰胡萝卜中木虱传播细菌Candidatus Liberibacter solanacearum (CLso) 单倍型 C 发病率的影响。2013年和2014年从104个胡萝卜田采集样本。使用逻辑回归分析CLso发病率与景观数据之间的关系。CLso 感染的概率随着胡萝卜种植面积的增加而显着增加，最大半径可达 10 公里。云杉生物量（云杉是主要病媒Trioza apicalis 的冬季避难所，) 在距离田边 200 m 范围内，在胡萝卜种植面积比例低到中等的景观中影响 CLso 感染，但在胡萝卜种植比例高的景观中则不受影响。粘土土壤的发病率高于矿质土壤。研究结果说明了病媒在胡萝卜和云杉之间移动的重要性，并强调这种疾病是一种景观规模的疾病综合征，也需要在景观层面进行管理。调节胡萝卜生产景观中胡萝卜田的比例可能是通过在景观层面打破流行周期来控制疾病的关键。