Modeling the spread of insect transmitted plant pathogens: roguing in perennial crops

Roguing (the removal of infected plants) is commonly used to manage the spread of insect-transmitted plant pathogens. In the case of perennial crops, rogued plants are often replaced with healthy plants. Replacement of infected plants has two potential benefits. First, removing an infected plant eliminates a source of inoculum, potentially slowing pathogen spread. Second, as infected plants often die or produce reduced yields, replacing an infected plant with a healthy plant may increase economic returns. The extent to which these benefits are realized depends on a number of factors. In this study, sensitivity-analyses of two spatially-explicit simulation models were used to evaluate how assumptions concerning implementation of a plant replacement program and pathogen spread interacted to affect disease suppression. In conjunction, effects of assumptions concerning yield loss associated with infection and rates of plant growth on yields were simultaneously evaluated. The first model evaluated effects of plant replacement on pathogen spread and yield on a single farm, consisting of a perennial crop monoculture. The second model evaluated effects of plant replacement on pathogen spread and yield in a 100 farm crop growing region. Results indicated that efficient replacement of infected plants combined with a high degree of coordination among farms effectively slowed pathogen spread, resulting in replacement of few plants and high yields. In contrast, inefficient replacement of infected plants or lack of coordination among farms failed to slow pathogen spread, resulting in replacement of a large numbers of plants with little yield benefit.