Production of Conidia, selection of inoculum density, and timing the first fungicide application to manage Septoria blight of celery

Septoria blight of celery (Apium graveolens var. dulce), induced by Septoria apiicola Speg., is a destructive disease that requires fungicide applications for its management. A reliable method of inoculum production was established. Best sporulation was obtained on celery agar (CA) at a predicted optimum temperature of 22.4$ sp circ$C. A moderate inoculum density within a range of 17-35 conidia/cm$ sp2$ of leaf surface provided non-coalescing lesions necessary for rapid enumeration. Initial blight incidence thresholds of about 0.6 and 0.5% to time the first fungicide application were established based on the proportion of maximum plant weight equivalent to the cost of one fungicide application calculated plant weight and petiole number per plant, respectively, in the summers of 1990 and 1991. The IBI levels of 0 and 2% to time the first fungicide application provided non-significant results in terms of the final amount of blight and yield. (Abstract shortened by UMI.