Abstract
Aerial stem rot (ASR) is an important disease of potato worldwide and is predominantly caused by the soft rot bacteria Pectobacterium carotovorum. It differs from black leg (caused by P. atrosepticum) as it is found later in the season after row closure. The pathogen enters through wounds in the stem and expands outward leaving a distinct black lesion. Lesions spread down the stem as opposed to black leg lesions which spread up the stem from diseased tubers. Ten years of field trials were conducted using a susceptible variety in a randomized complete block design. Treatments consisted of different formulations of copper fungicides starting at row closure and continuing on a seven-day schedule until vine kill. Disease incidence and severity was rated visually, and results were used to calculate the Relative Area Under the Disease Progress Curve (RAUDPC), showing the rate of disease progress. Results showed that the RAUDPC was consistently higher in the untreated check compared to fungicide-treated plots, suggesting these products significantly reduced both disease incidence and severity. However, while the fungicides reduced disease, this did not always translate into higher yields. Nevertheless, factorial analysis of variance of yield by treatment showed significant differences in total yields with fungicide-treated plots outperforming the untreated check with yields at least 3 tonnes/ha higher. There have been few studies on the efficacy of copper fungicides for control of ASR. The findings of this ten-year study should provide growers with the data necessary to make informed decisions on the management of ASR.