Downy mildew caused by Peronospora sparsa is considered one of the most important diseases affecting cut roses under glass in the tropic. Under favorable environmental conditions, rapid epidemics of the pathogen hard to control may cause the total loss of susceptible rose cultivars in a plantation. Disease detection is based on close inspection of plants to identify affected areas in the greenhouse. However, this method is time consuming, expensive and in most cases not suitable for the detection of initial disease symptoms. In spite of this, only limited research has been conducted to find alternative methods for the early detection of P. sparsa. Therefore, it is necessary to improve the diagnostic methods to implement timely disease control. Non-invasive sensor techniques like infrared thermography have been reported to offer a high potential for monitoring plant-pathogen interactions. The aim of this study was to investigate the ability of thermography for the detection of downy mildew symptoms on roses under controlled conditions as the first step to its subsequent use under commercial conditions. Rose leaves and detached full stems of three rose cultivars were inoculated and the development of the infection was followed by visual inspection and with thermal imaging using a camera system with 0.03 K thermal resolution. Disease symptoms on the susceptible cultivars were observed 6 days post inoculation (dpi) by visual inspection while in themograms the presence of the pathogen was observed 3 dpi. Furthermore, differences in the temperature of leaves were observed during the spread of the disease throughout the evaluation period. The results indicate that the use of thermography may be an alternative tool to detect downy mildew infection on roses in early stages also under production conditions.