Outdoor infrared imaging for spatial and temporal thermography: A case study of necrotic versus healthy leaf areas on woody plants

The temperature of plants can be measured using infrared (IR) thermography. Despite the extensive use of IR imaging indoors, outdoor IR imaging is uncommon. We used IR imaging to compare leaf temperatures between necrotic spots and healthy areas of oriental cherry (Prunus serrulata var. spontanea), Japanese cornel (Cornus officinalis) and sawtooth oak (Quercus acutissima) in the field. There was a significant difference in the mean leaf temperatures between the necrotic spots (26.4°C) and healthy areas (25.6°C) of oriental cherry (p =.01). The mean temperatures in the necrotic spots of Japanese cornel and sawtooth oak leaves were 22.3°C and 29.6°C, respectively, which were not significantly different from the mean temperatures of the healthy areas. A consecutive, 2-day temporal leaf analysis in October 2018 revealed that the temperatures in the necrotic spots were generally higher than those in the healthy areas of the three species. The temperature difference between the spots and healthy areas (up to 1.4°C) was more pronounced at 13:00 hr in all three species on both days. These results reveal differences in the spatial and temporal thermal state across the necrotic spotted leaves. There is potential for use of outdoor IR imaging to visualize the response of trees to pathogen infection and abiotic stress.