Use of high resolution digital thermography to detect Heterodera schachtii infestation in sugar beets

Thermography is a non-destructive method used to monitor pest and disease infestations, as it is related to changes in plant water status. Surface temperature differences of the crop canopy may be an indicator of nematode infestation as the parasitation of the root system reduces evaporation of leaves. To test the potential of high resolution digital thermography to detect Heterodera schachtii infestation, experiments using increasing nematode densities and different sugar beet varieties were conducted. From June to August 2003 the crop canopy temperature was measured with a thermal infrared camera from a helicopter. A significant correlation between canopy temperature and nematode density was observed with the susceptible cultivar Monza whereas the resistant cultivar Paulina did not show any correlation. Mean temperature comparison showed significant differences between the lowest infestation level (500 eggs and larvae/100 ml soil) and the highest infestation level (>1500 eggs and larvae/100 ml soil). At the beginning of the season canopy temperature differences between healthy and nematode infested sugar beets were higher (approximately 1 degree C) compared to later assessment dates when the water supply in the soil was limited. Since low and high nematode infestation could be clearly distinguished with the susceptible cultivar by airborne thermal images, thermography might be a useful tool for monitoring sugar beet fields.