Assessment of chestnut ink disease spread by geostatistical methods

Chestnut ink disease of chestnut associated with the soil-borne pathogen Phytophthora cinnamomi Rands, is observed in single trees as rarefied foliage and general dieback which begins at the branch tips. These conditions can be detected by satellite images with high spatial resolution or by large format aerial photography. However, capturing those images frequently over small sampling areas is very expensive. This study presents an alternative method to evaluate chestnut health using lower cost technology: Small Format Aerial Photography (SFAP), of ground plots taken from light aircrafts. Normal colour and infrared SFAP from 2000 and 2001 were compared with on-the-ground evidence of chestnut ink disease. The spatial variability of health conditions of chestnut plots was adjusted in experimental semivariograms, using a spherical model. The spread of ink disease was then interpolated by ordinary kriging. Different vegetative conditions were detected using SFAP, in 2000 and 2001, showing, respectively, 5.6% and 11.1% of dead chestnut trees. The geostatistical interpolation of the study area (460 ha) found a critical cluster where chestnut decline had increased.