Early detection of pine wilt disease in Pinus tabuliformis in North China using a field portable spectrometer and UAV-based hyperspectral imagery

Forest Ecosystems

Table 2 Classification of infected stages

Age of the stand	Classification standard	Stages of infected trees
Age of the stand	Classification standard	Healthy	Early stage	Middle stage	Serious stage
40–50 years	Color of needles; Growth vigor; Resin secretion	Trees grow vigorously with dark green needles; resin secretes normally	Needles begin to turn yellow; resin secretion decreases and growth slows down	Most needles turn yellow brown and wilt, and the growth is obviously weak	Trees are dry, and needles are all reddish brown, but do not fall off