Occurrence of symptoms of gummosis on A. decurrens
The first survey (Feb. 2015) indicated incidence of gummosis on 80 % of the trees surveyed. By Aug. 2015 (fourth survey), all the trees (100%) were found infested which indicated an increase of 20% of incidence in six months. Based on the occurrence of gummosis on different segments of the stem, the highest was on the lower stem (L) compared to the upper part (U) and stem covered by crown (S) (Figs. 7 a & b).
Over time, the mean severity of gummosis increased significantly (R2 = 0.98) from the bottom to the top of the tree which indicated that the bark beetles got settled, increased in number and they actively moved from the lower part to the upper part of the stem.