Abstract: The errors caused by traditional methods in stem analysis can be signi ficant, but these methods are still used in forest measuration. Annual diameter, for instance, is averaged from those of two magnetic directions (south-north a nd east-west) pass through the pith, which is generally smaller than the actual value. In contrast, the sectional area of bark is overestimated, since it is ca lculated by subtracting the area of wood section from over-bark area without co nsidering bark splits. In this paper, new approaches were attempted to improve t he accuracy in the measurements of both tree ring width and the sectional area o f bark. To accurately measure annual diameter, two options were suggested. The f irst one was to measure the standard diameter which is identical to the real val ue, and the second one was to calculate the correction coefficient to modify the measured annual diameters which are inconsistent with those of the real values. For calculating the bark section area excluding splits, assuming there is no in ner bark which is free of crack, the present in-bark radius was interpreted as over-bark radius, rather than by subtracting the wood area from that of the ent ire disc section.

Key words: Plant ethanol extract, Pesticides, Myzus persicae, Lipaphis erysimi, Deterrent index, Interferential index of population control