As a step towards the realization of wireless nanosensor networks in agricultural monitoring applications, a theoretical path-loss model is proposed. This model can predict the average attenuation of THz radiation in a channel composed of air and plant leaves, given the composition of air as well as attributes of leaves such as their permitivity. In addition, a Monte Carlo-based log-distance path-loss model in the vicinity of a plant is proposed, which takes the shadow fading nature of such a channel into account. The latter model, which is based on the transmission distance, can approximate variations of THz path-loss from its mean value. Through simulation results, it is shown that the proposed log-distance/Monte Carlo- based model is in good agreement with the theoretical model.