Perhaps the most serious of all pests which affect the health of rubber plantations is an inanimate one, namely wind. In regions which are severely wind-swept it is useless to attempt the growth of Hevea rubber. In less exposed situations the force of the wind may be broken by leaving belts of jungle when the original clearing is carried out, or by planting rows of hardy and quick-growing trees as special wind-breaks. The idea of jungle belts has frequently been suggested as a means of checking the spread of fungus diseases, but it appears to have been very seldom carried into effect, the planter preferring to occupy the whole space at his disposal with his own proper crop. Such belts moreover possess this serious disadvantage; that if they are wide enough to prevent the passage of wind-borne fungus spores they are also large enough to afford an excellent harbourage for weeds and for many of the vertebrate enemies mentioned in the next paragraph.