The Mayor shall have the power to enter upon any private grounds and to cause to be sprayed or otherwise treated any tree, shrub or plant infected or infested by any parasite or insect pest when it is necessary in the opinion of the Mayor to do so to prevent the breeding or scattering of any parasite or animal pest and to prevent danger therefrom to shade trees, plants and shrubbery planted in the streets, alleys, public parks and public grounds. Whenever in the opinion of the Mayor, trimming treatment or removal of any tree, plant or shrub located on private grounds is deemed prudent, the Mayor shall have power to trim, treat or remove any such tree, shrub or plant.