The city has determined that the health of the elm trees is threatened by a fatal disease known as Dutch Elm disease. It has further determined that the loss of elm trees growing upon public and private property would substantially depreciate that value of property and impair the safety, good order, general welfare and convenience of the public. It is declared to be the intent of the city to control and prevent the spread of this disease and this section is intended for that purpose.
('69 Code, § 6.71, Subd. 1)