Vet's Best uses Peppermint Oil and Eugenol (from Clove plants) in a unique blend to kill fleas, ticks and mosquitoes. Not harmful to trees, shrubs, or flowers When used as directed, vets' best yard & kennel spray is not known to be harmful - it kills mosquitos by contact and then helps repel new ones from the area. Easy to Use Directions. Follow These 3 Simple Steps for Optimal Results: Connect to Garden Hose Connect the Made with certified natural essential oils (Certified Natural per ISO Standard 9235:2013) No Added Fragrance Non-Staining Formulas Made in the USA.