How to Get Rid of Fleas/Ticks | The Family Handyman~ Plant oils: cedar oil/lemongrass oil evolved to protect plants from insect damage. The EPA considers cedar oil safe pesticide in low concentrations (higher concentrations can irritate skin and are toxic if ingested). Cedar oils are used in flea sprays for pets. Spraying cedar oil diluted w/water on lawn & shrubs repels insects. Colorado State University ext. cautions spray could damage sensitive plants/trees or those in drought condition.