Zinnias are rarely attacked by insects. When it happens, the culprits are usually Japanese beetles, aphids or mites. You can treat the infestation with insecticide, but be careful of chemicals that do more harm than good. You can also use the all-natural method that has proven effective for thousands of years.
You can use an insecticidal soap to prevent aphid attacks, but be sure that you are using an organic formula. Avoid using any type of harsh chemicals in your garden, as they will often be absorbed into the soil, causing unexpected problems years later.
Instead of insecticides, consider using natural enemies of the aphids and beetles that eat your zinnias. Ladybugs and praying mantis are both attractive predatory insects that can be added to your garden area if you have a problem with insects nibbling at the leaves.
Pest Repellent Plants
Marigolds are one of several common plants that are recognized for their repellent effects. Planting marigolds at intervals around the garden helps reduce the activity of many types of pests. Additionally, mint is a natural ant repellent that can be planted among your other plants, or even in your lawn, where it produces an appealing scent each time the lawn is cut.