Do marigolds repel certain pests from another garden/yard plant? What are the pests and what is the plant? Thanks.

This link gives a table of companion plants and their uses.
A to Z's of Home Gardening: Companion Planting


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How to Grow Marigold Annual Flowers, Marigold Plants, Marigold Seeds at The Gardener's Network
Insect and Disease:

Insects largely avoid Marigolds. Insects do not like it's pungent odor. This is why Marigolds make good companion plants. You can even make an insect repellent spray from these plants. http://www.gardenersnet.com/spray.htm

While insects avoid Marigolds, slugs can do major damage. Slugs like to slither up the stem and chew on the leaves. They can destroy an entire flower garden of Marigolds. They can be seen on the plants overnight, in wet weather and early morning. If an infestation occurs, treat quickly to avoid major damage. http://www.gardenersnet.com//atoz/slugs.htm

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