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There are actually many ways to do this. You can make many of these remedies yourself. This collection of articles will give you more information about insect pest control, and many other helpful hints: https://www.gardeningknowhow.com/special/organic/

These are called fungus gnats. These are extremely beneficial to the soil, and harmless to your plants. Unless you actively seek and destroy these, they will be in any soil you can get. The only reason they come out is if the soil is too wet. They are a good indicator that the plant has been over watered. Otherwise, they prefer to be under the soil, and out of sight. These eat decaying matter in the soil, and help keep your plants from getting infected as easily.

If you still choose to get rid of them, you will have to provide extra fungus control to replace what the gnats are doing. You can use wettable sulfur once every few months to help control fungal infections.

Now to control the fungus gnats, you can mix rosemary oil in water and water into the soil.

Personally, I would just get some fly paper sticky traps and put them near the plants, and water less. But some people find them quite annoying so I could understand wanting to get rid of them.

My suggestion would be to use neem oil. This should be applied OUT of direct sunlight to avoid burning, though. Here is a collection of articles for more information on making your own pesticides, and other helpful articles: https://www.gardeningknowhow.com/special/organic/

This is where I go for such products: https://www.planetnatural.com/product/milky-spore-powder/

I wouldn't be able to tell you without a picture. Can you include one?

If you can apply this when you have more than 24 hours without rain, then there will be no need to reapply. If it rains right after you spray, then it may need another coat. This article will give you more information: https://www.gardeningknowhow.com/edible/fruits/fegen/dormant-oil-information.htm