Fully read the labels of chemicals, understand and follow their safety precautions. I would do this before you make your purchase. Whether you use this company or not you can find information about many chemicals at Do My Own
A fly that lays eggs in the soil near the base of plants, the hatched maggots eat plant roots, seeds, and stems. The heat inside a greenhouse or mini-hut can allow them to emerge before you even have your plant in the ground. You should prevent them, once you notice you have them it will probably be late, either the plant will die or be severely stunted you may grow several seasons without them being a problem but they are common to have.
Non-chemical treatment, Use Diatomaceous Earth in and on the soil to kill maggots and reduce egg-laying. Place a collar around the plants, pressed a few inches deep into the soil. Use Beneficial Nematodes (Steinernema feltiae) they can kill over 230 soil pests.