Insects and mites in a greenhouse can eat your plants and cause significant damage. Pests can be carried into the greenhouse on your plants, on people, and on pets.
One way to keep pests out of your greenhouse is by screening the air intake. A thrips screen or another very fine screen can keep most insects and mites out. You should build a box so that air can flow through a larger surface area and airflow will not be restricted. Put a screen door on the box so you can hose down the screen.
If you put insect screening on the air intake, you should also have double entry doors. This will prevent the wind from blowing into the greenhouse when you open one door and letting pests in. Close one door before opening the other.
Do not grow any plant beds, potted plants, or weeds outside the greenhouse. These can allow pests to get into the greenhouse.
Caterpillars are larval butterflies or moths that hatch in greenhouses. The best way to deal with them is to keep adults out with a double entry door and a fly swatter.
Aphids, or plant lice, suck juices from plants. Most are wingless, but some have wings. The kind that live in a greenhouse depend on the type of crops being grown. You can get rid of them by using insecticides.
Several types of whiteflies can live in greenhouses. It can be helpful to identify the type you have. They are difficult to control because they reproduce quickly. You can put yellow sticky cards on plants to monitor whitefly populations.
Spider mites are very small and hard to see. They suck juices from plants and create webs like spiders. They tend to prefer cucumber and squash plants. Spider mites are related to spiders, not insects, so insecticides will not work. You need miticides to get rid of spider mites.
Adult leaf miners look like small flies. You can control them by introducing beneficial parasites. Greenhouses with concrete floors are less likely to have problems with leaf miners.
Gnats are more of a nuisance than a serious threat to your plants. They usually live in dead organic matter and may fly in your face when you are working in your greenhouse. You can control fungus gnats by introducing beneficial nematodes.
Slugs are not insects or mites. They chew on leaves at night and hide during the day, which makes them hard to find. Slugs leave a silvery trail on areas where they have crawled. They hide under dead leaves, pieces of wood, or pots. You can get rid of them by eliminating their hiding places.