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Question

How do I get rid of fruit flies in my greenhouse organically?

Answer

First, you need to make sure that they are actually fruit flies. Fruit flies are often confused with a different insect called a fungus gnat. Fruit flies have red eyes, a round body and tend to hover or fly pretty slowly. They are slower moving while walking on the ground, too.

Fruit flies need overripe, damaged or rotting fruit in order to feed and breed. They are also known as vinegar flies, and are attracted to the smell of acetic acid (rotting fruit and vegetables). If you keep these materials out of the greenhouse, you are not likely to have fruit fly problems. Clean up damaged fruit and remove ripe fruit as soon as possible. The old baited fly trap with vinegar and a little soap works well to reduce their numbers, but you have to control the food source with good sanitation to get rid of fruit flies completely.

If your sanitation is good, and you are still seeing small files, they are likely fungus gnats. Fungus gnats are quite fast, both in the air and on the ground, are more thin bodied and do not have colored eyes.

Fungus gnats breed in the organic matter of soil mixes that are kept too wet and thus breeds molds, which the fungus gnat larvae feed upon. The solutions to control fungus gnats are to avoid overwatering plants in the greenhouse, improve drainage, and allow the potting soil to dry in between each watering.

Fungus gnats are not harmful to plants, but the conditions they like are also the same conditions that can lead to fungal and bacterial diseases.

Either fly problem is best solved by cultural techniques, rather than approved sprays.

Posted: Apr 2017
Answer By: Joe Pedretti