Onion worm control – How to get rid of onion worms

In some parts of the United States, onion worms are without a doubt the most serious pest of the onion family. They infest onions, leeks, shallots, garlic and chives. Discover the identification and control of onion worms in this article.

What are onion worms?

Onion worms are the larval form of a small gray fly that looks a lot like a common housefly, except that it is only a quarter inch long. The small cream-colored worms infest bulbs, filling them with tunnels. The damage leaves the bulbs susceptible to bacterial invasion.

Worms have about three generations each year. The first generation is the most important and causes the most damage. The last generation attacks just before harvest. This generation leaves the bulbs susceptible to rot during storage.

The parents of onion worms, which are small gray flies, are

difficult to distinguish from any other fly. Females lay their eggs on the ground where onions grow so that their young get a good start in life. When they hatch, the worms feed on the underground onion bulbs for about three weeks before leaving the bulb and moving to the ground, where they reproduce. They then emerge as adults and begin the process all over again.

How to get rid of onion worms

Damage caused by onion worms includes low germination and survival rates in young plants. Older plants may have soft, yellow leaves. Bulbs may show signs of light rot while still in the soil, but sometimes they do not begin to rot until after harvest.

Crop rotation is one of the most important aspects of onion worm control. Worms feed only on members of the onion family. If newborn worms do not find a food source, they will not survive. When thinning your plants, remove and destroy waste material, which also serves as a food source. You must also completely remove any crop residue left at the end of the year.

Insects like to pupate and overwinter in areas with large pieces of organic matter. To avoid providing them with a convenient hiding place, make sure all fertilizer is completely decomposed before adding it to onion growing areas.

Most insecticides available to hobby gardeners are ineffective. Contact insecticides never reach the worms, which are hidden in the bulbs. Insects have developed resistance to systemic insecticides.