Onion Fly


One of my Shallots started to wilt around two weeks ago. The foliage turned an unusual light green colour and started to keel over. Over time it just continued getting worse and worse with no sign of recovery and so I thought it was about time to find out what was wrong.


As you can see here it was the only one of the bulbs to be affected in the row.


When I dug up the plant the culprit was clear; Onion Fly. The base of the Onion is beginning to rot and you can see tiny maggots (larvae) wriggling out. These eat the onion and then eventually turn into Onion flies.


You can see how tiny the larvae is in this photo. So what’s to be done? Nothing for this plant. I had to dig it up and put it in the bin. For the others I can just hope that this was an isolated case. I will be digging the soil over to see if I can see any other larvae. But they are so tiny it’s unlikely I will see them. I could use row cover or horticultural fleece over the plants to stop more females laying eggs.

Next year however I’ll be rotating my Onion bed to another part of the garden just in case it’s a problem with that particular bed. Apparently, putting sets in later in the season helps too as you can miss the first wave of flies. There are also nematodes that you can buy that will deal with this situation.

But… as I’m not a farmer and my livelihood doesn’t depend on my Onion crop, I’ll probably just hope that I can harvest most of my Onions and be happy with that.

4 Comments on “Onion Fly

  1. Hopefully you’ve caught the infestation before it’s really taken root…(excuse the pun)! Nasty little critters!!! xxx

  2. Nasty magots!
    I haven’t put my onion sets in yet as the ground is still so wet. Maybe the delay is a good thing then?

  3. Sorry to see this problem! I’ve not had onion fly problems. Cabbage flies and leaf miners (beets, chard, spinach) are more abundant in PDX.
    Row covers might be the best solution for protecting the onion crop.

  4. Well as vegetable growers, I think we will always face such mishaps, these onion flies and other pests will find their way to infect our labor of love. But you did well by being cautious and acted promptly. Looking at the pictures, I can see you have worked hard and kept the entire area pretty organized and neat.