Onions - An Unpleasant Surprise

In early October, I needed an onion.  They were still on the curing rack so I went to the garage to grab one.  I’d been using up the Ailsa Craigs first since they don’t keep very long – only 2-3 months – but I decided to go for a Copra this time.

Seems ok on the outside, other than a tiny bit of frass
(I always seem to have some damage, so that doesn't usually set off any alarm bells)

I grabbed one and it felt as if the wrapper was surrounding air – the interior had completely rotted out.

Inside:  Nothing but air

That’s strange – I normally don’t see that until late spring when the odd one starts to decay.  I grabbed another Copra…and it was soft.  Oh oh…that’s not good.

A quick once over of the onions on the rack revealed the problem:

Not just a bit of frass...a LOT of frass

This, my friends, is leek moth damage.  Now, before I go any further, let me say that in the past, I have misidentified the pest that was attacking my onions and shallots - only this year did I come to realize my mistake.  All this time, I thought I was battling onion maggots when, in fact, leek moth was the culprit.

Seeing some damage this year was not in itself unusual - that happens every year.  What was unusual was the extent of the damage and how many onions were affected.  Many were a total loss - this is what the above onion looked like inside (Warning!  If you're squeamish, scroll down quickly!):

The "yuck" factor doesn't get much higher than this

In a way, I’m not surprised – the pegs holding down the netting on one of the onions beds (Bed #1) came off at one point giving the moths easy access.  I have no idea how long it was not secured since the loose netting was in a spot facing away from the garden.  It could easily have been that way for a week or two, especially if I was away at the time.  Although no variety was left unscathed, the Copras and Wethersfield that were in Bed #1 sustained the most damage, both in terms of the percentage of onions damaged (with Copras, it was 100%) and the extent of the damage to the individual onions.

So how did I come to realize that leek moths were to blame?  From their webbed cocoons:

Webbed cocoons - the tell-tale sigh of leek moths

The pupa of onion maggots is solid and brown but what I saw everywhere, on the onions, entangled in their roots and even on the bamboo poles of the curing rack, were dozens of webbed cocoons.  How I didn't realize this earlier I have no idea.

Knowing I'm dealing with leek moths rather than onion maggots doesn't change my main method of control, which is covering the beds with netting.  But it's always good to know what you are dealing with as each insect/disease, no matter how similar it is to others, has it's nuances.  For example, onion fly causes the most damage early in the season while leek moth does the most damage in July/August.  I harvest my onions in mid-August which is likely why I only notice the damage a few weeks later when the larva tunnel out of the onion and form their cocoons.

So here I was with a rack full of onions that had to be dealt with asap.  First things first - I went through all of the onions and set aside those that were a total loss.  These went into the burn pile since leek moth can overwinter on plant debris.

As I mentioned, the Copras were the most heavily hit - out of 73 onions, 46 were tossed.  The rest were at least partially salvageable so those were trimmed, sliced and frozen, as were all the other onions that had moderate damage.

Moderately damaged onions were trimmed,
sliced and frozen in a zip lock bag

I froze sliced onions a few years ago and it actually worked out very well.  When you toss them in a frying pan and cook them up to include in a dish, you would be hard pressed to tell the difference from fresh.

After dealing with all of the more heavily damaged onions, this is what we were left with:

Bottom tray:
Ailsa Craig & Red Wing onions; Camelot, Ambition & Golden shallots
Top, clockwise from top left:
Golden shallots, Red Wing, Jaune Paille de Vertus, Rossa di Milano

The onions/shallots in the bottom tray were set aside to use up first.  These either don't store well (Ailsa Craig) or they had minimal damage which shouldn't be an issue if they are used up within the next month or two.

The numbers for this years harvest look like this:

Note:  The damage on the Copras that were not tossed was still pretty significant
and required a lot of trimming, so I reduced the harvest #'s accordingly.

Not great, but it was more or less in line with last years harvest, which was also not a stellar onion year (the main issue in this case was yield, not damage):

The good news?  I'll have to be a bit stingy when using onions but I'll be ok until next year.  At least the average size of the Red Wing improved.  The Copra's also seemed to improve in size but the numbers may be misleading as so many of the bulbs were discarded.

This past season, I increased the amendments that I added to the allium beds but they were still rather small compared to those I've grown in the past.  The average size of the onions back in 2014 (excluding the freakishly large Ailsa Craigs), ranged from 110-119 grams (3.9-4.2 oz) which, to me, is the perfect size - not too large, not too small.

Plan for Next Year

There are a few things that can be done to help minimize or eliminate leek moth damage to allium crops.  Crop rotation - a practice I have always followed - is obviously a must.  What I have not done in the past is destroy onion/garlic debris - it has always gone in the compost.  While leek moth continues to be an issue in the garden, all the debris will now be burned.  I'm hoping this makes at least a small dent in the leek moth population.

In future, vigilance in keeping the allium beds covered will be key.  I'm actually in the process of replacing my finicky netting with cages which are sturdier and more reliable, especially in a windy area such as ours.  I'm hoping to have those in place for all the allium crops next season.

I'm going to hold the course when it comes to both the quantity and varieties grown.  Had the onions been a good size and leek moth not been an issue, I would have had more than enough onions to last until next season.

Although leek moth may contribute somewhat to the small size of the onions, I don't believe that they are the primary cause.  I suspect it's more of a cultural issue...as in an issue with how I'm growing them, not the fact that I'm Canadian ;).  I'll be saving my thoughts on that for a future post, however, as it affects other veg as well.


  1. Oh no, that's disappointing but at least you've managed to salvage some of them. I think it would have been worse if you hadn't discovered the damage now. Pesky things, there's always something out to get to your crops before you do.

    1. You're right - had I left them, there likely would have been much more rot and I may not have ended up with enough to last until next season. Every year I think that this will be the year when I solve my allium issues - but next year for SURE :)

  2. Gosh, that's too bad! Do leek moths infest ornamental alliums, too? I just added a ton of ornmentals to my garden this fall. I always plant onion sets around the perimeter of my little potager, and I don't recall seeing these guys. You have an impressive harvest in spite of the damage!

    1. They are a relatively new introduction to the pest scene in North America - they arrived in the 90's and are gradually spreading, as is usually the case with these types of pests. I saw a distribution map somewhere but can't recall where. As to whether they infest ornamentals, according to Wikipedia, they only damage edibles...good news as I am planning on planting some ornamental alliums in the near future and covering those would defeat the purpose!

  3. Oh how incredibly frustrating to go through the entire process of growing them and then whamo. I decided to not even grow onions next year other than some scallions because of downy mildew. The thought of watching the onion tops turn fuzzy and gray and then wither away is more than I can take. Good luck next year.

    1. Thanks Michelle. Frustrating is right - other than being a bit small, the onions looked downright great when I pulled them out of the soil. Little did I know that those moth buggers were having a feast inside the bulbs.

      I suppose everyone has one or two crops where the frustration is just too much and you need a LONG break before deciding to give them another go. For me, that's corn...it will be on hiatus again next year.

  4. Hi Margaret, I am so sorry about the loss of your Copra onions. It is good that you found them before any more damage done. Wondering if I could find a spot for another pot to grow onions next year! LOL I do the green ones for eating now. Nancy

    1. That's right - if I had left them any longer, I may have had very little to store. I'm still growing the perennial green onions although I didn't harvest any this year. I just covered them with mulch & hopefully they will come back next year.

  5. That is truly terrible news! I think it's bad enough to have something not grow very well, but to have the onions harvested and cured then to lose them is really sad. I hope you can prevent them for next year's crop. And thanks for the PSA, I had never heard of this pest.

    1. Leek moth is spreading rather slowly and, from my understanding, it's limited to the Northeast at this stage. Apparently it's point of entry was in Canada, which makes me feel rather guilty! I have my fingers crossed that I can have the cages built before the alliums need to go in next spring.

  6. Hi Margaret---I've never dealt with leek moth--yet another horrible pest waiting out there to harm our harvests!!
    So sorry about the loss of the Copras , which have always been the variety I grow. I've had problems the past two years with them sprouting in storage way too early (??????) but never that nasty pest. Hopefully your plans to keep them covered will take care of that issue next year. Ha--isn't that a typical gardener--NEXT YEAR WILL BE BETTER!!!
    Have a great week

    1. Oh, I'm SO happy to hear from you, Sue - I've missed you! I hope that things are running smoothly (or as smoothly as can be expected) on your end.

      Yes, every year there seems to be something new - or it's the same ol' same ol' but MUCH worse than before like our invasion of aphids this past spring/summer. As for storage, last year, mine did seem to sprout a little earlier than normal. I just chalked it up to a slightly warmer ambient temperature as we had a mild winter. And YES - next year it WILL be better...much better! And I'll be much more relaxed to boot ;)

  7. Hanging is too good for those leek moths! Plus, they're disgusting. Or they make the onions disgusting. I wonder if they infest ornamental alliums, also? Your unfortunate experience reminds me of my Great Daffodil Disaster of 2017.

    1. Your right! I'm normally quite a peaceful person but was not at all perturbed when I was trimming off the roots and cut off some of their little cocooned larva heads ;) According to Wikipedia, it seems as if the moth only infests edibles so ornamentals are safe, at this point anyhow.

  8. That’s such a shame. There’s always something to spoil things isn’t there. Do you just freeze the onions straight after slicing?

    1. Yes I do freeze them straight from slicing. After slicing, I pack them loosely in zip lock bags and then straight to the freezer. Packing loosely is key as a couple of wacks on the bag with your hand will separate the onions and you can take out as much or little as you need.

  9. Oh no. That’s such a shame. I haven’t seen the moth on my leeks or onions yet. But I’m thinking I’m going to have to put fleece over the seedlings as soon as I plant them out. What a nicsance. If you have leeks or onions and a few potatoes you have a meal. All the best for next year’s crops. Karen

    1. Thank you Karen - bed coverings are such lifesavers even though they are a bit of a pain to use. Weeding turns into a "task" when you have to take off netting or fleece, rather than simply pulling up a few weeds as you walk by the bed. Best of luck with your leeks and onions and fingers crossed you don't have to deal with those pesky moths!


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