help help help - what is happening to my onions?

[antipodes]

yesterday I noticed that something strange was going on with my onions: some had leaves that seem to be curly, like a pig's tail. I lifted a couple and saw that the bulb was not forming properly and that the outer layers seem to be splitting.
I dissected one and found at the base a kind of reddish brown insect, a sort of little bug. see photos.
Does anyone have an idea on what this is? Will it affect the whole crop? I tried to uproot the ones that seem affected but the degree of damage is variable. Will it spread to the shallots which seem unaffected? Can it be treated? I am so annoyed as I really count on my onion crop - to make it worse some of the garlic is bolting, and it never does that!

[antipodes]

[Unwashed]

I would suspect onion fly.

[chriscross1966]

Isn't there a nematode that does that to alliums (onion eelworm, here: [url]http://www.donsgarden.co.uk/pests/357[/url).... or it could be weedkiller damage too, seems a bit early for onion fly unless they're indoors, in which case I'd put thrips in the frame too...

[antipodes]

Sorry I know that the pic is unclear, it is a small, slightly oval larvae type thing, no legs, and it is a red brown colour. Seems to be buried down at the bottom of the bulb. the scapes and outer layers of the onion seem to have been split open. They are outdorrs and were grown from sets. I have never had this problem prior to this.
Mostly I am worried about - will it spread to the garlic or shallots? and will I have to treat the soil in any way? I do rotate the crops....
thanks

[Robert_Brenchley]

That's onion fly; what you found is a pupa. The answer is either to grow the overwintering varieties (which don't store well), or to fleece spring-planted onions till they get to a decent size.

[ed dibbles]

One of the reasons sets are so popular is because they are less prone to onion fly than seed raised ones.

However no onion can be said to be fly proof or that it will attack every year. Growing them under environmesh or fleece is the totally sure answer but it's expensive and fiddly to keep in place or remove for looking after the crop.

Every year is different, for example the cold winter has meant my overwintering onions have not bolted this year, unlike last year when most did.

Such a shame when all our good work goes to feed insects rather than us.

[Digeroo]

Do you have Ikea over there.  They have brilliant net curtains which you can just drape over crops to keep the moths out.   A few plastic bottle with water in them round the edges to keep them in place.

[Tee Gee]

I don't think it is onion fly, I think it is a physiological problem.

Did it only occur on a few plants?

I think the original sett/s had two or more embryos in it and they have all decided to grow, twins,or triplets if you like, hence the splitting!

I would just pull it up and bin it!

Was the grub in all the affected plants?

Where and when did you get your sets?

Are they maincrop or Japanese type

When did you plant them out?

The curly tails means the plants have bolted which can occur  if the plants have had their growth checked / disturbed.

[cornykev]

I've had a few like that in the past and I've just put it down to a few dodgy sets. 

[antipodes]

In most of the ones I pulled up, I have found these "pupa" in them. I bought the sets from a reputable garden centre, where I always buy them. It seems to prefer the red ones, funnily enough and so far has not affected the white spring onions or the echalotes. I have been able to use the onions, sort of, but I have had to pull them all apart, cut off the rotten bits and wash them all to make sure there are no insects in them.  I am so disappointed as onion is usually a very reliable crop for me; I have never had to net them before.
Yes we do have Ikea, that is a good suggestion as their curtains as you describe only cost a few quid. I never thought of using that, cheaper than fleece!!!

SO it's a fly? I never noticed any! what period of the year does it occur? I only noticed the damage this week : there are no flower stalks though so it is not bolting.
Seems as if there has to be at least one pest! Two years ago it was pea thrips, last year sawfly caterpillars on the gooseberries and now this...

[Digeroo]

Grannyjanny put me onto the Ikea nets, I use them loads now.  They are brilliant for brassicas, the plants seem to love it underneath, I think it keeps the wind of as well.    I find they last longer
than fleece as well.  Though after a few years they go brittle.

I was worried that they would flatten the leeks, but they seem to be happy to gently push the nets upwards.

Do be careful though, once you get into Ikea finding your way out again is almost impossible.    I ordered some online, it was much better for my sanity.  After wandering round Ikea I tend to end up having a panic attack.

One pest, we have loads.  

[chriscross1966]

I've found onion fly attacking my garlic adn elephant garlic which I've got at home this year becasue of the white rot on the allotment.... will have to take the risk with white rot next year, with a bit of treatment and care I can control that, bu I lost all my leeks two years ago (at home) to this fly (I thought at the time it was leek moth, but now I think otherwise)... I've hit them with some nematodes (Nemasys Grow Your Own has an onion fly nematode) ... I think the reason our site is generally clear of them is cos it's so windy... the same goes for carrot root fly... don't seem to see it....