Monday 4 July 2011

The dreaded Onion Fly

My poor "Jermor" shallots, planted in November and just about ready to lift, were infested with the grubs of onion fly. The first signs were a yellowing of the leaves, which is also a sign of the shallots being ready, but when I lifted a sample of the yellowest, the bulbs were rotting from the neck downwards. There were signs of little white grubs (mostly dead) and a few pupae.

Grub and pupa of onion fly

According to my gardening books, this little perisher emerges from pupae in the soil in May, but I suspect that it was earlier this year because of the warm weather. The organic treatment is netting to prevent the flies getting to the leaves, and of course growing alliums (onions, garlic, shallots, leeks) in a different place every year, cultivating the soil well so that the birds can get to the pupae.

I'm sure I have had such infestations back on the allotment, but never with the same effect. But then there was so much onion white rot that I often lost 50% or more of the harvest. Some plotholders didn't bother to grow alliums because of the losses. White rot is a fungus, and its spores can remain active in the soil for thirty years. No white rot here! It can only come in on infected sets - moral, don't plant supermarket shallots or garlic!

The grubs have not in themselves done much damage, and most of them are dead, but rot has taken hold where they have been working - just above the neck of the shallot - and unless I cook or freeze the bulbs immediately I will lose the lot. For that reason I'm making some more shallot confiture. I'd have made that anyway, but not with green shallots, so it'll be interesting to see if there's a difference.

The garlic and onions are also affected. I've lifted the garlic ("Germidour") and found tunnels and pupae, but not the rot, as yet. The garlic harvest is magnificent, with large, even-sized heads and decent-sized cloves.

The Germidour haul

The wounds caused by the grubs have scarred over, so I've hung the dried bulbs in bunches in a cool place away from the mice.


GaynorB said...

We tasted the shallot confiture you gave us at the weekend. It really was delicious!

Sorry to read about the onion fly troubles though .......

Pollygarter said...

Glad you enjoyed it. Not at all like pickled onions! Simple to make, just takes a little time.

Jean said...

Such a shame about the onion fly. Gardening is such a battle - us versus the critters. At least the drier weather means we haven't had so many slugs this year.