Bulb Pests

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hi im so glad to find a forum for my fav bulb! (EDIT: moved here from Galanthus pages, M)
i wanted to know when the bulb fly starts looking for bulbs to lay eggs on?
sadly i lost my wendys gold and lady elphintstone to these horrible things.
i found about 3 grey grubs under a vitrually destroyed bulb.
i think these were allready in the bulbs as none of my other were infected.
i bought both bulbs from ebay, so i informed the seller to check any bulbs they send me in the future.

all my bubls are grown in pots so i was thinking of placing a layer of fleece over the plants securely to stop the flys.
is this feasable? would this prvent the females from laying?

[mark smyth]

Hi Rob

It depends where you live. Where are you?

[mark smyth]

Thanks Rob.

If you buy snowdrops in the spring while in growth they do not have the grub inside. The grub leaves the bulb during May and pupates nearby. It emerges to fly from the end of May and earlier in the south. They time emergence to coincide with leaves that are dying back. Their dirty work is done by the end of June

[mark smyth]

If you had them last year there are probably grubs in bulbs now.

[tonyg]

Hi Rob - welcome!
Are we SURE that the grubs are Narcissus fly?  'Under the bulbs' and 'grey grubs' suggest vine weevil rather than narcissus fly.
I have experience of both Narcissus fly and Vine weevil  and your initial post left me wondering ...
Try looking both up on the net - you might find images of the grubs to help Id them. 

[mark smyth]

Narcissus fly grub in the bulb and cleaned

[Anthony Darby]

Vine weevil grubs are pure white.

[David Quinton]

Vine weevil grubs are pure white.

.....and pure evil! The little blighters regularly eat their way through my strawberries, lavenders and heucheras.

[mark smyth]

how can i tell if any are infected this year?
each year i repot the bulbs with fresh soil, and also check the bulbs, any signs i need to look out for?

When do you repot? By late autumn the grub is already large and the bulb will be soft

[mark smyth]

When you repot after the bulb leaves have died back the damage is done ie the grub is already in the bulb. You can spray your bulbs with a systemic insecticide either commercial or agricultural or cover them with a fleece at the end of May. Check daily for emerged adults.

[mark smyth]

Q. Does this fly pupate above soil?
A. My guess is they pupate in May just outside of the bulb

Q. Can you recomend a brand of isectcide? (i didnt know you could treat for this pest)?
A. No. There are no recommended insecticides. I currently use a nasty that is likely to kill me also. It requies me to suit up but I dont.

Q. When does the fly stop looking for host bulbs?
A. when I kill it! but usually, in my experience, the end of June but last year they were active until July

I think it was Martin who said it's the large scale planting of daffs along road sides that hasnt helped the problem.

If Maggi is feeling bored some night maybe she can collect everything that has ever been said about the little _ _ _ _ _ _ _ and put it in one place. Only Joking Maggi.

[mark smyth]

If you have a pot of bulbs not showing any sign of growth gently poke around to look for the bulbs. If there is a large hole in the top you will know you definitely have the dreaded Narcissus fly

[tonyg]

I have had a similar experience with fly in part of my species narcissus collection.  I repot every summer and always check every bulb for firmness.  Any that do not seem completely hard are discarded.  By late summer many of the larvae are quite large and have begun to hollow out the bulb.  No matter how careful I have been I have not yet beaten the problem, as the bulbs all seem to grow well during the season I suspect outside sources for the fly.  Narcissus cultivars are planted in the city parks and were field grown within a few miles until quite recently.  The plants affected are in open sided cold frames while those in a greenhouse have been OK so far.

[mark smyth]

I get them in my greenhouse

[tonyg]

I hope that the healthy growth is a sign that I have removed all affected bulbs.  However I think that the fly returns from plants outside the collection each year and re-starts the problem.  Of course if I miss one bad bulb that may be enough. 
Good luck with your snowdrops.