They are insect eggs, which is interesting as there are very few species that can use × Cupressocyparis as food-plants. Sawflies or moths are the possible culprits, although Sawfly eggs are not usually as large or as conspicuous as these and I don't know of any moth that's known to eat × Cupressocyparis - although there are quite a few that feed on other conifers.

Compare with these eggs on a Pine:

http://www.flickr.com/photos/treeblog/3837136921/

I would let them hatch and see what they turn into - they are not of a large enough number to damage your tree.

What an interesting picture. I have never seen eggs like that on a conifer, never mind leylandii.

They do look like moth eggs, but I have no idea what kind.

Juniper shoot moth, probably, and you should probably trim off the tips to save the inevitable browning and die back in spring as a result of the caterpillars chomping their way through the soft new growth. Unless, of course, out of interest you want to preserve the moth species numbers which are probably less than Leylandii!
Phil J

Interesting. I have seen clusters of moth eggs like this on other food plants but as said above not on × Cupressocyparis or indeed any true or false cypress.

Thanks for the name of a possible candidate Phil.

Just searched for it here:

http://ukmoths.org.uk/show.php?bf=407

It seems there are two invading (non native) relatives of the Juniper Shoot Moth both of which have been recorded as feeding on × Cupressocyparis, but all three of these Argyresthia species (including the Juniper Shoot Moth itself) are micro moths - i.e. very small indeed with a 7 to 9 mm wingspan - and their eggs are inconspicuous and extremely small, only 0.5 mm long and 0.3 mm wide, which is far smaller than Dave's appear to be.

Wow, many thanks everybody for your brilliant answers. Its nice to see forum members are interested in moths as well as plants!

But I'm afraid I care about my new hedge more than the moths, since I've put a huge amount of work into keeping these tiny trees alive (first the cold weather got them, then the rabbits ate them, then endless watering with buckets through the drought). So I don't want them eaten by moths next!

Can I spray kill these eggs with an insecticide? I don't want to remove bits of the trees unless I have to, since some of them don't have very many leaves already.

If you are not squeamish just pick them off, if that is all there are. I have found this a fascinating blog. I was a very nasty child who collected moths, butterflies and bees and pinned them on trays after preserving them in methylated spirit. My brother made me trays for them.

I have to agree with Ilex and nearly mentioned it in another follow up post regarding the relative size of the eggs to the Micro Moth suggested but thought that I had better crack on with stripping the wallpaper in the main bedroom. Hate decorating!....hate it!

Do a good job Fractal and it will last for 20 years. On the other hand you might be making work for yourself if it shows up the next room. Howl.

Yeah, thanks for that Sg ;-) Living room done last year. Just the biggie to get round to...the kitchen.....:-o

squish them or cut the tip off as it will be damaged anyway.

If you cut it off now, it will have time to grow some more before the winter. Is the hedge anywhere near the height you want it. If not I would be tempted to squash them and allow the hedge to grow to your desired height. The tops will all need to go eventually and cutting now might encourage this particular tree to bush out sideways rather than keep going up making a bump in the row. If you do not have many eggs, but more than shown, could you hose them off with a high pressure hose without damaging your hedge. Anyone know?

id say you could easily hose them of as it goes scotsgran .

Hi Nosey. Moths and Butterflies produce a secretion when laying their eggs that glues them very firmly to whatever they have been laid on. They won't wash off that easily I suspect :-)

i was thinking more pressure washer or an old clothe and wash the eggs of maybe fractal. ive watched a butterfly lay eggs once .amazing . i hope your well .

I'm no expert but is my info on topping now would send that particular bush out the way, instead of up at the same rate as its neighbours. If so squashing seems to be the only answer. How about dabbing them with a paint brush dipped in meth. How is the paper hanging coming on Fractal.

or get a pin and indevidualy stab them scots lol . im only messing about lol .

Thanks nosey, I am :-)

Paper removal then painting. Gawd, paper hanging?....I'd rather hang myself! Lol

Many thanks for all the ideas.

The eggs are very well glued on - I think attempting to remove them would destroy the shoot. These moths didn't survive for zillions of years by having easily removed eggs!

I have sprayed them with Bayer Provado Ultimate Bug Killer. Does anyone know if this stuff kills eggs?

im glad your enjoying hanging your wallpaper scotsgran lol . i always hated stripping the old stuff of . i dont mind hanging it but i dont suppose that helps much .
i think your going to have to bight the bullit dave and squash them eggs mate .

i'm very pleased to tell you I have never hung paper ever. I have helped taking the old stuff off but my husband is the DIY man around here. I'm sure Fractal will have worked out that you were sympathising with him.

I did:-)