Not sure, I can't acess your other pics.

Do you have borer insect as over here they creat havoc with Robinias.
Heather

It looks very like the damage I have seen inflicted on some other leguminous trees and shrubs by a thin blackish caterpillar withh yellow spots, that can explode in plague proportions in summer. It seems to have a narrow food preference, eating only a few legume genera: ones I have seen eaten are Sophora, Laburnum and Genista, but Robinia seems a possibility. Look for 'cobwebs' on the foliage, with black droppings caught in them; caterpillars are well camouflaged.

Of course I could be quite wrong, your photos hardly show enough detail to be sure.

Hi Heather and Tony,

I am sorry I hadn't seen your replies over all of this time!

When I get home from work I will update the pictures to something hopefully more beneficial.

I have not seen any insects through the foliage and now another tree is going through the same thing. I have three trees in a row about 3m apart, and whatever is affecting them has started on the right tree, now the left tree (4 weeks later) and the middle one is still leafy and green.

The trunk and thicker parts of the graft are green when I lightly scratch the bark, but the twigs and leaves are dead. I have trimmed the first one back and am about to trim the second one back. At the moment it is just a dead looking tree. I have given them a seaweed fertilizer too.

I will have a closer look for any evidence of insects and report back.

Thank you!

Lauren

approx 4 years ago we had an infestation of spikey caterpillars on the genista and i found out from a branch of the university in abbotsford that it was the painted apple moth. after spraying it came back the next year but after treatment it hasnt returned.a beautiful moth but horrible caterpillrs.i was always scared it would get on other plants but it didn't.
regards chas

I checked the trees yesterday. Nothing. No caterpillars, no webs and no coocoons. On the middle leafy one I noticed some ants and a couple of mealy bugs. I've sprayed with white oil.

I've emailed an online nursery in Melb for advice since they grow them and seem to promote having being the founders of 'inventing' them, but have heard nothing back (don't blame them since I bought them in NSW and not from them).

I rang the local hardware store chain where I bought them to see if they had any replacements - $109 ea!!! I paid just over that for all 3 of them less than a year ago!

Thanks for your help

Cheers,
Lauren

Well I think I've found the problem. There are a couple of what appears to be borer holes :(

I found another link that is referring to the borers in NZ, I'll continue trying to revive them, but I hold low hope.
http://www.rnzih.org.nz/Plant_Doctor/WG143_Mop_Top_Robinias_causing_headache.htm

Thanks for your help everyone.

Kind regards,
Lauren

Here is a link that might be useful: Borer Hole in trunk