Is Laburnum poisonous?

About a year ago Joe contacted me wondering whether a Laburnum tree was going to pose any problems for the animals in his pond.

He wrote:

“I have a wildlife pond under a Laburnum tree… are the fallen leaves dangerous for the frogs or tadpoles? I know they are poisonous for fish, but can’t find out if there’s any risk to other animals.’ I’ve tried searching everywhere for help on this, but I thought you guys might know! Is the poison soluble do you think?”

And here is said pond.

Underneath the spreading Laburnum tree.....

Well….Laburnum was, at the time, just another of the many subjects about which I didn’t really know anything, but elsewhere on the web you can find somewhat apocalyptic warnings like:

“All parts of the Laburnum tree are poisonous: the leaves, bark, wood and especially the seeds. They contain the alkaloid cytisene. Just half a dozen of the little round black seeds can kill a small child. There is a variety that has seedless pods call Laburnum vossii but that still does not solve the problem of the poisonous leaves, and even the pollen from the flowers is poisonous. Any of this material allowed to fall into a pond or pool can only have a detrimental effect on the life in the water.”

Sounded pretty dire – as though having said tree would be a bad idea – perhaps only marginally better than setting up a shelter for mad axe murderers in the garden shed.

So I had a little dig around.

It turned out there wasn’t much in the way of facts on this subject – nothing new there then – and some hints that the ‘a-handful-of-seeds-will-kill-a-small-child‘line was a bit of an exaggeration. I’ve copied what I wrote to Joe at the bottom (it goes on a bit – people politely call these answers ‘comprehensive’) but the gist of it was – well, it doesn’t look too bad, why not just see if frogs survive in your pond?

So it was very interesting to get a report back from Joe today that:

“So far the Laburnum is not having any noticeable effect on the wildlife. The pond has dealt with fallen Laburnum leaves last autumn, flowers in the spring and now pods are dropping into the water too. Despite this there are masses of tadpoles (mostly now mini-frogs), four resident adult frogs, and I spotted my first smooth newt yesterday (very excited about that as I haven’t seen newts in the area before!).

So far good! I also noted masses of bees on the Laburnum flowers so it must have some nectar value too…[remember…’even the pollen from the flowers is poisonous’].

So, maybe Laburnum isn’t so bad after all – though probably you would need a PhD to know for sure.

Still, as it’s related to nicotine (and apparently used as a substitute if you’re trying to kick the habit) it’s probably not a good idea to sprinkle the seeds on your toddlers organic muesli to give them a boost in the morning.

THE ORIGINAL REPLY TO JOE

From: Jeremy Biggs <jbiggs@pondconservation.org.uk>
To: joe.berry@yahoo.co.uk
Sent: Mon, 9 November, 2009 8:10:52
Subject: From Pond Conservation

Hi Joe

There is no information out there to answer this question exactly because, as far as I can tell from the scientific literature, there have been no  studies of the effects of this chemical on aquatic organisms.

One thought is, if you get frogs, spawn and tadpoles and they grow up successfully, it’s probably not doing much harm.

The toxic chemical in Laburnum is cytisine which is one of a group of chemicals known as quinolizidine alkaloids. I’m not a biochemist but scanning the scientific papers on the subject this is related to nicotine, and apparently it’s used in medicine as a nicotine substitute for people trying to kick the habit.

Cytisine (there are similar chemicals in lupins and other legumes) is a pretty active chemical and people are experimenting with it as an insecticide for terrestrial insects. If it’s anything like nicotine, which is a pretty good all round killer, it could be quite toxic. There is also some evidence that it can be passed from one trophic level to another, from caterpillars eating the plants to parasitic wasps.

However, and there are quite a few ‘howevers’ coming here, I wouldn’t rush to get the axe out straight away!

How toxic cytisine is in water, there is no information about. There is a bacterium that breaks it down, so it’s quite possible even if it does get into the water it’s quickly broken down. And the gist of some of the older human literature is that its toxicity to vertebrates is exaggerated.

Plant chemicals like cytisine are generally interpreted as a form of chemical defence and, as far as I understand it, they work by making the insect (or whatever is doing the eating) use up energy to de-toxify them. So they don’t necessarily kill things.

As there is no clear answer to this question at present (the suggestions on the Wild About Britain website that it would need a PhD is on the right track!) you might want to make a few observations yourself to assess the scale of problem.

For example you might compare your pond with neighbouring ones: if frogs spawn in your and neighbouring ponds but never succeed in yours this might be a hint of things going wrong. But it could of course be one of many other problems.

You could look at the animals as well: if you have a normal amount of creatures in the pond (work out the Big Pond Score for your pond) then its probably not doing too much harm.

Best wishes

Jeremy

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2 Responses to “Is Laburnum poisonous?”

  1. CHARLES BRITTON Says:

    Hi Jeremy,I wonder if you can give me some guidence regarding the poisonous effects of the dreaded laburnum.In my garden,the seeds have been falling off the tree and landing in the birdbath.I have never considered before the possibility that this could effect our avian friends.But,one morning,we found the bodies of a couple of bluetits who had a nearby nest.They had been drinking out of the birdbath…So,could the water have been poisoned by the seeds?One was actually found in the birdbath itself!Your advice would be very welcome.

  2. Kerin Says:

    I wouldn’t assume that the mode of action in insects, invertebrates, birds and mammals will all be the same for alkaloids.

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