On 08/10/2010 10:10, Craven wrote:
Hi, I rescued this one from the point of death about 2 years ago - it
had been sitting in an empty room and hadn't been watered for about 18
months.

It's been doing really well but this year the new growth has gone a bit,
well, brown.

http://www.flickr.com/photos/50869488@N03/5061474587/
http://www.flickr.com/photos/50869488@N03/5061474589/

Can anyone provide any assistance please?

First off they are not cacti, they are Euphorbias with irritant milky
caustic sap so be careful if you take cuttings. People who grow the most
dangerous ones also grow Aeonium Lindleyii which is alleged to be a
useful antidote to euphorbia sap. Some of the desert species are a lot
more chemical warfare inclined than their temperate cousins.

I think this website over eggs the threat somewhat, but the message is
that you really do not want to get the sap in your eyes or on any other
sensitive parts of your anatomy (including skin).

OTOH it does make them largely immune to most pests and diseases.

I suspect it is corking due to sudden exposure to strong sunlight
scorching the growing tip - a natural response to damage. It should not
harm the plant though may be unsightly.

Regards,
Martin Brown