Frist, it is not a cactus but a succulent, Euphorbia. Could be dehydration or too much sun too fast....wait to see what others say.

I say not enough water for this time of year...When you water, you must water thoroughly, so the soil is completely saturated...

I have the same plant, possibly E. ingens or E. ammak, hard to be certain, as some of the columnar Euphorbia are very similar. Mine is less than a meter high, though, and I have not had a similar problem. If you have moved it from indoors to a balcony, it would require more water now than when it was indoors.

Christopher

More Water

Thank you all for your opinions.

It seems to bee dehydration as I also suspect by look of the tops.

But not dehydration caused by little water but caused with underground problems.

I really would like not to cut anything, but maybe that is the only solution (unless some expert told otherwise and give solution).

When I dig dirt I found open wounds, and rotten parts above it :(

{{gwi:582036}}

1. Healty overground part
2. Rotten over-/under-ground part
3. Healty underground part
4. Big worm I found in dirt (english is not my native language so some atributes or names are not correctly choosen; two years before saleswomen told me that worm isn't problem for plants, it cultivates dirt)
5. small, fast, multileg bug found in dirt
-> open wounds

{{gwi:582037}}

So deyidration of branchtops is caused by dameged underground body. It cannot supply enough water and minerals through healty part of body to whole suculent, and most distant parts are suffering.

1. what caused this (bacteria, warm, bug)?
2. how to stop for happening again (new soil, treat with pesticide...)?
3. is there any option not to cut it but heal it?
4. if no, can I save it in one part (cut it, put 5 days on opet air to develop cover on cutted part) or is it to big and I need to cut it in few parts?

This post was edited by ukislav on Thu, Jul 18, 13 at 3:25

Yeah, I would cut it. Cut it until you see absolutely no brown what so ever. Also, you may want to change the soil to a soil with better drainage.

Thank you CactusBoss,

soil is allready for suculents, and we put terracota decorative/drain balls in soil for better drainage.

But soil may be contaminated, so if I do not get other explanation should be replaced with new one for preventive purpose.

Actually, before you cut check to see if the brown part is squishy. If not then it should be fine. If it's squishy than it's rot.

Actually, before you cut check to see if the brown part is squishy. If not then it should be fine. If it's squishy than it's rot.