new growth drop

[incubator01]

So I have a kumquat in good condition, nice green leaves, that recovered from root problems a few months ago. Since the new growth is looking very healthy I was hoping one day the scion would grow a new second main branch. Eventually it did, I noticed a tiny new bud growing at the bottom, well above the graft union (yes, I was very sure) but after a week just gently touching it made it fall off. Thing is, it's not from overwatering as it's planted in the full soil and in greenhouse, nor is it showing signs of overwatering ( no yellow leaves and no other leaves are dropping either).

I'm wondering if a sudden temperature increase from the sun suddenly being revealed after a few days clouds + rain and my greenhouse windows being at minimal opening to avoid excessive rain from entering (and the 80Km/h winds from destroying everything) may have caused this, even though it has a shade cloth against the window it's located near.
I really thought new growth should be more resistant, how are citrus in warm climates otherwise be able to grow? O.o (temperature in greenhouse was with clouds 23°C and without clouds 35°C, I have no option for ventilation, I try to open / close windows as timely as possible and yes I know there are automated windows systems, I just didn't take them)

[Millet]

Temperature of 23 C (73F) will not bother citrus. The temperature of 35C  (95F) will slow/stop tree growth, but will not do damage otherwise. 

[incubator01]

Temperature of 23 C (73F) will not bother citrus. The temperature of 35C  (95F) will slow/stop tree growth, but will not do damage otherwise.

Ok, thanks, that's good to know.
Is there any way to "stimulate" this plant into growing new main branches or will this one single branch become a longer part of the main trunk in the future?
I do have to mention the little bud was perfectly horizontal, as in it made me think of the opposite of a watershoot (which is vertical), so maybe that's why it's dropped?

[Citradia]

I’ve had some new buds sprouting out of a new scion die off too, and it seems that the meiwa kumquat likes to do this more than my other grafted varieties. Another bud growing out again later though. I think kumquats are fussy; I have had more difficulty getting their cuttings, seedlings, grafts to grow than any other variety. Maybe try a horizontal cleft graft. I think I will. I did this with sour orange on PT this year and it’s growing faster than my vertical cleft graft of same variety.

[brian]

My general advice is that if the tree has no obvious problem (rotting roots, dried out leaves, disease, yellow leaves, etc.) and the buds are green it will grow just give it time.  I have had kumquats that seemed to do nothing for many months and then resumed normal growth. 

[incubator01]

I’ve had some new buds sprouting out of a new scion die off too, and it seems that the meiwa kumquat likes to do this more than my other grafted varieties. Another bud growing out again later though. I think kumquats are fussy; I have had more difficulty getting their cuttings, seedlings, grafts to grow than any other variety. Maybe try a horizontal cleft graft. I think I will. I did this with sour orange on PT this year and it’s growing faster than my vertical cleft graft of same variety.

Well this was a purchased plant so I didn't graft it, it definitely was not the cleft graft they used though but other than that the plant is in good health, just like brian said, it's been doing nothing besides that shoot for a while, so I don't expect new growth until next year provided I can get it to survive winter (the rootstock needs much protection)

[poncirsguy]

I’ve had some new buds sprouting out of a new scion die off too, and it seems that the Meiwa kumquat likes to do this more than my other grafted varieties. Another bud growing out again later though. I think kumquats are fussy; I have had more difficulty getting their cuttings, seedlings, grafts to grow than any other variety. Maybe try a horizontal cleft graft. I think I will. I did this with sour orange on PT this year and it’s growing faster than my vertical cleft graft of same variety.

I am so glad to here of your success.  I am very early in my graft of Poncirus Trifoliata scion  grafted to Sour orange root stock.  I was not sure if they were compatible.