Help w declining yellow orchid vine

[rudedog830]

I have a few yellow orchid vines that were planted about 3 months ago and are in decline. There are three factors that I think could contribute:
1) I live in PHX and we have experienced record heat in the last two weeks. They are in full sun. Despite that, the plants have never gone dry and are watered by drip system.
2) I've seen a white powdery substance mainly on the stems, both mature and new.
3) Many leaves show the spots as in the image.

I have sprayed with a potassium bicarbonate solution a couple of times (at night only). I've also sprayed once with neem oil.

I would appreciate if someone can help me diagnose the likely cause of the decline and a recommended treatment.

 

[jm0928912]

I bought orchids several times, but they soon disappeared. also interested in tips

 

[Marck]

Hello and welcome to the Forums.

The Yellow Orchid Vine (Callaeum macropterum, formerly Mascagnia macroptera) is not an orchid at all, but rather a woody vine in the Acerola family (Malpighiaceae). It is native to Mexico and southern Arizona. Another useful common name is Yellow Butterfly Vine.

Establishing these vines in summer in Arizona may require some additional water beyond the drip system. It is not clear to me that there is a significant pest or disease problem, but if you believe so, please do send an update with more photographs.