Dipladenia with new brown leaflets

Question: Dipladenia with new brown leaflets

Goodmorning everyone,
I would like to ask for advice for my Dipladenia.
It was great until ten days ago. All dark green and shiny leaves, a couple of buds. Then, I don't know if with the arrival of heat (I live in Barcelona), some leaves have started to turn yellow. If I look under the leaves, the lower surface has green spots, like bubbles.
But the thing that worries me most is that now I have noticed that the new leaflets are brown and curled ...
There are too many things that could be the cause, and I would like to go by way of exclusion until I consider the (or the) most likely to act accordingly
1) Could it be the heat (it's only exposed to the morning sun, until noon)?
2) the red spider mite (I have some on other plants, but I have not yet seen on the Dipladenia)
3) have it fertilized? A month ago, I spread some granulated fertilizer tablets (about fifteen, on a 18 cm diameter jar)
Thanks in advance!

Answer: Dipladenia with new brown leaflets

Dear Anna,
we say that all the causes that may have contributed to the conditions of your dipladenia:
- the dipladenie love semi-shady positions; they tolerate direct sun, but possibly only for a few hours a day; unless they belong to the sundavilla variety, which worships the direct sun, even all day.
- perhaps the fertilizer is too much, but if you have used a granular fertilizer you should be able to remove about half of the granules (although in fact, it does not seem to me that it is an excessive quantity).
- with good probability your dipladenia was attacked by some parasites, such as cochineal, red spider mite or aphids; the bubbles under the leaves suggest the cochineal, which, together with the red spider, refers to a warm, dry and poorly ventilated climate. To eradicate these insects you can try a systemic insecticide-acaricide, that is to say that it must be supplied in the water of the waterings, and enter the plant in a circle. In this way it should not create problems for the useful insects that rest on the flowers, but should defeat all the insects that feed on the leaves. Look for a systemic insecticide and acaricide in the nursery, asking the nurseryman to advise you if necessary; these are specific products, which must be used in the soil and not sprayed on the leaves; they also exist in tablets, to put in the jar, which melt every time you water. Always check that the insecticide you are using works against the insects or small spiders you want to get rid of; and therefore on the label the insecticide must specify to work against the cochineal, and also to be an acaricide (the red spider mites are not insects, and most of the insecticides leave them perfectly free).
In any case, since these are insects that develop in very hot, dry and poorly ventilated conditions, try also to move (if possible) your dipladenia to a slightly more shaded and possibly even more ventilated area; and when you remember, in addition to watering it, it vaporizes the leaves with distilled water.