I've successfully rooted 6 dipladenias 4 month ago, they are in pots since 3 month. All went well so far, but now it seems they have some illness or pests. (All the six, although in different progress)

I am an absolute beginner, so I just hopelessly see their day by day worsening condition, and I am a bit worried my original two older ones may also get infected.

Could anyone identify what the problem(s) is/are, and most importantly what to do to cure? Is it virus, or pests? (I do not see bugs neither on the back side on the leaf, and when I try to touch or get something with my nails, nothing detected (but again this is the beginner speaking)

Detailed plant and environment info:

Location is Budapest, Hungary, it's autumn first month September now, temperature is approx 25 C / 77F, now, the pots are in very well lit outdoor place. It seemed to me that dipladenia (both the older 2 and also the 6 rooted very flexible for water supply, never dropped a leave since spring, they got relatively less water.

Please note...

I prefer use only absolutely harmless chemicals and methods, as I have no appropriate protective gear.

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up vote 3 down vote accepted

Since we are in full summer in the northern hemisphere this is probably just natural ageing of the leaves. I have Mandevilla/Dipladenia plants as well, and a few leaves are turning yellow and showing spots as yours do. So it is probably nothing more than the leaves having finished their work. Give the plant full sun, as much as possible, and while keeping watered make sure the roots have free drainage.

The test, as with other discolouration of the leaves, is if the leaf falls off naturally. If it dries up and remains stuck to the plant then that is a problem; the natural separation of the leaf from the plant has not had time to happen and you need to look further. If however it falls naturally (or when you gently tug on it it lets go easily) then the leaf has completed its work and would, in a natural environment, decompose and return its chemical components to the underlying soil.

  • Many thanks, sounds as a relief. The two big plants (2 years old, 1 meter high) were yellow leafs, but I never noticed red spots. Anyway I hop the best – g.pickardou Sep 15 at 19:20
  • Yes, the leaves fall, so it seems to be OK – g.pickardou Sep 23 at 19:20

Your overnight temperatures may be causing a problem - these plants don't really like temperatures below 18-21 deg C at night, and I think your temperatures have dropped below that recently. That, coupled with shortening daylight hours, likely means its time to move your plants to somewhere like a greenhouse or a conservatory to overwinter, for they are not hardy where you live. They won't die immediately, but as soon as a frost arrives, they won't last long after that if left outside. https://www.gardeningknowhow.com/ornamental/vines/mandevilla/growing-a-dipladenia.htm

  • Yes I know I have to care about them in the winter, but I did not think about this soon. Last year they did in the room in a very well lit place, but, half of the leaves (or less) fallen, but the plant developed very thin and long parts as it oriented to the light, so springtime I practically cut back all, and during 4 weeks it practically reborn, with all new and strong parts. As a consequence I try to rest them this winter in 10-13 C, and allow they leaves fall, and cut back them next spring. The six new small may or may not manage to survive, so maybe they will got different care... – g.pickardou Sep 15 at 19:27
  • I'm in the UK - its rather cool for September, despite having an extremely hot summer. Your forecast temperature tonight is just 14 degC, followed by more nights at 13deg C or below - perhaps you're having a cooler September than usual as well, maybe? – Bamboo Sep 15 at 22:03

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