So, this literally happened over the course of 2 days. On Sunday morning the plants were fine. However, the humidifier in this room malfunctioned on Sunday while I was not home for about 4-5 hours and I came home to find an empty humidifier and the plants were at 99% humidity. I immediately put up a couple of fans so that they could dry out faster. Another thing to mention is that this week, the temperatures here have been skyrocketing and at times the plants are at 35C (95F).

Since Tuesday I noticed that yellow spots have appeared on the leaves of ALL of the gloriosums. It is only on the gloriosums in this room (there are other philodendrons, anthuriums, etc in there as well) and no, they are not clustered together. There is a physical distance of at least 1m between some of the Gloriosums while others are closer to lets say an Anthurium than another Gloriosum. The yellow spots are on ALL of the leaves, except for the newly growing and unfurling leaves.

The plants are in a very well draining potting mix, humidity ranges between 55 to 70%. The temperatures were usually between 28-30C (82-86F) except for this week, as now it is just hot. I inspected them throughoutly and I just do not see any pests problems. Based on google search, some other person had thrips with the same signs but I just do not see them and I have had last year a thrips problem in another room, so I know what thrips look like and the damage that they cause on a monstera, unsure how they affect the leaves of a gloriosum.

Photos of the yellow spots and the backside of the leaves:







Does anyone have any idea what might be going on? Maybe @Gina1960? I am completely baffled, so any thoughts are much much appreciated. Thank you in advance!

I can only speculate that the plants have been stressed, perhaps by heat. My gloriosums are almost always in temps of 90+ at this time of the year, and the humidity here is extreme, 80-100% at the moment. If yours are not acclimated to those conditions and suddenly they are living in them, it may cause some problems

Gina1960 said:I can only speculate that the plants have been stressed, perhaps by heat. My gloriosums are almost always in temps of 90+ at this time of the year, and the humidity here is extreme, 80-100% at the moment. If yours are not acclimated to those conditions and suddenly they are living in them, it may cause some problems

Thank you Gina! I also think it's some sort of physiological stress as it literally happened in the course of two days and has not progressed any further.

May I ask another question just to exclude it: in your experience, does it look like damage from thrips? I am asking as I've noticed that thrips damage presents itself different on different plants, eg: when I had them, the damage on monstera, white wizard and pothos, appeared completely different visually. And I have no idea how does thrips damage look on a gloriosum. Since I had to deal with thrips last year, I've grown to be suspicious and they are the first thing on my mind.

No, it doesn;t look like thrip damage to me...and if it was, you would probably still be seeing them. When I have found thrips, it looks like they have actually caused a scrape on the plant as they chewed on it. That looks internal to me. To be safe, I would probably treat the leaves with a fungicide.

Gina1960 said:No, it doesn;t look like thrip damage to me...and if it was, you would probably still be seeing them. When I have found thrips, it looks like they have actually caused a scrape on the plant as they chewed on it. That looks internal to me. To be safe, I would probably treat the leaves with a fungicide.

Thank you once again, Gina! Another question (sorry if I'm bugging you in advance but since I couldn't figure it out...) do you know what they spray plants with to prevent a pests problem? Sometimes, plants that I order arrive with signs that some powder (redish-brown) was sprayed on them, so was wondering what are the nurseries using to keep off pests? Or maybe what are you personally using since you have more valuable and detailed knowledge than pretty much anyone I know haha

I think that is extremely variable. When you say you 'order', do you mean 'import'? Like from Thailand or Indonesia? Or do you order from a nursery there in Germany?

The process for decontaminating imports is completely different from the process of making sure a plant has no pests to send it through domestic mail, and, I am sure that in every country, every seller uses something different

Gina1960 said:I think that is extremely variable. When you say you 'order', do you mean 'import'? Like from Thailand or Indonesia? Or do you order from a nursery there in Germany?

The process for decontaminating imports is completely different from the process of making sure a plant has no pests to send it through domestic mail, and, I am sure that in every country, every seller uses something different

No, not imports. Sorry that I didn't make that clear. From nurseries in the EU. Sometimes they arrive with what seems to be the same red-brownish powder on some leaves and I'm wondering what is that. Or what to use preventively against pests.

I have no idea, we don;t have that happen here. The only red/brown I can think of would possibly be Copper fungicide residue

Gina1960 said:I have no idea, we don;t have that happen here. The only red/brown I can think of would possibly be Copper fungicide residue

Oh, I see, thank you. And is there anything that you personally use as a preventive measure against pests? I'm asking as I'm still scared to my bones of thrips lol.

My P. gloriosum also gets yellow spots on older leaves. And other Philos too, but not all. Best answer I dug up: it's nectaries. There is not much info on them. Some species produce them to attract ants or other insects. On mine I noticed that they are absent when plants are cooler and drier. But appear again when they get watered more . But my spots are not translucent areas like yours.
How much water to they get usually? When temps are over 90F with high humidity plants transpire less and soil mix stays wetter longer : perhaps this is oedema from absorbing too much water?

skylark said:My P. gloriosum also gets yellow spots on older leaves. And other Philos too, but not all. Best answer I dug up: it's nectaries. There is not much info on them. Some species produce them to attract ants or other insects. On mine I noticed that they are absent when plants are cooler and drier. But appear again when they get watered more . But my spots are not translucent areas like yours.
How much water to they get usually? When temps are over 90F with high humidity plants transpire less and soil mix stays wetter longer : perhaps this is oedema from absorbing too much water?

Thanks for your input and reply!
They are usually on a 1 per week watering schedule (every Sunday). I skipped watering them for 2 days after the humidifier issue as all the plants were just soaking wet and it looked as if rain had poured in the room lol. But since they are all in transparent pots so that I can see their moisture level, by Tuesday they looked bone dry so I watered them once again. And on Thursday I spotted the issues with the Gloriosum. I am also suspecting a physiological issue like Edema on the gloriosums as i saw some translucent tissue on the melanos as well but boy, did the gloriosums overreact!

I know what you mean with the nectaries, I noticed that the gloriosums and my caramel marble (not in the same room) are producing them quite frequently but so far could not pin point whether it's beneficial to them or not. And I have been rather worried that it might be attracting bad pests?

Outside 'the sticky dew' might definitely attract something undesirable. But indoors you should be fine. I keep mine in jungle mix : bark/coco-chips/large perlite with some part and coir peat . Super fast draining but still wicking: they are all on rope wicks for self-watering. They don't usually take much water indoors as it's about 75f. But with wicks it's self regulating so to speak: they absorb what they want only. I keep my pots small to get them dry faster too. I'll show you the relative pot to plant size on mine for reference.
When I get a lot of dew I just spray them with light soap solution ( a few drops per 2qt) and let them dry in the shower overnight. The sewing then stops somewhat. I have not found anything to stop it. I find it unsightly.

Extrafloral nectaries have a certain 'Look' to them. They only occur in Araceae in Philodendron and Alocasia. This does NOT look like extrafloral nectaries to me.

I use Orthene both prophylactically and for things I see on my plants. But its not for use in a house for houseplants. I have a very large greenhouse, and a nursery license, and I am able to use it without a pesticide permit. But its a very old school organophosphate pesticide, quite toxic, that was taken off the market for home owner use except for a Fire Ant preparation they make.

I agree, the nectar spots are well defined , but OP yellowing areas are sort of faint roundish, larger then nectar spots. That's why I think it's related more to excessive water retention.
my Alo 'Poly' are super sensitive to amount of water I keep them very tight in small pots for that reason especially when young and small.
So here's my newish rooted cutting of P. gloriosum : new 3 leaves popped in last 6 mo, so growing fast. It's in 1qt transparent pickle deli container 😏. Barrel pickles are glorious too 🤣. So far no spots. It's in Fl so high humidity about 65-75 % and 75-77 F temps.

Gina1960 said:I use Orthene both prophylactically and for things I see on my plants. But its not for use in a house for houseplants. I have a very large greenhouse, and a nursery license, and I am able to use it without a pesticide permit. But its a very old school organophosphate pesticide, quite toxic, that was taken off the market for home owner use except for a Fire Ant preparation they make.

Is this acephate? If so, I managed to get my hands on some just in case together with acetamiprid and spinosad (which is no longer for sale freely in the EU and is quite hard and costly to find). I do not plan to use the acephate on the plants that I live with but over the coarse of some months, I have created a special room dedicated to some rare species and want to keep them as safe as possible. May I ask how often and at what strength do you use it preventively? And how long does it keep them safe? And at what strength if you notice a pests problem?

skylark said:I agree, the nectar spots are well defined , but OP yellowing areas are sort of faint roundish, larger then nectar spots. That's why I think it's related more to excessive water retention.
my Alo 'Poly' are super sensitive to amount of water I keep them very tight in small pots for that reason especially when young and small.
So here's my newish rooted cutting of P. gloriosum : new 3 leaves popped in last 6 mo, so growing fast. It's in 1qt transparent pickle deli container 😏. Barrel pickles are glorious too 🤣. So far no spots. It's in Fl so high humidity about 65-75 % and 75-77 F temps.

Oh, they look gorgeous! Mine were just the same before that stupid humidifier acted on its own will. Thankfully, the spots have not been spreading. I have treated with a fungicide and will be keeping my fingers crossed that they just reacted to a humidity stress. The rest I'm their room are doing well and growing so far.

What's the wicks method for watering them that you mentioned? I might have switch to that if it is an efficient way to watering them as currently my collection takes a good day go be watered haha.

you have lechuza pots in germany : they are self-watering. they use a bottom layer of fired clay that roots grow thru (the top layer is soiless mix). you can also grow in pure lechuza pon (that's clay pellets). there was a guy i followed with astounding pics of Aroids in lechuza pots.
you can read up about them, the principals that they used.
here's his flickr aroids album:
https://www.flickr.com/photos/...
so i adopted this idea: i mix my own light jungle mix and wrap the inside of the pot with coir matting to allow for extra air (very easy to pop-out to check how the roots are doing, no mess at all) and i add a braided rope with acrylic core on the outside of coir circling the bottom of the pot and rising up to the top. the rope wicks the water solution to the mix. it's passive hydro set-up but roots are anchored in the soiless mix.

this article is in polish( you can google translate or not) just look at pics: there's a philo with spots: nectaries...pretty awful! a guess, that's what they look like at their best
https://gangroslinny.blogspot....
gina, do you have any pics of nectaries on leaves? i find mostly the ones on stem/petioles.
there was a pic i took in Fairchild where some leaves were good some others covered in spots. does that look like nectaries? or bacterial ? it's on P. subincisum


i only took top of leaves , unfortunately. may be i'll find more later..

Yes Orthene is acephate