Looks like mealies! Use a magnifying glass and you should be able to see for sure!

Thankyou for replying!! How small are we talking? I can't see anything crawling about. I've look with a magnifying glass (although not a particularly strong one) but can't really see much apart from the clear sticky stuff. It definitely seems to be spreading though! If I treat it for mealybugs even if it's not that, will it harm the plant? Thanks again!

The mealies are the white things lined up in a row on top of the leaves. They look like a tiny piece of cotton.

My calathea plant has the exact same situation! You described it really well. Mine also has new growth and no dropping leaves. I have been searching the internet to no avail. It doesn't look like mealy bugs to me. I've dealt with mealy bugs on other plants before and this is markedly different. I tried using a washcloth with warm water to wipe the sticky substance off and that helped for about a week...then on some leaves (not all) it came back. I also noticed a spider hanging out in the plant...could this be something related to a certain kind of house spider? Kimiko84 have you noticed a spider on your plant? Any other ideas from folks much appreciated!

Hello! I'm afraid I never quite worked out what the problem was.. I also don't think it was mealies in the end.. I chopped off the worst leaves, and quite heavily sprayed it with an organic bug spray.. twice.. it didn't really seem to do all that much, but it also didn't seem to get much worse, and by the summer, it had calmed down. Then this spring, a similar thing happened, but as it didn't die the first time, I didn't panic, and just chopped off the most unsightly leaves.. and repotted it (I didn't repot it the year before when it first happened as I was worried it would be extra unecessary shock, but it was getting quite root bound so I risked it this time). It has been fine ever since.. had loads of new growth. It made me wonder if it was a seasonal thing, as both times it was in the spring (possibly to do with the central heating going off?! I don't know!!) Anyway, if it is the same thing that happened to mine, I wouldn't worry too much, as like I said.. it never escalated into anything worse. My Calathea is going pretty strong now.. over 2 years after I bought it.. I get dry leaf tips a bit because I just don't think it's humid enough in the house, but other than that.. it's pretty healthy! I will keep an extra close eye on it in the spring again though, just incase! I hope you solve it, and if you do, I would love to find out more, but fingers crossed it will be fine anyway! They're such beautiful plants!

I've got the same problem with my "calathea". Thank's Kimiko for the info i'll stop worrying and repot it. My guess would be that it lacks some specific nutriënt making it excrete sugar.

By the way: while looking for cures on the internet i learned that our "calathea" is not a calathea. It's a ctenanthe!

It requires more or less the same care, but there's one difference: it's much easier to propagate, you can even take simple cuttings! I will definitely try this.

Ah brilliant! Thanks so much for that! I'm always a bit sceptical as to whether plants are labelled correctly - especially given I bought mine in Lidl so it just had a bit of a generic label.. in fact I think it may have even said Maranta/Calathea?! So that's great info to know! I will definitely try cuttings too! Thank you! And yeah.. a nutrient deficiency would make sense.. I've never fed mine.. I didn't want to risk stressing it further so just stuck to rain water, and as it's now 2 years on and doing pretty well, I thought I'd stick with that! Mind you, if I make successful cuttings, I could try some experiments! Thanks a lot!

Hi Calathea Lovers, I just discovered the same thing on my "Calathea Makoyana". However my initial assessment was very similar to OP (kimiko84); I did notice spots of sticky juice on the underside of the leaves but I did not notice any pest. When I went on to google what it was, one pest that seems to leave a sticky residue was the scale bug. But as with OP, I didn't see any such pests on my plant. So strange!! Watch out for bugs though, I would imagine the sticky sap would be inviting for ants or some other bugs.

Hi Ctenanthe owners, I have this plant which has what appears to be the same problem Kimiko84 has, but on close inspection I discovered small mites on the underside of the leaves. Today I sprayed under all the leaves with Enviro pest oil and after 2 hours used a fine water spray which removed most of the oil and also disolved all the sticky deposits. The leaves look great at the moment, and hopefully the situation has been rectified. But somehow I don't think the sticky deposits were created by the mites - time will tell ????????

I noticed my calathea was sticky too. Looked on underside and didn’t see scale (brown) or mealy bugs (cottony white). Thought maybe it was just sweating. I looked again today and there are tiny white things on the underside of the leaves and they were crawling! Still can’t identify what they are. Trying detergent and water spray. Two new leaves are getting ready to unfurl. Hoping itt survives!

Hi to all above commenters, I too have stumbled across this post after finding the same thing on my calathea. I sprayed my little friend with neem oil and used a paper towel and more neem oil to scrub off the white buggies under the leaves. I believe these are spider mites. I'm planning to give my calathea a little time and then maybe a shower soak. I'm hoping for some rain instead of tap water. Wish me luck!

I find this post so interesting. I to have a Calathea. It is called pinstripe or not at Lowe’s where I bought it. It is a wonderful plant and seems to be growing well except that it has these sugar like granules in the top of the leaf occasionally and this morning I found a sticky substance with the same sugar like granules on the lower side. It sounds like we may be talking about the same thing. I will spray with Netra name oil which is said to control for aphids white flies and spider mites I’m on other pests. Cell phone suddenly not working. Apologize for misspellings.. Looking forward to any comments.

Thank you YC Ong. I have a similar issue with my Ctenanthe oppenheimiana. Tiny beads of clear sticky sap like substance on the underside of the leaves. other plants in my home have been attacked by wooly aphids and scale and so I treated my Ctenanthe with home made white oil. Then I read the article on the link posted by YC Ong and it seems that it may just be a response to being a bit dry.

Yep, it's definitely dryness response... I had forgotten to water mine, and that's what happened. Causes can be being rootbound, drop in humidity, and change in environmental conditions. Its certainly not scale, mealies or spider mite. As always, look at it with a jewellers loupe, or magnifying glass... As a keen gardener, I always carry a loupe when doing my indoor/outdoor rounds. This particular phenomenon is a sugary excretion - if not noticed quickly, it dries into a sticky crystalline spot, and leaves a transparent spot on the leaf underside. I have cleaned it off with soapy water, and a fresh water wipe afterwards

Any little bugs will have been attracted to these sweet secretions, they are not the cause.

Logged into Houzz for the first time in years just to say thank you YC Ong - this was 100% water stress, not mites of any kind. So if you can’t see signs of bugs but have the sticky crystals, try upping the watering (and in my case repotting to separate out some plants from the clump and give the remainder some more space / fresh potting mix). Worked almost instantly!