Picked up gnat infested Dendrobium in bloom

[IvyElle]

Hi, everyone! I'd just recently gotten into orchids and bought my second one, a white dendrobium, about a week ago. I held off on repotting because of my past experience with my phalaenopsis- I moved it from the store sphagnum moss into bark while it was in bloom and was greeted with some lovely limp leaves and it completely dropped flowers. Lesson learned. So to prevent that from happening again, I left this dendrobium in the moss.
However, I've just discovered what appears to be gnat larvae in the moss. I'm not sure if I should repot while it's still in bloom because I don't want limp leaves or to lose the flowers or if I should use a pesticide. I was planning on moving the orchid into bark eventually anyway, but this is much faster than what I planned for.
Thank y'all for reading any help and care advice is appreciated.

[SouthPark]

There is a product called 'mosquito dunks' that can help keep the gnat situation under control.

[Roberta]

First, Welcome!
Gnats don't harm the orchid. You probably don't want them in your house, the mosquito dunks mentioned by SouthPark will go after the larve, also BT (Bacillus thuringiensis), the active "ingredient" in the mosquito dunks will do the same. It is harmless to people and pets (unlike many pesticides) They ARE an indicator of the medium being broken down, so repotting is in order.

A question about your experience with the Phalaenopsis... In general, Phals can be potted while in bloom and don't miss a beat. If they are in a bad/soggy medium, it's generally a good idea to repot since they can stay in bloom for months and in the meantime roots die. So... when you did it, what did the roots look like? If they were bad, it wasn't the repotting that did it. However, it sounds like maybe it just got too dry - bark dries out a lot faster than sphagnum, so after repotting, it the plant needs watering a lot more often than it did in the soggy sphagnum. But the roots will be much happier. A Phal in fresh bark can need watering every 2 or 3 days - and thrive that way because the roots are getting lots of air. (If you watered it at "sphagnum" frequency, it just got dehydrated)

Dendrobiums are ideally potted when new growth is appearing (which will happen in the next few months) But if the sphagnum is soggy and broken down (gnat larvae being a good indication) repotting now is likely a good thing to do. Just remember, you'll need to increase the watering frequency, but with an open, well-drained medium like bark, over-watering is not likely a problem.

[camille1585]

Originally Posted by Roberta

First, Welcome!
Gnats don't harm the orchid. You probably don't want them in your house, the mosquito dunks mentioned by SouthPark will go after the larve, also BT (Bacillus thuringiensis), the active "ingredient" in the mosquito dunks will do the same. It is harmless to people and pets (unlike many pesticides) They ARE an indicator of the medium being broken down, so repotting is in order.

Actually, fungus gnats larvae can harm plants. While they prefer to feed on fungi in the substrate, they often feed on roots as well. If it's a mild infestation then it doesn't really affect the plant too much, but in more severe infestations they can do significant damage. That being said, it doesn't change the fact that they are a sign that the medium is old and needs replacing.

[Orchidtinkerer]

more importantly, it could also be something that isn't gnats...
I generally wouldn't advise repottnig in bloom but I have done so lots and it should certainly not cause limp leaves!!

If it does then more than just a repot at a bad time occured.

Repotting when buying a new plant is essential. Will every plant from the shop do badly without a repot? Certainly not.

Just like in russian roulette there is a 5 in 6 chance everything will be fine. But why take that risk and gamble is what I say?

If you are ok with a 20% odds that the orchid could suddenly go downhill (and if it does it is too late) or would you rather check what you have received (not just the iceberg on top but what is underneath too).

I understand you had a bad experience repotting your first orchid and it would help to know what happened, repotting from moss to bark, even if the plant were to dry out as a result it would take weeks for the plant to suffer as a result. Bacterial infections due to soggy moss however will progress fast even if you repot it into bark at the first sign of a problem (ie once its too late)

[IvyElle]

Thanks for the advice, everyone! I’ll definitely be repotting the Den.

Originally Posted by Roberta

A question about your experience with the Phalaenopsis... In general, Phals can be potted while in bloom and don't miss a beat. If they are in a bad/soggy medium, it's generally a good idea to repot since they can stay in bloom for months and in the meantime roots die. So... when you did it, what did the roots look like? If they were bad, it wasn't the repotting that did it. However, it sounds like maybe it just got too dry - bark dries out a lot faster than sphagnum, so after repotting, it the plant needs watering a lot more often than it did in the soggy sphagnum. But the roots will be much happier. A Phal in fresh bark can need watering every 2 or 3 days - and thrive that way because the roots are getting lots of air. (If you watered it at "sphagnum" frequency, it just got dehydrated)

Dendrobiums are ideally potted when new growth is appearing (which will happen in the next few months) But if the sphagnum is soggy and broken down (gnat larvae being a good indication) repotting now is likely a good thing to do. Just remember, you'll need to increase the watering frequency, but with an open, well-drained medium like bark, over-watering is not likely a problem.

About the phal- when repotting it, the root system looked pretty healthy, no mushy rotten roots. I cut off the few dry, brown, wilted ones. I agree with you, my error was definitely my failure to increase watering frequency. I was watering about once a week in the sphagnum moss. Looking back on it, it feels so ignorant of me to not change the frequency, haha. Thank you!