Dendrobium ailments

[TwoStems]

I've had this NOID den for about a year and a half, it seemed to be doing well once I repotted it in s/h about this time last year. Since repotting it's growing a lot of new canes (about 4 so far), but while checking it today I noticed some of the old canes are now yellow and squishy (feel hollow). There's a faint smell of sulfur if I really put my nose in the plant. I'm wondering if maybe I just water this guy too much? I try to make sure it dries out before watering again, but I can't always tell if the leca is completely dry before I water. Do I maybe have it in too big a pot? I'm taking it home tonight to investigate further.




I also noticed awhile back that I've got some yellow/brown spots on some of the leaves of the oldest new cane. I assumed it was getting too much light and moved it out from directly under my grow light, but I want to make sure it's not something more serious. Any help is appreciated! Thanks!!

[Dorsetman]

The yellow squishy cane is the oldest one ; they do die off naturally, and if grown in a dryer compost they just turn to something like straw . In the wetter compost they rot. No problem, just cut off at ground level, unless you are repotting, in which case cut through the rhizome to take the old cane away together with all its roots. You can be sure that the roots from that cane are dead too. I'm not sure which happens first, but whenever a growth is dead the roots are too - chicken and egg...
The leaf damage looks to be insect originated , but it is difficult to diagnose from a photo. Each brown spot is actually bacterial damage , the bacteria/spoilage organism entering the cells at the site of an insect puncture. Can't do anything about that once its done, except look out for critters - which can be microscopic !

[TwoStems]

Thank you Geoff! I haven't noticed any insects around any of my plants, I inspected this one before writing the post to make sure it didn't look like scale or any other kind of insect damage I'm familiar with. That's not to say there isn't insect damage I'm not familiar with! If I can try to describe the damage: the discoloration goes all the way through the leaf to the other side, and it's a little sunken in, but not completely translucent in those spots. It only appears to be on a few leaves of the oldest new cane. Even the oldest leaf on one of the older canes is completely unharmed. I do see a few tiny dark spots on the very newest leaves of the newest canes....which now concerns me. Should I spray this with something? Ack, now I'm worried!
This lives in close proximity to my other plants and I haven't noticed any problems with those... (phew)

[Dorsetman]

Maybe just try wiping the leaves with clean cotton wool balls, moistened, and look and see if there is any discoloration of the cotton wool ( pink means false red spider mite) and so on... a prophylactic spray with a bug killer won't hurt either.

[TwoStems]

Well, I unpotted it today and found a lot of dead roots, but no sign of pests. I wiped under the leaves as you suggested Geoff but there wasn't any discoloration. I repotted in a deeper pot and will be more careful about watering. I think most of the problem was over watering, but I'm still unsure what caused the discoloration on the leaves... When I unpotted it, the canes kind of separated themselves into two sets of new and old growth. I repotted them together, but could I have separated them like one would separate p-bulbs to get new plants?
I've attached some photos of the roots and the plant's new home.

[Dorsetman]

The ones in your hand include some live ones, which have got broken off in the process of repotting ( the white ones) as well as some dead ones. The ones left on your plant are live.
You are growing in what is generically described ( over here, at least) as "baked clay pebbles" which are sold under various different trade names - e.g. Hydroleca, or Leca - one supplier I buy from tells me he gets them fro five different makers in Europe under as many different names..... Your plant is in a ceramic pot ? Glazed ? With no drainage ? Then you need about 1/2 inch of water in the bottom. This will keep the roots just wet enough , by capillary action.Much more will lead to rot especially of roots permanently in water - they are not bog plants ! That level is difficult to achieve, since you can't see the water level !
Or is there a conventional flower pot in there, with the ceramic just for show ? In which case you can lift the flower pot out, check the level, replace with fresh occasionally, and so on.
You might consider fixing a stake , tie-ing it to the wall of the pot , and then tie-ing the plant to the stake ; If the plant can wobble, or be knocked, the roots move through the pebbles, and the growing tips are very sensitive, easily damaged.

[TwoStems]

Yes, the photo is misleading - it's potted in a plastic pot with sufficient drainage holes and a decent amount of space between the bottom of it and the decorative ceramic pot. It used to be in a plastic pot sold specifically for s/h with the water gauge and all, but I needed something deeper and didn't have other s/h pots. I am able to check the water level easily by lifting the interior pot out, and it's translucent so I can see the moisture level. Once I took these photos I did stake one of the older canes to keep it from wobbling around.
I know it's generally suggested to keep newly potted plants in a shadier area for awhile while the acclimate to their new home, so right now it's on my kitchen counter where it gets indirect sun. Should I move it or was this the right step to take?
I was surprised to see that the newer growths look more like keikis at the very bottom of the plant but I suppose dens are like that? I did have one keiki from this plant awhile back, but I don't think I kept it moist enough and eventually it died :/

Thanks for all your help so far Geoff This is the only den I have so I'm not super familiar with growing them

[catttan]

Geoff has given you excellent advice. The 'affliction' looks like spider mites infestation.

[TwoStems]

If they were here, they're gone now. I haven't found any evidence of live spider mites (never saw any webbing either) on any of my plants. I've had them before on non-orchids and it's no fun to clean up! Unusual for them not to stick around though, isn't it?

[opaline]

Yeuucchhh!!!!!! Spidermites- we have a long history of blood sweat and my tears. As they respond to envronment hotter/ drier = breed faster, cooler/ humid = slow down. Cymbidiums are always the first to show these critters presence in this corner of the orchid forum. Used a product imported from us 'forbid 4F' some new chemical genius spiromefesin, CPs hated it but worked and no other phytotoxicity probs or re infestations. The sp mites will colonise/ hibernate in dead matter like old sheaths regardless of environment conditions/ season so dont think theyve gone that easy.

Also from a mitekillchid victim point of view as you have focused on dends. More a pre-empt but tissue damage to plant cell membranes leaves plant open to bacterial/ fungal infections and can be similar to that of your dend naturally aborting its old cane but obviously on a larger tissue damage scale. If mites are still outandabout i would consider a fungicide spray care regime at regular intervals so the plant is armed ready for exposure if mites attack. Have noticed these work in close proximity to each other. Have found dends to be prone to bact/fungal infection and certainly high on the menu for mites. Its a conspiracy. Rose care products (bayer) cheap and cheerful work great although maybe over enthusiastic for one plants well being when theres a soapy dishcloth in the sink.