New root browning on paphs ?

[myxodex]

With a few of my paphs I have the following problem: the new roots coming from the base of the plant start out OK and then the growing tip goes brown and the root stops growing. Usually this means the end of this new root. This usually happens when the root is only about 1 cm (half an inch) long. What follows usually is the root slowly becomes darker spreading back up to the base of the plant ... then this black crusty growth covers the surface ... which I guess is some fungus. Mostly this doesn't lead to basal rot but surely the plants that get this are not happy.

I have only been able to come up with a few guesses as to what causes this:
(1) somehow the "chemistry" of the medium is wrong and the root tip gets "burned" ... although I tend to under-feed my plants.
(2) mites bite the root tip ... I do have mites but the only ones I've seen with my lens are the larger fast moving predatory kind ... then fungus attacks the root.
(3) some sort of black fungus attacks the roots without the help of mites ?

I'd be grateful for any suggestions.
Cheers,
Tim

 

[goldenrose]

Black crusty growth? YUK! I'd use a funicide or dragon's blood.
Watering? -are you possibility overwatering?
Water quality - what's the source of water? If your TDS is high, then even if you feel you underfertilize, it's too much, or like you said - chemistry wrong = burned roots. Do you flush the pots on a regular basis?
Need repotting?
Air movement? any fungus/rots will develope & spread without adequate air movement.

 

[Candace]

Another couple of questions. What medium are you growing in and when were your plants last repotted?

 

[myxodex]

Thanks for the replies. To answer some questions:
(1) I use rain water which is stored in a small fish tank with activated charcoal filter providing vigorous circulation and a heater to keep it approx 24C. The activated charcoal is changed every few months. I don't know the TDS of the water but it has a pH of 4.5 - 5.5.
(2) Air circulation is provided by an oscillating fan on a timer so that it is on for a few hours in each of 6 "episodes" every 24h.
(3) I use a mix of bark 50%, dynarock 40%, and chopped sphag 10%.
(4) The plants with the problem were repotted in spring this year along with others that do not have this problem.

I should point out that this problem occurs with the more tricky species: hookerae (although this had only one of 3 new roots affected), hainanense (newly acquired young plant), and a bullenianum "tortipetalum" which has produced two new roots of which only one was affected. This problem does not occur on my plants of section paphiopedilum, brachy hyrbids nor on any of my other barbata species or hybrids. I did have this problem last year with my armeniacum.

With my hainanense it appears that the affected root might lead to basal rot ... and I'm not sure we can get dragon's blood here in the UK.

On my hookerae which is producing a new growth, I noticed (with the aid of a hand lens) that there did appear to be tiny pits ... some with a small drop of clear amber/brown liquid. It is the latter observation that makes me think that the initial damage might come from pests which breach the surface defenses of the new growth.

Cheers,
Tim

 

[Heather]

The black crusty growth confuses me. Any chance we can get a photo of that?

The water pH sounds a little low to me but I don't grow those species and am not sure how acidic they like it.

However, I think you have a couple things going on. The root growth that stops just sounds like it hasn't been kept moist enough to keep growing. I have had that happen with basal roots. They just aren't kept moist enough until they can grow long enough to get down into the media. When I see a new root, I try to cover it with excess media to keep it growing.

 

[goldenrose]

Boy you're making this challenging! I must commend you for the details! Tiny pits could be a sign of spider mites but if you're using a hand lens, you should see them. I'd go for a systemic drench. I still don't like the black crusty
growth on the surface, so a fungicide would be needed. Now the BIG question what's safe on these 'tricky' species & available in the UK? Something easy, in the meantime ..... dishwashing soap/detergent, water & alcohol in a spray bottle. I would check into the availability of Dragon's Blood (Sangre de Grado), it works & it seems to be safe. Cinnamon could be a temporary substitute, yes the spice powder, sprinkle it on moistened surfaces. Keep us posted!

 

[Rick]

I see this pretty frequently when the roots start above the media, and usually attribute this to low humidity and temps, possibly excess light. I see this most often in the winter in my collection. The species you mentioned tend to come from less exposed areas of the forest, acidic mossy and mulchy substrates, and more stable worm temps.

I have been moving many of my barbata into darker more humid areas of the greenhouse with good results. The warmer loving ones are often buried under the big multiflorals.