Rapid root destruction on Vanda

[Lars Kurth]

Hi,

this Winter I lost some of my large Vanda's through an infection: I am trying to figure out what it was such that I can prevent next year.

I had bought a new plant - I thin imported from Asia - in autumn last year: the plant looked well and had a good root system and had several flower stems. After flowering, the roots started too shrivel and dry out rapidly and the plant started to drop the bottom leaves. I isolated the plant, when I suspected this was a disease but was too late. Eventually until only 6 leaves were left at the top. The disease would slow and then the stem at the top would become soft and topple over. When I dissected one of the affected plants, I noticed that some of the tissue in the stem had slight purple discolouration.

Plants in the vicinity showed similar effects. Roots starting to dry rapidly and leaves shedding. Similar discoloration when cutting through the stem.

I isolated affected plants as good as I could and seemingly I managed to stop the spread of the disease as no new plants have been affected in the last two months. It seems that the disease was spread through wate droplets. I lost 5 of my favourite and large Vandas, which all had excellent root systems and grew and flowered well through previous years. Vanda's which were not affected grew well: which should exclude cultural issues. I tried to use sulfur, Dithane and Systhane all without much effect. A plant would be dead within 5-8 weeks, depending on size.

Does anybody know what this could have been? My main aim is to be able to take preventive action for the next winter. I have been trying to find an explanation on the web, but have not been successful so far.

Regards
Lars

[King_of_orchid_growing:)]

Do you know what the growing parameters are?

Temperature?
Humidity?

While this may not be quantifiable, what is the air circulation like?

Lighting?

What kind of Vanda is it?

[Lars Kurth]

Phillip,

winter temperatures in the greenhouse are between 65F and 75F. A large fan is moving the air: so good circulation. However due to the cold winter this year with hardly any sunny weather (very gloomy for months), the greenhouse was pretty much a closed system. No artificial lighting.

I had the hydrofogger on for an hour in the early morning using water that had been treated with H2O2.

Lars

[King_of_orchid_growing:)]

I think your answer is:

1. Set up lights for times like what you're experiencing now. This one is for certain, a must do.

2. I don't think treating the water with H2O2 on a regular basis is good for the plants. If you are only doing this as a result of the infection your Vandas received, then I can understand.

3. Since I don't know what your humidity is and I don't know how much fog it produces or how it works. I'm not certain what to tell you about the hydrofogger.

At the moment, based off what I'm reading, my opinion would be that you may not need it.

[Lars Kurth]

Thanks for the advice:
1) I would guess I would need to get significant artificial lighting to make a difference. Probably not possible at the moment. Too costly!

2) I am only doing this as a result of the infection. In fact I don't use the water until at least 4 hours after adding the H2O2. This will kill any germs in the water, leave the water saturated with radical oxygen and O2. The theory is that the radicals will kill any germs and reduce infection from water droplets. Doing this had no visible negative effect on any of the other plants in the greenhouse.

3) Humidity during the day is between 80-40% (highest in the morning after the hydrofogger has been running). I tend to put on the fogger such that I can reduce watering to every 3-5 days depending on weather. My greenhouse heating creates quite dry air and I found in previous years that most Vanda's go into shock (root tips stop growing) when I don't use the fogger, but they continue to grow root tips through the winter if the fogger is on for an hour a day.

In this context I wanted to mention that plants that were affected had healthy new root growth. Then some of the root tips were drying and would dry from the tip backwards. Other roots would stop growing and shrivel until all roots were affected.

[King_of_orchid_growing:)]

The only other thing I may have to add in light of the new information, is to not water during the period when you see the root tips not growing, especially when they stop growing even when all parameters are optimal.

This has drastically reduced the amount of dead roots that I get on my Vandas.

Usually, the roots stop growing around winter. Not much water is necessary during this period of time. You can pretty much focus your attention on those orchids that have roots that are growing.

My .

I think the problem with your Vandas was fungal related, quite possibly due to watering during root dormancy. And quite possibly even not enough light as well.

[Angurek]

I have this exact same problem, and I can't figure out how to make them root. I'm not sure if root production in Vandas is seasonal or not, but be it as it may, my plants refuse to put out any. Since they lose roots so readily and fail to recover them, they end up halting their growth, losing their leaves, and perishing. Every single time.

I'm very frustrated. It's not the humidity (we've got plenty here in Florida). It's not the light (I have them in a very bright spot in my growing area). It's not the water (I water the darn things every single day). It's not fungus or diseases (I tested them for viruses, and they're negative. No fungal issues on any of my Vandas). Probably not the fertilizer, either (I feed them every three weeks in the warmer months, and less in winter).

I'm trying not to give up, but I'm beginning to think that they aren't worth my time anymore.

[Gin]

I have lost a couple in the past the same way I think it is a systemic rot of some type that enters the plant system and works it's way up killing growth on the way . I don't know why it happens unless water is sitting in the leaf joint and not drying fast enough . Mine don't do a lot of root growth in the winter but take off in the spring .. Sorry i don't have a good answer for you ..

[Lars Kurth]

I think it is a systemic rot of some type that enters the plant system and works it's way up killing growth on the way

I was thinking the same: I was hoping it was possible to tie it to a specific pathogen. Problem is there is little information available.

I am not planning to replace the lost plants either: but this is mainly due to space. I still have a lot of Vandaceous seedlings and smaller plants and they will grow big at some point. And of course I lost one of my favourites: a mature Renanthera matutina which flowered with wonderful sprays every year.

Maybe it is all to do with dormant infections of plants imported from Asia, which surface when conditions are not ideal. In Europe it is near impossible to keep ideal conditions for Vanda's in winter unless one is prepared to use artificial light. Practically all the mature Vanda's in Europe are imported from Asia these days. In this case, I paid a heavy price because I saw and bought a clone of a Blue Magic type Vanda at a market stall in Amsterdam, which had 4 flower spikes and one could see that the plant had flowered from every leave axil. I just had to have a clone, which apparently was such a vigorous flowerer. Only to pay a heavy price afterwards. If I had more space, I could quarantine new plants )-:

Of course that does not explain why you have problems in Florida.

Thanks for the help anyway.

Lars

[King_of_orchid_growing:)]

The roots on all my Vandas don't grow year round. They do take a break, even when you grow them intermediate to warm all year round.

I always look at the roots and how they behave. Even Neofinetias don't grow roots all year round and they're from subtropical to temperate regions of Asia.

When the root tips are not growing I don't water them much. I only water intermittently.

The lighting that Lars has is insufficient for Vandas rot or no rot. That's irrespective to the question about rot.