How to know if vanda has fusarium wilt

[orchidollie]

Hello!

I have been reading a lot about fusarium wilt. One of the common indicators of fusarium is the purple ring on the stem. Also, another symptom that I've read is the yellowing and withering of the roots. Now, I just want to know how to really determine fusarium wilt in vandas without having to cut the stem and look for the purple ring.

I'm just worried because I have a vanda sanderiana that has yellowing roots. I posted about it before (Vanda Sanderiana Yellowing Roots) and followed the advice of those who replied. However, the yellowing of the roots continues and there's really no growing tips on the roots right now. I am afraid that it might be fusarium.

Please help. Thank you!

[estación seca]

I went back and reread your first post. The brown, shriveled root is dead, and you can cut them off when they look like that.

The tips of the roots are all dead. The yellowing roots are dying back from the root tips. I don't think they have fusarium wilt. I still think the problem is the change of environment, and mechanical damage.

I don't grow V. sanderiana so I don't know what it likes, but from reading, it is supposed to be less able to tolerate root damage than other Vandas. Maybe it is still recovering from the move. I also read it doesn't like to dry out. When Vanda roots dry out for too long, the tips stop growing, and the roots can die back completely.

So I would guess you might water more, and try not to let the wind bump the roots into the wall nearby.

Also, how much are you fertilizing? Vandas don't grow roots or leaves without A LOT of fertilizer. I've heard lectures from two commercial growers here in the US who have used 2-3 tablespoons / 30-45ml of dry 20-20-20 fertilizer per gallon / 3.78 liters of water for their Vandas, every 5th watering. I know for sure my seedlings hardly grow if I give them less than 2 teaspoons / 10ml of 20-20-20 per gallon. The difference in growth rate is amazing when you start fertilizing adequately.

[orchidollie]

The yellowing actually started when it rained for almost nine days without respite. My smaller sanderiana also had withering roots, but she started putting out new roots. I fertilize religiously once every week with rates according to the fertilizer packaging. I'm hoping that the bigger sanderiana will now put out new roots after an application of seaweed extract.

[estación seca]

Please keep us posted. We all learn a lot hearing how people grow orchids under different conditions.

[Bud]

The fungal pathogen Fusarium oxysporum affects a wide variety of hosts of any age. Tomato, tobacco, legumes, cucurbits, sweet potatoes and banana are a few of the most susceptible plants.This pathogen spreads in two basic ways: it spreads short distances by water splash, and by planting equipment, and long distances by infected transplants and seeds. F. oxysporum infects a healthy plant by means of mycelia or by germinating spores penetrating the plant’s root tips, root wounds, or lateral roots. The mycelium advances intracellularly through the root cortex and into the xylem. Once in the xylem, the mycelium remains exclusively in the xylem vessels and produce microconidia (asexual spores). The microconidia are able to enter into the sap stream and are transported upward. Where the flow of the sap stops the microconidia germinate. Eventually the spores and the mycelia clog the vascular vessels, which prevents the plant from up-taking and translocating nutrients. In the end the plant transpires more than it can transport, the stomata close, the leaves wilt, and the plant dies. After the plant dies the fungus invades all tissues, sporulates, and continues to infect neighboring plants.
If you have this fungus then most of the neighboring plants will have this too and spreads quickly....All your orchids will be dead in a week if you have this.

[orchidollie]

Yikes! Thanks fro the information, Bud!

Anyway, here are new photos of my sanderiana. Still yellowing and no new root growth. I'm hoping that she'll put out roots soon. My other sanderiana (a smaller) had shrivelling roots after I obtained it two or three months ago, but it has new root growth now.

[Bud]

I feel you need to feed your plant weekly weakly....even if your area is humid enough, the sanderiana in situ is constantly fed by decaying leaves and bird droppings, even your local flower shop who sell those flowers have to fertilize the plant....I see the roots are long pencil thick and there is no need to panic. You have enough roots so you can cut one tip and look if there is a pinkish ring on the root cortex if you have the fungus....but I guess not....

[SouthPark]

Originally Posted by Bud

If you have this fungus then most of the neighboring plants will have this too and spreads quickly....All your orchids will be dead in a week if you have this.

Two years later. How do the big orchid growers deal with this particular fungus? At the moment, it sounds like - once it has the foot in the door, then game over for pretty much everything nearby?

Also, interesting that our technology hasn't got a means to systematically destroy this thing, without taking out the plant(s) too. But then again, our technology isn't at the stage of handling a lot of other things too. Although, fusarium oxysporum sounds devastating.

The main question for orchid growers is --- is there a way to completely avoid/evade it? Eg. regular/occasional spraying of surfaces (soil, pot, leaves, stems) with H2O2 and other substances?

[Orchid Whisperer]

Originally Posted by SouthPark

Two years later. How do the big orchid growers deal with this particular fungus? At the moment, it sounds like - once it has the foot in the door, then game over for pretty much everything nearby?

Also, interesting that our technology hasn't got a means to systematically destroy this thing, without taking out the plant(s) too. But then again, our technology isn't at the stage of handling a lot of other things too. Although, fusarium oxysporum sounds devastating.

The main question for orchid growers is --- is there a way to completely avoid/evade it? Eg. regular/occasional spraying of surfaces (soil, pot, leaves, stems) with H2O2 and other substances?

I disagree with Bud's assessment.

The one and only plant I have ever had with Fusarium is still alive, blooms regularly, after having this problem > 25 years ago. I trimmed off the infected rhizome and took good care of it. Today I would probably add use of a systemic fungicide.

[SouthPark]

Originally Posted by Orchid Whisperer

The one and only plant I have ever had with Fusarium is still alive, blooms regularly, after having this problem > 25 years ago. I trimmed off the infected rhizome and took good care of it. Today I would probably add use of a systemic fungicide.

That relieves me a lot to hear things like that. The information seen about this fusarium oxysporum fungus gave me the shivers. Did you have orchids nearby to this one that got infected? And did you need to do any treatments or spraying on nearby orchids - if there were nearby ones? It's excellent to see good news from your encounter of it.

The general details I've seen of fusarium oxysporum and orchids (in youtube etc) are linked to times when the orchid has already been infected - leading to scalpel and surgical cutting procedures. Rarely have I seen details (or pretty much never) telling us what we could do to try stop the orchids from getting infected altogether - or at least make the chance of infection really low. Eg. rotational monthly spray of one out of a set of recommended fungicides. Rather than wait for fusarium oxysporum to strike, it'd be nice to have a way to put up some barriers against it.