vanda leaf spot

[palito]

Howdy Everyone

Does anyone have experience with vanda leaf spot or "Thai disease". I can't find much info online other than it's a series of purple spots with diamond patterns and it's caused by the fungus Guignardia. I am looking for fungicides that can control this particular fungus and are safe for orchids. Any ideas? I have Halt and Aliette but the labels don't mention they control this fungus.

I threw two ascocenda hybrids in the trash today because they were heavily infected but the rest of the vandas may have spores in them.

http://www.doacs.state.fl.us/pi/enpp...circ/pp258.pdf

[rmt135]

Can't you isolate the affected plant from the rest. I am afraid that the fungus may spread even further.

I do not know if the fungus you mentioned is the same as the thread mentioned below? Even if it is not, the control may be the same. You can PM Cynthia for details.

Fungal Leaf Spot Picture

[Peter T]

Have you tried Physan 20? made in the USA. I have been using it for many years and it works very well with leaf spotting on most varieties of orchids, Peter T

[digitalgate]

to control fungus, you control humidity. Lower humidity will kill the fungus. But not too
low that make the orchids dried out. Remember to provide moving air so that the spores is blown away from
the plant. Be careful now.

[jerrymeola]

This cold front moving through the area may well kill fungal spores. Fungal spores do not live through the cold.

Physan 20 is a topical algaecide and I do not find it works very well on fungus. It has some effect as a weekly preventative, but not very effective as a cure.

You want to use a systemic fungicide that goes into the plant rather than a topical.
Phyton 27 is the most common available to hobbyist. It is expensive $40-50 for a small bottle but you use very little and it will last your lifetime. Cleary3336 is a commercial fungicide that is cheaper and very effective but may not be easy to find. Subdue is very good and the most expensive $224 a qt wholesale.

Others are Banrot, Thiomyl, Natriphene and Camelot.

If you have to use a topical use it several times a week. Dithane is cheap and found most everywhere.

As to the two you have I have never used them but go on the INTERNET to their web site and see if they are systemic. They probably are not. If not use them several times a week.

All these poisons are very dangerous so be very careful in their use.

[adespo]

Could you post some pics of your plant? I just got a couple baby Ascocendas that have some little speckled spots all over them.

[Ellen]

It's normal for some Ascocendas to have little purple speckles on the leaves if grown in sufficient light.

[Cynthia, Prescott, AZ]

My recommendation is to use a systemic fungicide. Don't bother with Physan 20, unless that is all you have available until you can get one of the systemics. My best recommendation is Thiophanate methyl (Cleary's 3336, OHP6672, Bonomyl, Fertilome Halt, Daconil, Spectro90, Topsin M,.. , but check labels to be sure these names are correct), with a runner up of Phyton 27. Some other systemics are triadimefon (Baylton) and Propiconozole, which I have found more locally available. Problem is that some of these are better on some fungi than than others. Are you sure that your problem doesn't just require better culture? Spotting is usually caused by things like letting plants get too cold.