Black spots on my Vandas - best funguicide?

[marla468]

I am new to Florida and the house I purchased has beautiful orchids on several trees. I have recently noticed that many are suffering, and I am not sure why... My Vandas seem to have the Guignardia leaf spots (Orchid Diseases) I read the recommended article on "Cercospora Leaf Spot Caused by Cercospora dendrobii on Dendrobium antennatoum Lindl. and Its Control". The best recommendation is to apply a funguicide with pyraclostrobin + boscalid at a concentration of 20%WG at 226.8 g per 379 L (0.50 lb per 100 gal) of water. However, I have only found places where they sell it for commercial use and the price for this is outrageous, 30oz for $500! Do you have any other recommendations? As according to the article, one affordable funguicide, Thiomyl, has very poor results, it is almost the same as adding water to my orchid leaves!

Please let me know your suggestions on how to take care of my Vandas, the spots are invading everything!

Thank you

[estación seca]

Welcome to the Orchid Board!

As you've learned, not all fungi are susceptible to all fungicides. You need to know what fungus you're treating to pick a fungicide.

I recommend you go to the Motes Orchids Web site, and sign up for the newsletter. Each month they will mail you informationon what to do that month. You can also access the information from the Web site menu.

I would also join a local orchid society. Your new local friends will have better advice.

I think at least some of the black areas are caused by mechanical scratching, and perhaps cold damage.

[marla468]

Thank you for your reply, I have already reached out to local clubs...

[beachgirl]

I'm not as experienced as many people here, but your vanda's symptoms look similar to this:
Phyllosticta Leaf Spot so yes I think your diagnosis is right. I live in south florida too and seem to have the same problem. I am trying the thiomyl on my vanda orchid, but I had not heard it gave poor results. It is advertised as being a replacement for Cleary's 3336 with the exact same active ingredient, and I know many orchid growers use Cleary's.

By the way, I just read the article you referenced and I believe it was about the yellow spots (cercospera) not the dark ones (guignardia) if I'm not mistaken.

[marla468]

Thank you for your help!