Black spots/patches on cymbidium leaves

[mexicowpants]

Hi there, hope someone can help with the diagnosis of the black spots/patches that have appeared on my cymbidium plants recently, also on a couple of my epidendrum. My guess is it's too much water -- we've had a lot of very wet and humid weather recently, and the potting medium has had a pretty tough job drying out, despite the plants being outside in the breeze and that I've been holding right back on the water -- but I'd just like to have my mind put at ease, and rule out any possibly more serious problems...

Thanks in advance!

[WhiteRabbit]

my guess would be too much water, too - tho I'm not an expert, so hopefully some others will chime in!

Do the Cym pots drain well, and not left sitting in water? I have found my big hybrid Cyms to be difficult to over-water, but then we aren't usually subject to longer periods of heavy rains and humidity ...

[LizB88]

I agree with Sonya, it seems that too much water has been sitting on the plants and not enough air flow.

My is give then a good flush with some diluted brown Listerine, do this early in the morning to give enough time for the water/Listerine to evaporate before they get any sun on them. Now this will not make the leafs look better but it will help it from spreading.
I don't think you have to worry about it being anything more than a fungus.

For the 3rd picture, it does not look like a cym to me, and if it is a type of den, I would not use the Listerine, I would clean the area with some rubbing alcohol to stop it from spreading.

-Liz-

[mexicowpants]

Originally Posted by LizB88

I agree with Sonya, it seems that too much water has been sitting on the plants and not enough air flow.

Thanks for your input, it seems I was right about it being too much water. The air flow they have is great, however - a constant breeze day and night. Curse the humidity here, rainy season sucks.

Originally Posted by LizB88

My is give then a good flush with some diluted brown Listerine

Never heard of that before now, seems we only get the blue/green stuff here in Mexico. Are there any other alternatives? We have an anti-fungal powder (Captan) which we use when transplanting / making divisions -- would that be adequate?

Originally Posted by LizB88

For the 3rd picture, it does not look like a cym to me

It's an epidendrum; we have a couple of these mildly affected, too - would rubbing alcohol be best for these, too?

Thanks ever so much for your help

[euplusia]

Had the same on my 2 Cymbidiums. Virus test was negative. I guess it is a fungus. I tried Dithane neotec and Azoxystrobin.

[estación seca]

Originally Posted by mexicowpants

(Re: Brown Listerine)
Never heard of that before now, seems we only get the blue/green stuff here in Mexico. Are there any other alternatives? We have an anti-fungal powder (Captan) which we use when transplanting / making divisions -- would that be adequate?

The antifungal in the Listerine would be the 27% ethanol. It also contains tiny amounts of other alcohols and methyl salicylate. This stuff is added to make the product bad-tasting so people won't drink it to get an ethanol buzz. This doesn't stop confirmed winos, and generic Listerine is some of the cheapest ethanol available in the US.

The eucalyptol, menthol etc. also make it smell like medicine - an example of the placebo effect. The formulations in the US show the same ingredients for the different colors.

Captan is a decent fungicide. It may wash off in the rain.

Many people use powdered cinnamon as an antifungal. I know canela is widely available in Mexico. It would also wash off in the rain.

A lot of high-rain areas in the tropics and subtropics feature many native plants with leaf damage from fungus. Often it doesn't seem to injure the plant much beyond appearance. If the spots on your plants don't progress you might want to think about whether you want to treat at all. If you decide to treat, start with less toxic treatments.

I'm even more concerned about antifungal toxicity to me than pesticide toxicity to me.

[mexicowpants]

Thanks estación seca for your answer -- the patches have been getting a little larger, so I think I'd prefer to treat with something. I understand then that any ethanol solution (not just Listerine) would work, is that correct? If so, what kind of dilution should I use?

I had also heard of cinnamon as an antifungal and, as luck would have it, we've just bought a quarter kilo of powdered cinnamon for the kitchen. One doubt about this -- how would I use it? just sprinkle the powder on the affected area, or mix with water and spray? If the latter, what kind of ratio of cinnamon to water should I be using?

Sorry for all the questions, but this is something new and a little worrying for me...

[estación seca]

Originally Posted by mexicowpants

...any ethanol solution (not just Listerine) would work, is that correct? If so, what kind of dilution should I use?

...how would I use (powdered cinnamon)? just sprinkle the powder on the affected area, or mix with water and spray?

The listerine is about 27% ethanol, so something in the range of 25%-30% should be fine. Spray it on the plant with a spray bottle or wipe the plant with a cloth or paper towel soaked in alcohol.

Cinnamon powder is dusted on the affected surface. It needs to be kept dry for a while. If the leaf gets wet, let it dry, then reapply the cinnamon.

Longer-term you have to consider how to keep the plants out of all that rain but still give them light. You don't want to be treating your plants with antifungal agents constantly. You might consider some of the systemic antifungal chemicals, which are absorbed into the plant and don't wash off. This page has lots of information and links:
Orchid Pests, Orchid Diseases

Good luck, and show us photos when it flowers.

[mexicowpants]

Originally Posted by estación seca

Longer-term you have to consider how to keep the plants out of all that rain but still give them light.

Already done -- they're outside, but under shelter where they get plenty of light and a good dose of late afternoon sun. The real issue was that it's our first year growing orchids outdoors (we ran out of space inside!), and we didn't reduce their watering regime quickly enough at the beginning of rainy season.

Thanks for your advice, gave them a cinnamon powder rub-down today.

Originally Posted by estación seca

Good luck, and show us photos when it flowers.

But of course! Don't we all love showing off our babies?!?