Help with fungus or bacterial infection?

[hypostatic]

Hey, so a couple of my plants seem to be affected by this... THING. I think it's a fungus? It causes like black spots to appear on the leaves, and it'll spread and then the leaf will turn yellow and fall off.

Here are some pics for reference:










So any ideas what it is and how to treat it?

[King_of_orchid_growing:)]

What kind of orchids are they? I noticed that these plants were purchased from Andy's Orchids, so genus and species names are required to answer your question properly. The tags in the photos are illegible, (to me).

What are the daytime and nighttime temperatures where they were placed?

What kind of light exposure are they getting?

How's the air circulation of the growing area?

It does appear to be fungal, but fungal problems are usually associated with improper care, not necessarily because of the fungus itself. So in other words, you can try to kill the fungus or fungal spores all you like, but if the plant's immune system is compromised due to stress and improper environment, they'll still pop up.

[hypostatic]

Day/night temperatures range 60F-70F

The plants are kept in an indoor mini greenhouse, with humidity averaging around 50%.

There's a 6 inch fan circulating air in the enclosure 24/7

They are receiving natural sunlight from an east facing window

The species are dendrobium fimbriatum and dendrobium unicium

[King_of_orchid_growing:)]

Den unicum can drop leaves when temperatures are low. I'd keep daytime temperature at about 75 F - 80 F right now, (spring). Night temperatures can stay at 55 F - 60 F.

Summer should ideally be at 80 F - 90 F day/60 F - 70 F night.

The temperature ranges for Den unicum should also apply to Den fimbriatum as well.

Den unicum should be grown in moderately bright indirect light.

Den fimbriatum should be grown in moderately bright indirect light to bright indirect light.

Humidity levels appear reasonable. Both species are not really terribly sensitive to humidity levels being about 50%.

How often do you water?

---------- Post added at 01:56 PM ---------- Previous post was at 01:48 PM ----------

Btw, the temps they're being grown in now are closer to being winter temps.

[hypostatic]

I water about every other day by heavily misting. the plants will be dry before i mist again

---------- Post added at 05:04 PM ---------- Previous post was at 04:58 PM ----------

OK I think I found what it is

Anthracnose
Colletotrichum & Glomerella spp.

Symptoms:
This fungal disease infects the aerial portion of the plant. The leaves are most often attacked. Leaf tips turn brown beginning at the apex and proceeding toward the base. Dark brown or light gray patches develop, sometimes as concentric rings or as numerous dark bands across the leaf. The affected area is usually sharply defined and somewhat sunken, while the remainder of the leaf appears normal. Sporing bodies develop in the infected area.

Treatment:
Systemic fungicide like thiophanate methyl (like Cleary's 3336) or protectant fungicides like Mancozeb, following label instructions. Alternate systemic and protectant fungicide use.

Thoughts?

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[King_of_orchid_growing:)]

I take you also mist the leaves as well as the roots...

I recommend either drenching the wood mount and the roots as much as possible, letting very little water to get on the leaves; or misting only the mount and the roots, again, being careful to avoid misting the leaves as much as possible.

How about fertilizer? What kind are you using, (please mention the brand, whether it's urea free or not, the N-P-K ratio, concentration, and frequency)?

---------- Post added at 02:14 PM ---------- Previous post was at 02:08 PM ----------

Like I said, if you don't change the environment that favors fungal growth and suppresses the plant's immune system, treatment with a fungicide is only a temporary solution. It can come back and destroy the plant completely.

I think that the fungal issue is real, but I think it's brought about because the temperatures are too low, making the plant believe it should go into dormancy. When the 2 species start dormancy the leaves will start to lose their chlorophyll pigments. This weakens the cells that are showing carotenoid pigments, (the yellow pigments). This opens up the opportunity for a fungal invasion. Leaves would've dropped fungus or not.

Den unicum and Den fimbriatum have winter dormancies, and it it is easy to trigger a dormancy response in these plants with the correct environmental cues.

Daylength and temperatures are those cues. With temperature being the more dominant factor.

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[hypostatic]

I aim for the roots, but the leaves usually get wet as well. They'll be dry in a few hours though.

Other than the fungus the fimbriatum at least seems to be doing really well. There's new shoots sprouting up everywhere (some of those pics are new-ish shoots that are being attacked by the fungus)

I'm using Ray's MSU-type Fertilizer, I think at 150ppm (13-3-15-8Ca-2Mg).

I spray/mist with this once a week, to every other week.

[King_of_orchid_growing:)]

Try increasing the daytime temperature and give it about a week or two to see if things improve.

---------- Post added at 02:36 PM ---------- Previous post was at 02:29 PM ----------

Tropical, intermediate to warm growing species of orchids tend to respond well to warmth. They generally have a stronger immune system than those grown cooler during their respective growing cycles. They also tend to grow faster.

[King_of_orchid_growing:)]

I just thought I'd mention this. Outward physical symptoms that plants produce as an immune response to different pathogens that produce similar types of pathogenic responses to each other are often difficult to differentiate accurately or precisely without the aid of a microscope and some training.

The plant's physical symptoms of a fungal attack from one species of fungus might look the same as the physical symptoms produced from an immune response to another species of fungus.

Unless you have a microscope and you know what you're looking at under the lens, you can't easily tell what genus or species of fungus the pathogens are.

[james mickelso]

Looks like an anthracnose infection. It is a fungus and can be gotten rid of with mancozeb or other ant-fungals.