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  #1  
Old 10-15-2018, 11:49 PM
SundayGardener SundayGardener is offline
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Too much light?
Default Too much light?

Hello,

I recently noticed spotting on one of my "Aussie" Dendrobiums. I've attached a picture of the front and a picture of the back of the leaves in question, as well as a picture of leaves on other, shorter canes.

Is this sunburn, or too much exposure to light? Or something else? I had it sitting on a vase so that it was closer to T5HO lights, but have lowered it again.

As an aside, I seem to have a lot of spotting on an ongoing basis on all my Dendrobiums (which are all latouria types, except 2 Australian varieties from SVO, which have not been prone to spotting until this very recent development). I have been watering the latouria types daily all summer, but I think it is time to back off on that. Are dark spots normal for Dendrobiums? (I know they seem common on Oncidiums) If not, what should I be doing differently?

Thanks for any and all info and thoughts!
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Too much light?-aussie-den-front-jpg   Too much light?-den-aussie-normal-jpg   Too much light?-den-aussie-jpg  
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  #2  
Old 10-16-2018, 02:26 AM
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King_of_orchid_growing:) King_of_orchid_growing:) is offline
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Can you please provide more information?

If this is a hybrid, what is the section of Dendrobium this is in? I'm guessing it is in Section Dendrocoryne, (the section in which Dendrobium kingianum and Dendrobium speciosum are in).

It would help to narrow down what yours is to at least the section of Dendrobium.

How are you growing this orchid?

That spotting is not normal.

It is definitely not a sign of too much light.

Do you have a spider mite problem?
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  #3  
Old 10-16-2018, 11:11 AM
SundayGardener SundayGardener is offline
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SPIDER MITES?! Ugh!

This is a Sunset Valley Orchid Australian Dendrobium hybrid, having origins I believe in Australian Denbrobium species. I think this one has Den. speciosum in it. According to SVO, they do well in a range of conditions.

So spider mites. Every incoming orchid gets pre-emptively treated with Bayer systemic but I've had this one for a year. After last year's Mealy Bug War, I've been far better about inspections, but I haven't dealt with spider mites in the past. It seems fall might be my nemesis season

So likely it's too late for quarantining and it's time to initiate kill tactics.
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Old 10-17-2018, 03:09 AM
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I'm not 100% sure that this is a spider mite problem, but I sure do suspect it...

Dendrobiums in the section Dendrocoryne tend to be tough as nails. They have a wide range of temperature tolerance, (36 F - 100 F). These can handle bright indirect light such as the amount that Cattleyas grow well under. Relative humidity can be moderate, (about 50% - 70%), and they will be ok. One week dry spells in the dead heat - not a problem.

The above mentioned is why I don't suspect temperature damage. I don't suspect sunburn in part due to the amount of light they like to grow under and in part due to the fact that this kind of damage just does not look like what sunburn typically looks like.

There are no visible insects on the plant, so that leaves out aphids, scale, and mealies which would be highly visible, (especially aphids).

I'm not even entirely sure if this is a problem caused by edema, because there are so many of these black spots. Usually edema does not leave this many black spots.

The only thing left I can think of is that you might have a spider mite problem you may not be aware of.
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Old 10-17-2018, 11:13 AM
SundayGardener SundayGardener is offline
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Thank you!

I'll start with a rubbing alcohol treatment and see if that stops or slows the damage. Some of the previously healthy looking leaves are now showing the same symptoms.

I did notice a nice real spider (not a mite) on the same orchid today. I don't know if spiders eat spider mites, but I hope they do, or eat whatever the menace is.

I'll also set up the humidifier. Humidity levels are at 50% so I thought I could wait, but it is just going to get drier.
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  #6  
Old 10-17-2018, 03:17 PM
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I wasn't going to chime in at first because of my far-from-expert opinion, but here are my two cents.
I have a den. delicatum (kingianum x speciosum hybrid) and I've seen various related 'aussie' dendrobiums as you call them in the nursery mine came from. Maybe it is the lighting, but the leaves of your plants look very light green/yellowish in comparison to my own and the ones I've seen. It could be that yours have a different ancestry, but maybe something to consider.

It definitely isn't sunburn, especially with that spotting pattern. It might be insect damage, though on my delicatum such damage usually shows up as local patches of whitish scratches/spotting when I keep it outside. I haven't seen black spotting. Have not had spider mites on this plant though, so I don't know what that would look like.
It could also perhaps be some kind of infection.

Apparently some plants of this type are prone to spotting (see Spots and Speciosum . . . – TheRockLilyMan) but it seems a bit too invasive on your plant to ignore. The leaves on the last photo are curling presumably because of dehydration - this could be because the damage that causes the spotting is so extensive it has damaged the leaves' internal structure, or it could be that some underlying problem is causing dehydration which attracts whatever infection or insect is causing the spotting.

Do you maybe have some close-ups of the rest of the plant? What does the base look like?

And yes, spotting is common on oncidiums, but I've never had spotting that looks like in your first photo. That doesn't look natural and seems more pitting than actual spotting.
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  #7  
Old 10-17-2018, 03:47 PM
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These are extremely susceptible to spider mites, especially in hot, dry conditions - like under T5HO fluorescent lights. There may be another issue as well, but I think you have spider mites.

Unless you use a miticide, not an insecticide, you will have mite attacks. I use 70% alcohol or dish soap in water to spray the entire plant.
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Old 10-18-2018, 11:58 AM
SundayGardener SundayGardener is offline
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I sprayed a diluted alochol mix with Dawn last night. I don't have any miticides in my arsenal and don't think I can find any locally. But I can buy 70% iso alcohol by the gallon and it's on my grocery list.

I can attach a picture of what it looked like when I first received it. It did have a few scattered black spots. And the leaves were a light green, I don't think there has been a change there. I have a different one whose leaves are darker. What it has now, on the longest cane, is very orange/red. I do water it 3x week.

I have it away from the lights, about 2 feet from a window now, so it can rest after being sprayed. Probably not necessary, but it won't hurt.
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Old 10-18-2018, 12:53 PM
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You have access to Lowe's and Amazon? Perhaps even Meijer? I know all three carry Bayer 3 in 1 spray and I know that Amazon carries Azamax. I'd look into those options. I sprayed so much with alcohol and dish soap that I actually washed the cuticle off my dens leaves. I now alternate between Azamax and 3 in 1.

I never saw webs or wiped off mites off my dens and I'm not sure I had mites, to be honest. The damage looked right but, after all the treatment, I still had others spotting. I spray every ten days with Azamax now and all seems well. I have read here that lack of watering also can cause problems similar to what you see. Just my
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Old 10-18-2018, 03:26 PM
SundayGardener SundayGardener is offline
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I always have Bayer Systemic for ornamentals. It's my go to. However, in all my internet searching about "mites on orchids" the gist was that systemics are not as effective on mites as alcohol or miticides?

I ordered Azamax after I went to the Pest discussion and saw it recommended for mites, also I already had it written on my ongoing list after it was mentioned on a thread about how to treat plants before bringing them inside (I use Bayer). I'll use the Azamax once I have it, but I wanted to stop whatever is going on. Or at least see if the alcohol works, so I have a control in place.

I do not have a magnifying glass strong enough to see the mites, but that's another thing to look into. On the other hand, some things I just don't need to see, I'll start seeing all kinds of mites everywhere and some are beneficial. I did think about predator insects as well, but I don't have a greenhouse so I don't think that would work.

I've been watering it 3x a week. The Latouria types I've been watering daily all summer (out of 4, one did develop root rot). With this den, I had the impression that a drying out period is preferred.
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