Unsettling leaf spots on many orchids.

[BrassavolaStars]

Hello all,

These unwholesome spots have been appearing on the leaves of several of my plants. None of these plants have had tools shared between them (many have never even been repot ever) and these plants aren’t even near each other in the greenhouse.

What is going on? I virus tested the plant in the last picture and nothing showed up. Not even a ghost of a line. That said, I can’t say whether or not all the spots are caused by the same problem. The first two sets of spots seem possibly different than the rest.

As usual the plants are in greenhouse conditions that can get very warm. Because I’ve been having heating problems, the ventilation hasn’t been great either.

I have also had some pest problems in the form of two spot mites and boisduval scale but none of these plants seemed to have been pest targets.

The first two plants are especially unsettling. Also, it seems like it might be spreading.

[Shadeflower]

Hey brassa,
it reminds me a lot of the thrip damage I have been seeing.

Also thrips weaken plants and cause spider mite outbreaks. I only had spider mites on weakened plants this year and all of them turned out to have thrips. Of course that is no diagnosis as plants can get mites also but considering this and the spots remind me of spots I could not explain, one thing that has helped has been to get rid of the thrips. It took about 3 months. Took me a while to figure out the best way to treat them and I think fingers crossed I've tackled my problem. But I might be completely wrong. Thrip damage can show in all shapes and forms and all over the plant, some would lose roots, some would become weak, others would show spots on leaves, all very random symptoms. The one thing they all had in common was thrips and they are very good at hiding. It took me a year to finally admit to myself I had thrips...

My first instinct would be a virus and who knows maybe the thrips at mine did spread a virus but at least once I tackled the thrips all symptoms stopped appearing so if it helps that has been my experience.

There's only so many things it can be at the end of the day, haven't really seen a fungal infection like it and if it isn't a virus then it could be pests.

But bear in mind you probably have not tested for all known orchid viruses so it could still possibly be a virus that you didn't test for.

At least if it is thrips you can treat them.

[Roberta]

First thing I think of when I see chloric spots like that is scale hiding under the leaves. Doesn't look like virus, and your negative tests tend to confirm that. (And virus symptoms don't tend to suddenly appear) But some sort of sucking pest is likely doing that damage. Trick is to figure out which one, since the pesticides that get insects don't attack mites and vice versa. A hand lens to closely inspect the undersides of the leaves may give you a better look.

[BrassavolaStars]

Originally Posted by Roberta

First thing I think of when I see chloric spots like that is scale hiding under the leaves. Doesn't look like virus, and your negative tests tend to confirm that. (And virus symptoms don't tend to suddenly appear) But some sort of sucking pest is likely doing that damage. Trick is to figure out which one, since the pesticides that get insects don't attack mites and vice versa. A hand lens to closely inspect the undersides of the leaves may give you a better look.

I will have to do this scale/mite check. I will also test a few more for viruses as I only tested the one in the last photo. It seemed to happen in the really hot days of summer.

The only other thing I could think of is one of those fungal spots like guignardia/phyllosticta or cercospora.

---------- Post added at 05:22 PM ---------- Previous post was at 05:15 PM ----------

The best way to check for mites is with a hand lens?

[Roberta]

I doubt virus very much. It is much more associated with long-term failure to thrive, streaks and similar makings that go all the way through leaves. And on Catts, especially, color break on flowers. Sucking pest or fungal/bacterial problem are much more likely - especially considering the speed with which the problem developed.

---------- Post added at 02:25 PM ---------- Previous post was at 02:23 PM ----------

Originally Posted by BrassavolaStars

[/COLOR]The best way to check for mites is with a hand lens?

Yes. Sometimes you get the red streaks when you wipe leaves but not always. And they are very tiny, so you can easily miss them with the naked eye. They (and scale) hide first on the underside of leaves, the spots on the top of the leaves appear after they have sucked the juices from the back side.

[estación seca]

Because you've had an unusual spell of heat and humidity I would first think of fungal attack. Check the pest pages at the St Augustine Orchid Society Web site. If you fixed the heat and humidity problem, once you control this outbreak, this should not get worse.