Big yellow spots on leaves

[smartie2000]

spidermites........? they can get very tiny and they don't always spin webs

[justatypn]

It's a good possibility it's spidermites, the webbing will come with a severe infestation. Simply apply an insecticide soap and spray weekly for a few weeks, this will keep the orchid in sync with no baby spidermite alert goin' on. Usually these types of pest have been known to come from the supplier/vendor which is reason enough to keep your new plants away from colleciton for a few weeks. Is your growing area dry and/or hot????

[Jonatan]

Is your phal. in active growth? Cause the yellowing of the leaves could be caused by nutritient deficiencies. It's not always caused by a lack of nutrient. Nutrients can be in your substrate but just not available for the plant, it all depends on your pH. What kind of water do you use for the waterings? How many leaves on the plant, total?
Is your fertilizer water soluble and dos it contain all the micronutrients needed? Here's an exemple that I found on nutritient deficiencies.

Poor growth and a variety of complaints such as leaf discolouration can be caused by a lack of plant foods. This may be due to shortages of necessary nutrients, or because the nutrients are present but not available to the plant. The latter can be caused by incorrect pH, shortages of water or an excess of another nutrient. Generally, the key to avoiding nutrient deficiencies is to ensure that the soil is healthy and contains plenty of well rotted organic matter rather than by feeding or treating individual plants.

I hope that maybe I was a little helpful. If everything is done right then you shouldn't have any problems. Maybe one last thing would be the accumulation of too much salt in your substrate, which doesn't allow the plant to absord water as much since the it competes with the roots.

[Lagoon]

I think there is always a possibility for spider mites, nasty freeloaders!
As far as the overall coloration, I'm with Jonatan on this one. I have seen a few on my phals do this with fertilizer. I don't know which one you use but Schultz is off my orchids diet.
The small black spots look fungal or bacteria to me.

[justatypn]

Nutrients might be a clue as well, when I read your prev post on the analysis of your fert, the large range of numbers had thrown me off...sounds like the phal might be deprived of its appropriate nutrients, more of some nutrients and less of another. Which can cause an imbalance.

From the is appears the phal is in a growing stage noting the new healthy root, just wish I had the answer as to what's goin' on.

Do the other leaves look healthy? Could this be merely something as simple as the adult leaf dying off???

[Pupka]

Hi, guys

Thanks for your comments. Overall condition of my phal is okay -- it grows new leaf, roots, and a spike These two leaves are the only concern. I water it once a week, never mist, maybe I should change the fertilizer to a more balanced one, like 20-20-20 maybe? As to spidermites, I never seen them, don't know how they look like. I did notice something similar to a web, on the new young leaf. I'm not even sure if it's a web, it's really tiny and looks like teared apart. Should I continue to spray with fungicide/insecticide?

[smartie2000]

Take some white paper and smack the leaves on it. If there is anything red and very tiny they may be spidermites. You may even see them crawling around on you piece of paper. The are really really tiny!

The 'false spidermites' do not spin webs.

They are the most common houseplant pest.

[Grandma M]

Fren

What is a false spidermite?

[Jonatan]

Originally Posted by Pupka

Should I continue to spray with fungicide/insecticide?

What kind of fungicide or insectide are you using and if you can tell me the ingredients on the bottle that would be great? Have you been using it alot? Sorry for all the questions I'm just trying to make the best diagnostic.

[smartie2000]

Originally Posted by Grandma M

Fren

What is a false spidermite?

false spider mite is another species of spidermite. There are several different species. These ones don't spin webs. That's about all I know...

I found some more info here:GREENHOUSE MITES AND THEIR MANAGEMENT

False spider mites or flat mites have a longer life cycle than two-spotted spider mites; eggs are bright red and oval-shaped and are laid in clusters on both surfaces of leaves; adults are reddish with black patterns on their backs and produce no webbing; damage includes silvering of leaves, but stems are also attacked.