Yellow spots

[Kollba]

Hi.

First some background...
I live in the tropics so I keep my orchids outdoors in a "house" made from iron pipes and shade net (shadow net? English is not my native language...). I had to replant ALL of my orchids because I am new to orchids (6 months) and didn't know how the rainy season would affect them (and this year it was more rain and more rainy days than normal) so I got a lot of mold and rotten roots. I kept my orchids in wooden baskets but had put far too much chopped coconut in them and packed it too hard. Now I have learned that lesson...
I took out all orchids cleaned the baskets with 99% isopropanol, used hydrogen peroxide to disinfect the roots, put a thin layer of chopped coconut at the bottom of the baskets, put the orchids back and hoped for the best. I did that about one moth ago.
Many of them got yellow leaves that fell of after a while, but they are growing new roots and it looks like almost all will survive.
Also... I took out all my vandas and attched them to a piece of wood instead of returning them into baskets.
The net is said to filter out 70% of the sun but I think the truth is closer to 50%. I water them once a day with water from my own well (twice if it is hot and windy, but strong wind is rare here). I spray water on the whole plant - not only the basket and/or roots because the leaves dry very fast in this climate (except for the rainy season). I fertilize them once a week by spraying some local orchid fertilizer in the same way that I water them.
The temperature varies between 25 to 40 (max at daytime) and 12 to 25 (min at night). The highest and lowest temperatures are normally just 1-2 weeks in a year.
That was the background and now the questions:

Lately I have got some yellow spots on some (too many) of my orchids and I need help to find out the reason so I can take appropriate action.
The spots are the same on the underside of the leaves. On the orchid in pic 1, two leaves started with yellow spots and after a few weeks both leaves turned completely yellow and died.
The orchid on pic 2 has the same kind of spots but even the leaves without spots are more yellow than they normally should be.
What can the reason be?


I read somewhere that the purple color on pic 3 is caused by too much sunlight. I have about 10 orchids (not only vanda) that has purple leaves to some degree but most orchids has not. But in a way it is logical because during the rainy season it was often cloudy and now it is sunshine most of the time.


And finally the brown spots in pic 4. I think it is some kind of lice, but I do not know the english name (shield lice in swedish - yes I am a swede). If I scratch them with my finger nail they fall of and there is a yellow spot where they were stuck to the leaf. I guess poison is the only way to get rid of them, becuase it is not possible to pick them one by one down between the bulbs. I have some strong shit they use for killing termites, but I am not sure if it will also kill the plant...
On the other hand... As long as there are only a few on a leaf they don't seem to cause much damage and I guess I can never get rid of them completely.

First time adding pics so I am not sure what will happen...

[estación seca]

Welcome!

Your care and especially your English are good. I would not use peroxide on roots. It can damage them. We say "shade cloth."

The scale insects are difficult to control. They live in your environment so there is no point to using poisons. You can kill tthe adults by spraying with 70% alcohol or with dish soap 5ml in a liter of water. They will return.

Vandas with magnesium deficiency get purplish coloration during cooler weather. Rhynchostylis and Cattleyas have it normally. If that is a Vanda it's probably magnesium deficiency. If you can get epsom salts, put a spoonful in a liter of water and use that for watering. It can take months to correct.

The yellow spots are likely damage or fungus around insect bites. Fungal issues are common in humid tropical climates. If it's not seriously affecting growth I would ignore it. Not every fungus is susceptible to every fungicide, so you need to find out which fungus you have before choosing a fungicide effective on that fungus. A local orchid society may be helpful. The Motes Orchids Web site lets you sign up for a monthly newsletter that covers growing orchids in humid tropical areas. Motes discusses fungicide use.

[Orchidtinkerer]

Hey Kollba,
when did you move to Thailand? I'm just thinking emigrating from Sweden to Thailand 6 months ago will have been tricky!
But makes sense to start with orchids in such a climate. You will have a lot of figuring things out to do - most growing advice I know is for indoor growing. DirtyCoconuts grows outdoors and has just faced some of the issues you have described so maybe he can help more.

If that were an indoor grown plant I would say the purpling is just right, you want a bit of purpling, not too much. Purpling can happen from too much light but also as a result of too little Magnesium. Most of the time it is a combination of the 2, the more light a plant gets the more Nutrients it needs, magnesium deficiency shows first if it is not receiving enough and shows as purpling, lowering the light or increasing magnesium would rectify the problem, since you want high light to promote flowering it makes sense to increase magnesium and keep the light as it is.

The shield lice can very possibly be your only issue - even causing the other yellow spots. I use a strong spray that kills practically everything so cannot recommend what you use in Thailand, I'm sure someone has a remedy for shield lice. They will spread viruses from plant to plant so don't ignore them!

So I mentioned light feeding could help but the pictures indicate a possible PH issue or other water contamination.

So is there any way you can test the PH and the total dissolved solids (TDS) in your well water?

If you well is leeching a lot of calcium into the well water it can cause the PH to get too alkaline and cause a nutrient imbalance (too much of a certain Nutrient will start locking other Nutrients out) so worth checking that your well water ppm is in the range of rain water without too much else added to it (30-60ppm). The PH should be under 6.5

[SouthPark]

Originally Posted by Kollba

used hydrogen peroxide to disinfect the roots

Kollba ------ a heap of us here on the forum recommend to not use hydrogen peroxide on roots ----- as that substance can either cause a long-time growth setback for the orchid, or it can even kill the root hairs (and roots).

Somebody started this hydrogen peroxide band-wagon sometime in the past. We don't know who it was that started it. But it has led orchid growers down the 'wrong' path in my opinion. Taken them for a 'ride'. We definitely need people to get off and away from that bandwagon.

[Kollba]

Originally Posted by estación seca

The scale insects are difficult to control. They live in your environment so there is no point to using poisons. You can kill the adults by spraying with 70% alcohol or with dish soap 5ml in a liter of water. They will return.

Vandas with magnesium deficiency get purplish coloration during cooler weather. Rhynchostylis and Cattleyas have it normally. If that is a Vanda it's probably magnesium deficiency.

The Motes Orchids Web site lets you sign up for a monthly newsletter that covers growing orchids in humid tropical areas.

I read somewhere that 70%+ alcohol would hurt the plants ? I have some 70% ethyl alcohol, like many other people in these Covid times. If you say it is ok then I will try it. I do not care much about the insects as long as there are only a few on old leaves so it is not a big issue - more an annoying one...

I bought something they said were root booster but when I came home and got it translated, I found out it was 2% Mg solution so I will use it for a while and see if it makes any difference on the "red" orchids. (Thai is a terrible language, so I have given up trying to learn it...)

I will check out Motes Orchids. Thank you for your answer :-)

[estación seca]

70% alcohol doesn't damage orchid plants when sprayed. I use it for insect and mite pests.

[Kollba]

Originally Posted by Orchidtinkerer

Hey Kollba,
when did you move to Thailand? I'm just thinking emigrating from Sweden to Thailand 6 months ago will have been tricky!

DirtyCoconuts grows outdoors and has just faced some of the issues you have described so maybe he can help more.

If that were an indoor grown plant I would say the purpling is just right, you want a bit of purpling, not too much. Purpling can happen from too much light but also as a result of too little Magnesium.

The shield lice can very possibly be your only issue - even causing the other yellow spots. I use a strong spray that kills practically everything so cannot recommend what you use in Thailand,

So is there any way you can test the PH and the total dissolved solids (TDS) in your well water?
If you well is leeching a lot of calcium into the well water it can cause the PH to get too alkaline. The PH should be under 6.5

I moved here 8 years ago tomorrow 1st Dec, and the shade house is about 6 years old but it was my wife who had plants in it from the start. Evetually I thought it looked like crap because she has far too many plants to care about in our garden, so she did not have time for her orchids and other plants that want some shade. So I started by making 600 concrete tiles and laying a floor there and then I replaced all shade nets. I took all her orchids, got some from her mother, split some of them in two and then starting to buy all orchids I could find in the plant shops here. That started 6 months ago when I was finished with the floor, but the rainy season kicked my ass and taught me a lesson.
And... Thailands borders has been completely closed due to Covid-19 between March and October so there is no way I could have moved here 6 months ago :-)

I will check out Dirty Coconut.

About the lice and purple orchids, see the my answer to estación seca above. One problem with living here is that it is hard to find the right products for gardening since I live far away from the tourist places where most western people stay. I hate tourist places because I lived most of my life in one of those.

I have checked PH for my water with test papers and it is about 7. If I only had a few orchids I could probably test to lower the PH with a little vinegar or some other acid in the water, but there is no way I can handle the watering 1-2 times a day without using a water hose.

---------- Post added at 01:32 PM ---------- Previous post was at 01:26 PM ----------

Originally Posted by SouthPark

Kollba ------ a heap of us here on the forum recommend to not use hydrogen peroxide on roots ----- as that substance can either cause a long-time growth setback for the orchid, or it can even kill the root hairs (and roots).

Yep. I have understood that now after reading some threads here. Yesterday I was recommended to dilute the H2O2 to 0.5% when disinfecting roots. I don't know what else to use because I think 70% alcohol will damage the roots even more than 3% H2O2 even if it is ok to use on leaves and stem ?

---------- Post added at 01:34 PM ---------- Previous post was at 01:32 PM ----------

Originally Posted by estación seca

70% alcohol doesn't damage orchid plants when sprayed. I use it for insect and mite pests.

Thx

[SouthPark]

Kollba ----- not sure at all (me that is) about what minimum concentration of hydrogen peroxide is needed for reliably disinfecting an orchid on the outside of it. I have seen online values that are much less than the 3%, but definitely do not know whether those significantly reduced concentrations can be effective.

I was thinking that they purposely make 3% solution or higher in order to effectively do disinfecting.

Anyway, for pre-treatment of my orchids against say fungus ----- such as orchids stuck in a box for a few days or more during mailing ---- I just spray mancozeb.

For scale and mealybug and boisduval scale etc ----- I just use imidacloprid (which is not nice on bees ------ but should be ok when an orchid isn't flowering .... as bees should be ok when there's no flowers).

Just the other day, I noticed that a couple of pseudobulbs that I had overlooked ----- had white stuff ..... maybe boisduval scale. Lots of it! After spraying imidacloprid on the bulbs and leaves, and even some on the roots ....... it sent whatever they were packing. They disappeared real quick after that. The effectiveness even amazed me.

[Kollba]

Originally Posted by SouthPark

Anyway, for pre-treatment of my orchids against say fungus ----- such as orchids stuck in a box for a few days or more during mailing ---- I just spray mancozeb.

For scale and mealybug and boisduval scale etc ----- I just use imidacloprid

I just checked on lazada.com (thai internet shopping) and with some help from Google Translate I found both of them.
The hardest part is to know the names of the products you need and the second hardest is to find them if their names are written in thai.
Thank you for giving me the names and telling me how you are using them !!

---------- Post added at 04:07 PM ---------- Previous post was at 03:59 PM ----------

Just for fun...
Google translate can sometimes be a bit strange. This is a part of the description for Imidacloprid translated from thai:

"It is an absorbable insecticide. Effectively eradicates both dead and eating insects by destroying the central nervous system of insects."

Must be very good since it also eradicates dead insects...