leaf decoloration, posible clorosis?

[jrguevar]

Hello
The leaf that shows in the picture belongs to a prostechea cochleata that has this leaf color for quite some time now. I fertilize every 10-15 days with a 18.18.18 solution of 1gr/lt no bugs were found in the plant (rotate between imidacloprid and piretrine almost same interval at the minimun dose). located facing north with partial shade and water everytime plant medium looks dry (by pot weight). Plant doesnt have shriveled bulbs or any noticeable root damage (actually the total opossite, first year I have such plant with good nicely formed bulbs and large roots)
One of my dendrobiums near him recently developed similar leaf patterns and now Im thinking of some type of condition far more advanced for me...
So, any suggentions on how I can procede?

[camille1585]

A few thoughts:
While you may not have insects, you may have spider mites. Do you see anything on the underside of the leaves? A god way to check for mites is wiping a damp tissue on the leaves and checking for brown/red spots on the tissue after.

What sort of water are you using? Do you know the pH if it’s tap water? If you are using a rather pure water, and your fertilizer does not have any/much trace elements, a deficiency is possible. The symptoms remind me of an iron, zinc or magnesium deficiency. Is it just that one leaf on the plant, or more general? If more general, is it first appearing on newer leaves, or older one?

Another possibility is pesticide toxicity, though it usually shows up as burn marks. Using pesticides every 10-15 days on an on-going basis (if I understood correctly) is far too much, especially for systemics like imidacloprid, which stays active in the plant for over a month. The normal recommendation for imidacloprid and other neocotinids is no more than 3-4 treatments per year… I would not use it on a preventive basis.

[jrguevar]

Thank you camille for your reply!
Forgot to say Ive also got a abermectin (dont now how to write it) to contol mites in specific. Maybe once a year I also clean all leafs on the collection with alcohol and cotton (extremely troublesome...) so mites are off. Will also consider giving more time btween pesticide aplications.
Such condition goes through all leafs but dont realy know of new ones since both plants are not showing any growth (we are moving from winter to spring)
No idea of the ph of water... dont even know how to aproach that issue, and to try nutrient defficiency how can I give those elements without going to the store?...
Thanks again!

[rbarata]

I would go for Mg deficiency.

[marcmaubert]

Originally Posted by jrguevar

Thank you camille for your reply!
Forgot to say Ive also got a abermectin (dont now how to write it) to contol mites in specific. Maybe once a year I also clean all leafs on the collection with alcohol and cotton (extremely troublesome...) so mites are off. Will also consider giving more time btween pesticide aplications.
Such condition goes through all leafs but dont realy know of new ones since both plants are not showing any growth (we are moving from winter to spring)
No idea of the ph of water... dont even know how to aproach that issue, and to try nutrient defficiency how can I give those elements without going to the store?...
Thanks again!

Using pesticides on a regular basis may cause pests to evolve resistance to them. You shouldn't use them as a preventive measure. Try using safer methods first.

Ph of the water is thought to determine the nutrient availability, if it's too acid or too basic your orchid will struggle to absorb any nutrient. There are a lot of ways to test the ph: ph meters, ph tests (you can get those in pet stores, they're made for aquariums), or you could try to make your own homemade beet ph test. https://sciencing.com/use-juice-make...e-5761692.html

Most orchids like to be in the acidic side of the spectrum, between 5.5 and 6.5, try to aim for 6.0.

And does your fertilizer contain calcium, magnesium and other micronutrients? They might be missing a little bit of those.

[estación seca]

Does your fertilizer have magnesium and iron?

[camille1585]

Originally Posted by jrguevar

Thank you camille for your reply!
Forgot to say Ive also got a abermectin (dont now how to write it) to contol mites in specific. Maybe once a year I also clean all leafs on the collection with alcohol and cotton (extremely troublesome...) so mites are off. Will also consider giving more time btween pesticide aplications.
Such condition goes through all leafs but dont realy know of new ones since both plants are not showing any growth (we are moving from winter to spring)
No idea of the ph of water... dont even know how to aproach that issue, and to try nutrient defficiency how can I give those elements without going to the store?...
Thanks again!

Do you remember if it started with the top leaves or bottom leaves? That helps narrow down what deficiency it could be. Magnesium deficiency appears first old older leaves, while iron and zinc deficiencies appear it younger leaves first.

If you are using tap water, more and more often water suppliers will put water quality reports online, so maybe that is possible for you to find. If not, pH testing strips are relatively easy to find in stores that sell supplies for aquariums.

I realize that it may be more difficult where you live, bou really need to know the pH before being able to take steps. Sometimes it's not a question of having enough of micro-elements in your water, but a problem caused by pH related blockages. Most elements are readily available to plants in water with pH values up to 7 or so, with the ideal range between 5.5 and 6.5. Iron and zinc see their uptake strongly decreased at a pH above 7.5. If your water is very alkaline, you will need to address that or else no amount of fertilizer will solve the problem. If the pH is fine, you need a more complete fertilizer.

Edit: I did some searching, and it seems that in Tegucigalpa, part of the tap water comes from the Los Laureles reservoir. The data I found are old (2004) but at the time the pH was 6.95. I don't know if water treatment affects pH. EMBALSE FEDERICO BOQUIN “LOS LAURELES” | Clima Pesca

[jrguevar]

Thank you all for your comments, it is hard to tell if it first appears from new leafs or the older ones as I wrote, but I still covers all the leafs of the plants that show this condition. The plants are a P. cochleata and a dendro nobile type which I havent completely identify yet. I looked por pH testers but only found for the acidic range. The part that has me thinking is that only these two plants from the collection show this similar leaf patterns but a good cane/bulb formation.

[rbarata]

Even if everything is ok, note that different plants have different needs of fertilizer. Maybe these two need more than the others you have.
I don't know where to find the needs for each genera but I hope someone knows it, even if only as a general info.
What are the other orchids you have without any issues?

[jrguevar]

Well, since I dont have a reliable way to find the pH of my water guess Ill just have to live with it... Ive got plenty of plants oncidiums, myrmecophylia, arundina, mormodes, sobralia, masdevalia, lophiaris, phal, dendro, catleya, and a lot more species from each. But as to what Ive been able to observe recently only these 2 cases show up like such