Light patches of green on leaves
 

I just noticed that my Brassavola Nodosa and a cymbidium have areas on the leaves where the green is lighter than other areas. Both plants are growing very well, and the cymbidium is shooting out its first flower spike. Growing conditions have been consistent, although I increased watering on both about 1.5 months ago due to slightly shriveled leaves on the B Nodosa.

When I see light patches on leaves I immediately think of a virus. However, could this be an indicator of too much light for the cymbidium? The Brassavola new growth has the red spots from bright conditions, but the mature leaves do not. Incorrect fertilization techniques? Flush both with Physan 20?

Possibly insufficient magnesium. Water a couple of times with an Epsom Salts solution- 1-2 teaspoons/gal ought to be sufficient.

Physan is a topical treatment only, so will do nothing for internal infections.

Thanks Ray, I'll give it a try. btw, what do you recommend for internal infections?

Can you post a photo of the underside of the nodosa leaf?

Does it have brown patches on the underside which roughly match up with the light patches on the top.

Depending upon the plant (some are sensitive to it), I like to start with copper treatments, as they tend to be bactericides and fungicides. If the issue is a proven fungal infection, thiomyl is a decent option.

It could be an indicator of too much light, but it could be quite a few other things.

Before adding Epson salts it would be a good idea to assess the likelihood of a Magnesium deficiency. That way you won't be at risk of misdiagnosing the problem or taking up watering with Epson salts regularly when it isn't the problem.

If you are using de-mineralized water such as Reverse Osmosis (RO) or rainwater, you will have been using low-magnesium water. That would indicate a possible magnesium deficiency - unless...

If you already use a fertilizer with magnesium, such as MSU or K-Lite then a deficiency is unlikely. Check your fertilizer label.

Also, if you water with hard tap water your orchid is probably getting what it needs from the tap. To know for sure, it would be best to check a water analysis. Your local water utility may post one online.

-Keith

I use tap water. Fertilizer is 10-10-10 (nitrogen, phosphate, potash) x2 per month. Heavy flush x1 per month. I'm wondering if the fertilizer is off... All orchids growing very well, Phalaenopsis grows like a weed.

Nutrition is a combo of fertilizer and what's in your water.

What is in that?

Sorry for all the questions, but they will enable us to prove or disprove the magnesium deficiency concern.

The symptoms are consistent with magnesium, but also a lot of other things.

Unless you have very soft water. there is a good chance that the water provides sufficient magnesium and calcium, but this is not guaranteed.

What brand/kind of fertilizer do you use?

Does the fertilizer package list secondary nutrients?

Do you have hard water?
Can you get an analysis from your water utility?

IF not, your water utility either posts it or will send it to you if you request. Knowing you water is a good idea even if magnesium isn't a problem.

-Keith