Oncidium with discoloured leaves
 

Hi. Along with problems with my phalaenopsis, I also have an oncidium I would appreciate advice on. :( This plant has a healthy root system and has a couple of new pseudobulbs. However, in the last couple of days I have noticed these brown spots appearing on the leaves along with some discolouration, particularly on one leaf which has taken on a mottled appearance. Any ideas what this could be and how to treat it?
Thank you in advance, Sarah

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Are you certain these developed recently?

Oncidiums are famous for having fine brown or blackish spots here and there on the leaves. Inuries commonly develop a black spot. Many people have spots on their Oncidium leaves. It is thought to be related to temperature, humidity and/or water purity not being ideal. However, it doesn't seem to affect their growth, nor flowering.

The leaf with irregular chlorophyll patches worries me more. How are you fertilizing? Is this a newer or older leaf? Do you know the pH and mineral content of your water, from the utility company's water quality report on their Web site?

Thank you for your reply. I noticed the spots very recently but couldn't say how long they have been there. I regularly look the orchids over closely and the fact it hadn't come to my attention before makes me think they are relatively new. I could easily be wrong though if it's common in oncidium orchids! :)

Regarding the irregular chlorophyll, I have noticed it becoming more apparent in a couple of its other leaves too. As a complete beginner I have only started using fertiliser recently and have done it once so far. The leaf in the photo is an older leaf. According to utility company, water pH is soft to moderately soft.

If this is something that may pass from leaf to leaf, are there any precautionary measures I can take?

Dissolve a littlle bit of alcohol in water (proportion 1/10) and rub the underside of the leaf with a cotton embeded in that solution.
If there's a red or brown tinge it indicates spider mites.

If that's not the case, I'm inclined to any kind of mineral deficiency (Mg or Ca).
See this resource, really useful for a start.

Anyway, Oncidiums are prone to this kind of "defects" on the leaves so I wouldn't worry too much if it doesn't spread.

One final question...does is gets much light?

Oncidiums are notorious for bummy leaves. I noticed today my Sharry Baby and a couple of others have slight mottling. I don't think this is cause for alarm. My plants are healthy, if not perfect. I really would not worry.

There is a lot to read and absorb about fertilizing orchids at the First Rays Web site. Click on Free Information in the top menu. The owner of the site is Ray who posts here. A quick summary is that they do well with frequent feedings of much more dilute fertilizer than other kinds of plants like.

Thank you for all the replies :)

Regarding light, it is in a west facing window which gets moderate light. I'm wondering whether it's not getting enough?

Is the window unobstructed? Light in the UK might be very different from our areas. So, you'll need to determine how bright it is. A simple way is to use your hand. Hold it over the surface and the darker the shadow, the stronger the light. Bright light should cast a hard, clearly defined shadow. Also feel a leaf, if it feels very warm, you'll need to move it or add a fan.

The window is unobstructed but because of the direction it faced, the light never gets really bright. The plants never really get warm to the touch apart from in the height of summer (and that's if we even get sun!!) I have phalaenopsis in this window too but I'm aware oncidium prefer more light?

It depends on the parents. I have bloomed some in Phal level light and I have some of the tribe in very high light. You may need to experiment. The oncidium tribe is very complex I am finding.