Spots on oncidium-False spider mites or ?

[Shabe]

These spots appeared on my Sharry Baby oncidium. They appear to be a central spot surrounded by sunken tissue about 2mm across. I’ve also seen these on my jumellea where they produce a sticky exudate. Mostly on the new leaves for both. I don’t see any spider mites even with 15x magnification. Pest or disease or nutrition problem?

[estación seca]

Welcome to the Orchid Board.

What are your growing conditions? Temperatures day/night, humidity, light? How and how often are you watering?

[Shabe]

I grow my orchids mostly under artificial light, with good humidity. I don’t track day/night temp - it doesn’t vary much indoors. Nor do I pay attention to how often I water. The oncidium is in sphagnum so I only water when it approaches dryness, before the moss gets hydrophobic. I fertilize every so often with a dilute cal-mag orchid fertilizer (again I don’t track how often) The plant is otherwise healthy. I just thought someone might recognize the spots as being from a specific cause.

[Dimples]

I don’t grow oncidiums but the spots sorta resemble oedema/edema I’ve seen on other plants. Do they turn black/brown/dark after a while or stay looking like that?

Unless your fertilizer is a complete formula that just advertises having more cal-mag than usual, you’ll want to start using a complete fertilizer to supply the other necessary nutrients that plants need for growth. Standard cal-mag fertilizers are typically used in rotation with a complete fertilizer (that has NPK + micro nutrients) to boost/supplement those two nutrients for plants that need it, but they don’t supply anything else to the plants.

[Shabe]

Thank you for the tips. I figure it might be Ca and Mg deficiency because some of the leaves are showing signs of Mg deficit. Although the fertilizer I use has those in it I water exclusively with distilled/rain or RO water and I’m sure I underfertilize.

[estación seca]

Cal/Mag supplements are supplements, not fertilizers. If using pure water you need to provide all the required nutrients.

[Shabe]

I use an orchid fertilizer (NPK) with micronutrients and Ca-Mg. It is fertilizer specifically for RO (not municipal) water. It doesn’t work well if not applied regularly😄 As I said I tend to underfertilize.

[estación seca]

The fertilizers with calcium and magnesium have very small amounts of both due to solubility issues with other chemicals in the fertilizer. Even with regular use that may not be enough calcium nor magnesium for some plants.