Den nobile 'issues'

[Fairorchids]

In one of the nurseries where I rent space, they grow a crop of Den nobile hybrids. A few of the plants are showing signs of ??

A. Some of the plants have a marked lack of chlorophyll in the leaves.

B. Some of the plants have somewhat lighter circles on leaves, with a small dark spot in the center.

Anyone know causes (& cures)?

[Selmo]

How cold is the greenhouse? How much light? Looks like the temperature is not right or it could be to much light. May be not enough fertilizer or the ph is off. These are just guesses, diagnosis, is nearly impossible to tell from a photo. But we’ll try.

The black spots look like some kind of insect damage cause by piercing/sucking insect (spider mites) or could be a hematoma (water blister). Does the surface feel rough, bumpy? Once again, guesses.

[Fairorchids]

The greenhouse had thermostat set at 55F at the time photos were taken. We have since lowered to 48F, since we also have Cymbidium in that house.

Shade cloth did not come off till abt Nov 20th (too late for my taste).

[rbarata]

Usually nobile lose their leaves and don't mind a more or less dry winter rest. I can see your medium has sphagum. What else?

[Roberta]

Actually, I think they look pretty good for this time of year. Since I grow them outdoors, mine tend to get a bit ratty as the weather gets colder - when I start drying them out. This year they are terribly confused, since it has been very warm far longer than usual... nights are FINALLY cooling off and I'm just now starting to cut back water, to try to squeeze in at least a short rest (sort of a catnap) before they start growing again. If the greenhouse ones have been experiencing cool nights, I'd expect to see at least some leaves start to show signs of dormancy. I doubt that it is disease.

[Fairorchids]

Originally Posted by rbarata

Usually nobile lose their leaves and don't mind a more or less dry winter rest. I can see your medium has sphagum. What else?

The commercial grower (from Taiwan) grows everything in pure spaghnum in clear plastic/rubber pots, as that is what he knows from Phalaenopsis. I am trying to convince him to change for both Dendrobiums & Cymbidiums.

[estación seca]

If the greenhouse grower isn't familiar with the care information on this link, he might find it interesting:

Edit June 15 2020:
Yamamoto Dendrobiums in Japan hybridizes and produces a great number of these plants. Their Web site formerly had excellent growing information for hobbyists. Unfortunately it is no longer there. You can still look at the varieties they grow, and maybe see one very similar to yours.

I saved the page, and summarized it in a post in this thread:
Uncertain if Dendrobium is still alive

Yamamoto now has a page showing how to force Dendrobium nobile for Christmas flowering in Japan's climate. There is a lot to learn from that page, but it is intended for growers who can artificially heat and cool their greenhouses during off seasons. Note they use coconut husk for growing medium, which many orchidists would say retains too much water for orchids. For many orchids that is correct, but this is a very thirsty orchid.