Mounted Dendrobiums have yellowing canes . . .

[DenmanNJ]

I have a collection of Dendrobium species that are mounted and currently outdoors for the Summer. I have noticed that a few of them have yellow canes or yellowing canes, and I don't know what would have caused that.

Can anyone help me with this ?

[Roberta]

Photos would help, also IDs of the "problem children" since Dendrobium is a huge genus and with different cultural needs for the various groups, impossible to generalize.

[estación seca]

As above. A common cause is high light levels, but this is not the only cause. If so and growing conditions are otherwise OK it isn't a problem. But yellowing canes can also be a sign of real trouble.