Lc. yellowing at the petiole?

[Pynn]

My Lc. Santa Barbara Sunset had some white mold looking stuff growing at the base of the canes on the sheaths. I guess it might have been too humid? I'm growing outdoors in my lenai in Central Florida zone 10. I peeled off the sheaths and treated with Physan, then repotted into something with a bit more airflow. All of a sudden, every leaf is yellowing at the connection to the pseudobulb, dropping, then the pseudobulbs are turning yellow. Does anyone have any insight? Thanks so much!

[estación seca]

I can't see well enough in the photo. White cottony or moldy looking areas may be scale or mealybug insects. Look up photos of those and compare.

How often are you watering? Is it outdoors or indoors? What have your temperatures been lately? Yellowing and dropping leaves like this can be caused by mealybugs or scale, too high temperatures, too much sun and not enough water.

[Pynn]

Originally Posted by estación seca

I can't see well enough in the photo. White cottony or moldy looking areas may be scale or mealybug insects. Look up photos of those and compare.

How often are you watering? Is it outdoors or indoors? What have your temperatures been lately? Yellowing and dropping leaves like this can be caused by mealybugs or scale, too high temperatures, too much sun and not enough water.

Definitely not mealybugs, possibly scale. It looked like individual pinpricks of white paint. It's all gone since the Physan, I wish I took pictures. Outdoors in a screened porch southern exposure behind 50% shadecloth. Highs are 85-95F, but the worst of summer was behind us before this all started. Watering lightly approx every other day, it's wet season so the rain isn't giving me much leeway + humidity is almost always high. The media I'm using is maybe 1/4 to 1/3 coarse perlite, so things do run dry for a day once every 3-4 days. Thanks for your input!

[estación seca]

Are your nights cooling down? This hybrid includes Laelia anceps, which doesn't do well with warm nights.

[Ray]

Physan is not an insecticide.

What I see is not “yellowing of the petiole” but rotting of the pseudobulbs. I suspect a bacterial infection has somehow been introduced.

I would remove the two yellowing bulbs, then treat the plant with a copper-based bactericide/fungicide (Physan is a topical disinfectant, not systemic like copper compounds.)