Black spot on cattleya p-bulb

[Jeff214]

Black spots appeared during the day on a p-bulb of a cattleya hybrid. Wondering if this may be a fungal or bacterial infection and if you'd recommend to remove the p-bulb?

This seedling has been a vigorous grower and I have been having trouble keeping the p-bulbs plump. I have been increasing the watering frequency (and put a fan next to it to dry out quicker) and the p-bulbs have started to fatten up again. However, this may have led to rot.

I've increased my fungicide and Cal/Mg regimen and it has helped another cattleya that was suffering from black spots (and now in spike!). This one not so much...

[SouthPark]

Does the plant get slowly changing temperatures during the day and night? If the rate of temperature change is quite fast, and the overall change in temperature from one temperature to another one is relatively large, then it could just lead to cell busting - usually not fatal.

If you provide some nice gentle air-flow, and relatively slow changing temperature as the day progresses, then that could probably overcome the issue.

But if it is fungal or bacterial - then a spray of montery garden phos could be good too.

Did the patching begin as yellowing first? And is the region soft/mushy? Don't forget to wash hands etc after touching it.

[estación seca]

It's most likely sun if it's not soft and squishy. The plant looks very healthy to me. Older pseudobulbs on Cattleyas often develop spots like these. Blackening of new growth is usually inadequate watering, not fungus. Regular preventive fungicide is not a good idea.

[Jeff214]

Originally Posted by SouthPark

Does the plant get slowly changing temperatures during the day and night? If the rate of temperature change is quite fast, and the overall change in temperature from one temperature to another one is relatively large, then it could just lead to cell busting - usually not fatal.

Did the patching begin as yellowing first? And is the region soft/mushy? Don't forget to wash hands etc after touching it.

I didn't notice anything this morning and it was black this evening. The affected area isn't soft - I can't tell any difference from the healthy areas.

It has been getting hotter here and I've started to use the AC inside the home this week. I would say that there is a faster temperature fluctuation now, but... just an AC setting between 76 and 80 oF.

Originally Posted by estación seca

It's most likely sun if it's not soft and squishy. The plant looks very healthy to me. Older pseudobulbs on Cattleyas often develop spots like these. Blackening of new growth is usually inadequate watering, not fungus. Regular preventive fungicide is not a good idea.

It's been sitting under the grow light but it has been getting warmer in the house. I have the fan going only when I'm around - perhaps it's starting to overheat?

That's good to know - I didn't realize older psuedobulbs could develop black spots like this. All four of the new growths on this one are doing fine. The black spots appeared on an old growth.

I understand why preventative anti-microbial treatment may not be a good idea... Just been a little paranoid with a couple of cattleyas that have been prone to black spots. I should ease off...


Thanks for the comments. I will monitor and see if it spreads. I may just leave the fan on all day if it helps mitigate the warm temps inside my apartment.

[SouthPark]

Thanks for adding those details Jeff.

Also check to see if those circled regions are bumps on the bulb. Maybe just edema related - maybe all ok and no problem.