contagious rot in Cattleya new growth
 

Hi.
recently i noticed that many of my Cattleyas have some kinda of infection in their youngest growth.
I'm cutting into clean tissue and applying cinnamon, but it keeps happening to the next growth, of several plants.
(I'm very careful, and i'm quite sure i didn't drip water on these when they sprouted)

sometimes it is clear from the start that the new knob has some dark spots on it, and is not solid green, when it grows one of the sheaths turns black, and soft.

other times, it starts from the very tip of a newest growth that is nearly mature, and slowly spreads downwards.

https://lh3.googleusercontent.com/JZ...=w718-h1277-no

https://lh3.googleusercontent.com/Va...=w718-h1277-no

https://lh3.googleusercontent.com/-j...=w1440-h810-no

https://lh3.googleusercontent.com/1W...=w1440-h810-no

They're being overwatered. That's the root cause. Reduce watering. Then the problem will remedy itself.

In the meantime, don't cut anymore leaves. If the plant is strong enough, the necrosis will stop on its own. Another possibility is that the leaves will drop, but the pseudobulbs will persist, in which case it'll still be ok because the subsequent new growth will grow out to look better.

WOW.
so you're saying it's not a bacterial rot?
i was sure the usual sign of over-watering is dehydration due to root rot.
i'll reduce watering, and report back.
i'm using the bamboo stick method now, i'll wait till it completely dries.
thanks a lot.

It is bacterial rot, but that is not the primary cause of the problem. The bacterial rot is the secondary problem, it is an opportunistic infection. That's why whenever you treat for the bacterial problem, you always continue to have the same problems. You just basically put a band-aid on the real problem which was overwatering.

It can be but not always. Sometimes the overwatering manifests in root rot that leads to dehydration if the damage to the root system is severe enough.

However, the other way it can present itself is through rotting of the new growths, pseudobulbs or leaves.

I have seen this problem multiple times and I can spot what the underlying [primary] problem is pretty quickly. Cutting back on the water produces good results fairly quick in these kinds of cases.

No problem.

With Cattleyas, they can go pretty dry and still not experience a whole lot of problems.

I'm not sure I buy "overwatering" as the cause. I grew catts in S/H culture and never saw anything like that.

Maybe you could give us a detailled description of your growing conditions: humidity, watering frequency, temp, type of medium and pot material, light, etc.

I'm only a beginner but St Augustine says it could be calcium deficiency. It looks a lot like the photos of this, anyway.

https://staugorchidsociety.org/PDF/C...ySueBottom.pdf

https://staugorchidsociety.org/PDF/2...ps-Calcium.pdf

https://staugorchidsociety.org/PDF/C...ySueBottom.pdf

thanks Benno, that actually makes a lot of sense.
the fact that the "rot" moves down the leaf, and come back despite me cutting into healthy tissue.
and the fact it moves rather slow (maybe one centimeter per month).
i'll finish reading these papers, and see how i can improve.

all my plants are sitting on a south facing windowsill (Israel), in my living room, which had air-conditioning during summer, especially on weekends.

at the beginning of summer this window was exposed to direct sunlight only in the late afternoon, so i kept the blinds open all day long, putting Catts and Den.Phals in front, and Oncidiums and Phals on the back.

in mid summer the window started to get exposed to full sunlight earlier in the day, and i had some sunburns (leaf temperatures of about 40c), so i closed the blinds half way (to slits mode).

i'm usually using rain water i collect in winter, and water from air conditioner in summer. these have about 20ppm of dissolved solids, and i'm fertilizing weekly weakly, with some generic orchid fertilizer (which i'm not sure what it contains).
i use 1/4 strength, which gives me about 200ppm.
I was soaking the the pot in water for about 20 minutes, once a week in summer, and i'll probably go to once in two weeks in winter.

during the hot summer months, the media (mostly medium bark, with some sphagnum dressing at the top), appeared to be drying up rather quickly, so in between the weekly watering, i used to spray some A/C water on the top dressing in between watering (about 2 to 3 times per week).

near the end of summer, i started using the bamboo stick method, and i did notice the stick seems to be slightly wet, and cold, even though the media appears dry.. so i might have been watering the Catts too much.

here's a photo from afternoon in early summer.
https://lh3.googleusercontent.com/IU...=w1413-h795-no

Classic calcium deficiency symptoms.

Cool. What triggers you to water, is it a schedule? If it's hot where you are, orchids in medium bark probably need proper watering more than once a week. Some of mine need it every 1-2 days at the moment where I am.