Black spot on Cattleya
 

Hi,

I am having issues with black spots on a Cattleya hybrid.
I've noticed that it occurs when the new leaf is emerging out of the sheath and rubs against honeydew that collects there. I've tried wiping the honeydew as often as I can and it does seem to help - but not always. This often spreads to the flower sheath and ruins the spike.

I got physan 20 today and I'm hoping a foliar application will help.

This only happens on this Cattleya hybrid and its two divisions (one growing indoors, two outdoors, same thing). This is the second year I've had this one and it's happened both years. I'm not sure if this cattleya is particularly susceptible to fungal/bacterial infection, nutritional def., or diseased (or all)? I don't think it's a nutritional deficiency since it's been growing quite vigorously.

Beyond a physan 20 application, would you recommend anything else? Thanks.

Jeff .... rather than physan, try a systematic fungicide like agri-fos, and/or cleary's 3336.

Don't worry so much about honeydew etc. In the wild, nobody is going to be rubbing off honeydew etc on orchids.

Some air-movement in the growing area, and making sure the roots and media are good ----- is beneficial. I'm assuming the roots and media are ok.

I've used a systemic fungicide, infuse (propiconazole), and a copper based one (I found at a hardware store) but it did not help. A neighbor recommended physan 20. I'll look into the two you suggested too, thanks.

Roots are media are fine. I grow this one on the dry side and it's a vigorous plant overall. I have the same issue growing this one inside or outside.

Right, I see honeydew on most of my plants but they haven't caused me any issues. I don't bother wiping them. On this particular cattleya... If there's honeydew on the sheath, it almost always turns the leaf and flower sheath black (and vice versa). I may give up on this one...

Jeff - physan is a disinfectant, but doesn't get inside the plant to do some damage to whatever is causing the trouble.

Is air-movement around the growing area ok? Got reasonable air-movement?

I think this plant lacks Calcium

I started applying cal mag when the new growths appeared, recommended dose, twice a month. not sure if that's enough.

I remember now... when I got this plant, there was a mound of off white mineral that looked like garden lime. I wasn't sure what it was so I removed the mineral clumps and repotted.

---------- Post added at 08:43 AM ---------- Previous post was at 08:36 AM ----------

I'm growing one inside next to a window that's cracked open all year long (southern California!) and the division outside on the balcony. The one outside, at least, should be getting enough air circulation.

Well, calcium should not be missing when watering plants. I think that's the problem. You need to see what pH is optimal for calcium to be assimilated.

That is not a calcium deficiency.

Calcium is needed as new cells are added and then doesn't move. If there is a deficiency, it is the newest formed tissues that are harmed, which would be the very tip of the growth. The leaf tips in the photos are fine.

Obviously nothing more than a guess, but I'd lean toward a pythium/phyophthora infection.

Jeff - when you said fungicides "didn't work", what do you mean? What was your treatment regimen and what did you see?

Damaged tissues will never be cured (i.e., repaired), so should be removed. The treatment will prevent it spreading.

Late to the party... looks like black rot to me as well (pythium). I'd cut off infected parts, dab with a cinnamon paste, then use a fungicide like Aliette on it. I've never used Aliette, but it's what AOS recommends.

Had it before, and just the the former part (cut off and put cinnamon paste on the cut.

I've been applying propiconazole (2tbsp per gal) every four months per manufacturer's recommendation and copper based fungicide to the leaves whenever I noticed honeydew or a discoloration. I've only started this since last fall.

I have been wondering if I need to apply the systemic fungicide more often since the recommendation is for soil potted plants. I assumed that if it was absorbed properly initially... the media wouldnt matter.

Since then, I've had two flushes of new growth and I'm still seeing the black spots at a similar rate as before. I have two smaller growths developing (not pictured) that are not affected but the black spots usually appear when the growths are larger. We'll see...