Cattleya walkeriana with black spots on leaves
 

Hi there, I've had a Cattleya walkeriana for a few months now and it seems do be doing okay. It's been putting out nice healthy roots over the last couple of months and most of the pseudobulbs are nice, fat and smooth. The plant is on a west facing window ledge, planted in medium bark, in a 9cm clay pot with 1cm holes all around it. I water the plant when the potting mix becomes just dry by sitting it in room temperature water up to pot level for about 10 minutes. I feed every other watering. I also have a small fan in the area circulating the air, but not blowing the plant directly.

The black spots started to show up a couple of weeks ago on one leaf and grew quite fast. I decided to remove the leaf with a sterilised craft knife and covered the cut area with cinnamon. Since then another couple of leaves seem to be getting the same black spots.

The spots don't seem mushy or watery but are a little sunken and they are a dark blackish purple colour. I'm pretty sure it's not sunburn as it's winter at the moment and it's pretty dull and cloudy. It's not cold though.

Does this sound like classic black spot or could it be something else? I have attached a photo.

Any help would be greatly appreciated!

Cheers.

If the leaves and the spots are not mushy I most likely would not cut them. Your plants may need some calcium. Many times catts will get black spots when they are low on calcium.

Thanks for the reply!

That's interesting, how would you suggest I provide calcium?

There are several threads on here about adding calcium. Crushed egg shells work over time but there are quicker methods for right now. Here are some threads:
http://www.orchidboard.com/community...um+eggs+shells

http://www.orchidboard.com/community...um+eggs+shells

http://www.orchidboard.com/community...um+eggs+shells

I've seen a lot less black spotting since adding a Cal/Mag supplement. I just bought it at a plant or hydroponics store and add some in with my other fertilizers in the water.

This also tends to happen when it's a little cooler than the plants like. Where they're from in Brazil winter nights may be in the 5C range, but days can go into the upper 20s C of higher.

There may be solubility issues between calcium/magnesium supplements and other fertilizers, depending to some degree on water pH. It is probably best to use them on different days and not mix them together.

Do you think a deficiency in ca or mg would cause spots to appear and grow so rapidly?

The black spot in the photo I uploaded grew by about 25% in one day.

The spot is caused by an infectious organism that may grow rapidly, not by calcium deficiency. Calcium deficiency weakens the plant and predisposes it to getting infected. It takes weeks to months of feeding calcium to replenish the plant and get it back to tip-top shape. In the mean time the plant is susceptible to further infection.

Right, okay.

Would you agree that the best thing for me to do would be to treat the plant with a systematic fungicide and at the same try to provide some additional minerals?

Thanks a lot for your input.

Pretty crappy, fungicides may affect the plant. It may be a sign of toxic chlorine or something ...

I have used craft knives to remove spots with about a cm of healthy tissue around them, leaving round holes. Then I treated the cut surface with powered cinnamon. Systemic fungicides take a while to be transported through the plant. I would treat with a systemic fungicide and with a contact fungicide.

You will need to remove the infected part of the leaf. I usually disinfect the other leaves and stems with Isopropyl alcohol to disinfect (It isn't good for the roots, though). If you do have a systemic fungicide, you could then use it as a precaution.

The calcium is utilized when the plant is building new cells so you won't see the preventative effects until there is new growth. I usually add extra calcium when my Cattleyas are sending out new growth but have eggshells mixed in with the medium to provide a steady supply. Eggshells must begin decomposing before they release Calcium so it takes some time before they prove their worth. If the old growths have had adequate calcium, they will be more resistant but, once an infection gets into a plant, the plant becomes stressed and usually it will spread into the older growths, too, if the infected part isn't removed.

Good luck!

Or you could simply point the fan closer to the plant to increase air movement and help eliminate an environment which fungus thrives. You'll need to add artificial lighting as well. This species thrives in a hot, bright, arid part of Brazil which receives very little rain during winter. If its not actively growing, don't water it.

I've never heard of chlorine (such as from tap water) causing any damage similar to this.

Calcium deficiency, and susceptibility to infection, is consistent with observations from other plants.

If you can't find a calmag supplement locally, you can provide calcium with calcium nitrate, or with gypsum (plaster of Paris) dissolved at one teaspoon per gallon.

What Isurus said. C walkeriana hates cool and dark. Hates it. Add in dampness during cool and dark and you soon won't have the plant.

I grow mine very bright and rather dry during the winter.

This past summer we had a lot of rain for an extended period and w/it came cooler than normal temps and I lost a couple of my walkerianas to something that looked very similar to your black spots. [also lost a violacea and a handful of other catts] I would cut and treat w/fungicide/disease combo product but I never did stop it and I ended up throwing the plants out because every time I turned around another one was showing the same issue. I'm not saying that what you have there is exactly what I had...so many different issues can look similar...but you might want to make sure you keep it separated from others. Be especially careful of water splashing from that one onto other plants.

The problem w/some of these "rots" is that they are in the plant tissues so cutting what appears to be the infection doesn't always stop it because it's in the vascular system and continues to spread.

Keep it on the dry side and as bright as you can get it. Good luck!

Good luck!

Thanks for the great response everyone!

Here's what I've done..

-Treated with a systematic fungicide.
-Removed the worst of the black spots and dusted the cut area with cinnamon.
-Ordered a full spectrum fluorescent light bulb which I'll put in an old desk lamp to help increase light during our dull winter days.
-Water less frequently.

Does this sound like a good plan?

Thanks again.

Good plan but still add calcium...It will prevent further problems.

Sounds good! As said previously, adding calcium (which means you have to add magnesium, both of which are typically sold together in the same bottle) will probably help too.

Just thought I'd give everyone an update!

I stuck to my plan and used a fungicide, applied a cinnamon and water paste to the black spots, used a Cal/Mag supplant and now place the plant under artificial light on particularly dull days.

The black spots have completely stopped showing up and the existing ones have sunken, dried out and don't seem to be doing anything now. I've had more root and leaf growth and I now have two flower spikes coming up!

Thanks for your help everyone.

YAY - congrats!! :Tup:

Good job.

Very cool! Lets see some pics!

If this were my plant, I would cut away the black area with a single-use single edged razor blade, and then dust the cut edge with cinnamon. If it is a fungal infection, it is probably local - for the moment. You don't want that infection to get into the rest of the plant, and cutting away the bad part (go a little into the clean tissue to be sure of getting it all) may well stop it in its tracks.