Problem?

denise_gwOctober 14, 2010

My PC is down, so I can't post a photo, but I thought I'd describe this "problem" (or maybe not...) and see if anyone knows what it might be. My subquintplinervis (a species that looks, to me, just like pottsii) gets these flaky, light brown, flat (not scale!) spots on the oldest leaves. It's so weird - I'll take it down and water it, see the spots, wipe them off and the next time I go to water it, there they are again! I'm pretty sure it's not a pest - I see no signs of damage. The "spots" seem to rest in the "pores" of the leaves, and it's easiest to remove them by spraying the surface with some water, then using a soft toothbrush, gently scrub the surface and - voila - they're gone. If I skip brushing them off for a few waterings, there gets to be quite a lot of them. And, as I said, they're only on the oldest leaves and, as newer leaves start to age - you know, become more succulent and less shiny - I start seeing a few of these flaky spots on them. Does ANYone have an idea of what this might be??

Denise in Omaha

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mdahms1979

Denise to me it sounds like a fungal disease called leaf scab. Do the infected spots resemble the brown scabs sometimes seen on apples? I am unsure if this is a disease of Hoyas or not but it does sound fungal in nature. You might want to try some garden fungicide and if the problem persists maybe a systemic fungicide.

Mike

    Bookmark   October 14, 2010 at 10:08AM
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pirate_girl(Zone7 NYC)

Hey Denise,

Karen here, hi. While I don't know anything about this problem, if an antifungal is what you need, what about applying some cinnamon?

I sometimes dab it on roots of things, Aloe roots, Sans. roots, re-rooting Haworthias. Perhaps applying it to the leaves might be a place to experiment?

    Bookmark   October 15, 2010 at 1:18AM
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mdahms1979

Denise I did a little searching and it appears that the leaf spotting in Hoyas is often caused by Botrytis and Rhizoctonia fungi. These fungi are very common Botrytis is most often seen in grapes, if a grape is rotten you can bet that it is Botrytis. Rhizoctonia (Rhiza = root) is a common fungi that causes damping off in seedlings and root rot in mature plants.

If you scroll down you can find the entry for Hoya carnosa. The problem still sounds more like a rust or scab but there is info on treating the problems.

Mike

Here is a link that might be useful: Fungal infections Shield Soap directory

    Bookmark   October 15, 2010 at 11:45AM
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denise_gw

Thanks for all the info, Mike. I don't know much about mildews and fungii except that they tend to appear when the humidity is too high or not enough air flow, which certainly isn't a problem where I keep this plant. The "rust" sounds about right, though I assume it's still a form of fungus? Are you suggesting a powder fungicide on the leaves? I'd like to nip it in the bud before it gets worse!

Denise in Omaha

P.S. Karen, I love the smell of cinnamon - I may be tempted to "nibble" my plant using it!

    Bookmark   October 15, 2010 at 4:39PM
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mdahms1979

Denise the way most fungal infections work is that a spore germinates on the surface of the plant or in a wound and then sends out hyphae which are little root like structures that can form hyphal mats or colonies that resemble a spiders web when seen on the surface of soil etc. When the infection is not superficial and instead is internal applying topical treatments like cinnamon or sulfur will often not cure the infection. When you see the rust spot or a mushroom what you are seeing is the reproductive body of the fungi, this body will eventually release spores. Topical treatments can help prevent the reproductive phase of the fungi but to actually cure the infection you would need to use a systemic fungicide. Some systemic insecticides also contain a fungicide but ones that do not can often be mixed with an insecticide or used alone. Many fungicides are quite toxic so you need to be careful just like when using insecticides. You could always try dusting the affected areas with garden sulfur and if the problem persists then move on to a systemic.

Mike

    Bookmark   October 15, 2010 at 7:48PM
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