Orchid Culture Questions and Answers
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Orchid Culture - Questions & Answers from This Month
by Sue Bottom, from the St. Augustine Orchid Society Newsletter
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Angraecum Leaves Come Off at Base

 

Angraecum Leaves Come Off at Base

Q. Some of my angraecums lose many leaves that come off at the base. The leaves that fall are seemingly healthy, why?  

A. I suspect water is accumulating at the base of the leaf and causing the rot. The thick angraecum leaves are so close together that unless there is really buoyant air movement, you can get this sort of rot at the base of the leaf.   (Jan-19)


Dendrobium in Sphagnum

Dendrobium in Sphagnum

Dendrobium in Sphagnum

 

White Filamentous Growth on Bark

Q. I've got snow mold growing in my pots. The mix is 60% Orchiata and 40% clay pebbles, less than 2 years old. What causes it and what can I do to get rid of it.  

A. Our go-to-guy Courtney handled this one. That does not look like the Snow Mold I “know and love” (shown in the bottom image). Snow Mold becomes hydrophobic when it forms its mats and almost peels like skin. Usually the bark it is on also feels dry even after you water. In the old days redwood chips were added to keep the pH acidic in bark mixes. Snow mold was especially a problem with fir bark as it was not very acidic even when it was decomposing. Orchiata is supposed to become very acidic as it ages.
  The white stuff looks like hyphae, indicating filamentous fungi, hence the mushroom. My guess from the photos is that the fungi is feeding on the Orchiata. I am surprised that you are getting it using rain water as the Orchiata should be acidic enough to keep fungi off.
  I like a mystery. Let’s figure out what this is. Fungi are devils to identify unless there are fruiting bodies. Send your photos (mushrooms) to the U of Fl agronomy department. They may have or know a Mycologist that can get an ID for you.
  Follow-Up Comments: The filamentous fungi is feeding on the bark, so it will ultimately decompose the mix although the grower says the mix was not decomposing after 2 years in the pot. This kind of fungus does not cover and smother the roots the way snow mold does. Snow mold poses an immediate threat to the orchid's health and this filamentous fungus does not appear to pose this same danger. The sure fire way to get rid of the fungus is to repot the orchid.   (Jan-19)


Brown Spotty Patches
Brown Spotty Patches
Brown Spotty Patches
 

Brown Spotty Patches

Q. Yesterday I picked up a few plants and now am worried that they may have problems. This Dendrobium kingianum has new growths that are blemish free, but the older leaves have these brown spotty patches. Do the cattleyas have sunburn?  

A. That kingianum seems to have one of the leaf spotting cercosporoid fungi. Remove the severely affected leaves so they won't infect the new leaves. Then you can spray with a fungicide for leaf spotting fungi. The Fungo-o-nil that you bought contains the active ingredient chlorothalonil, same as Daconil, and it is effective on leaf spotting fungi. But remember, most fungicides don't cure an infection, they prevent a plant from becoming infected, so it won't fix the problem with the older leaves. Remove and discard the leaves and then spray. These fungi also affect cattleyas, the dotting on the leaf undersides is the cercosporoid spores, but they don't seem to have as severe an impact on cattleyas as on some other genera. Spray them monthly, and when you repot, remove as much of the infected tissue as you can.   (Jan-19)


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