Tuesday, January 25, 2011

More fungi...?

Our Rhychostylis coelestis seems to have some kind of fungus growing on a few of it's leaves. Yesterday, I decided enough was enough as it seemed to be spreading. I sterilised some scissors in something called "Grovisan", which is apparently similar to Physan. I then cut the three dodgy looking leaves off, dusted the ends of the cut with sulphur, and sprayed the whole plant with a fungicidal spray consisting of 1ml of Benlate, 1ml of Previcur and 1ml of a wetting agent called Bladbuff. I then re-dusted the ends of the cuts with sulphur, as the spray washed some of it away. I even dumped the dodgy leaves in Grovisan (and re-soaked the scissors) before tossing the leaves in the bin.

Here's what the dubious leaves looked like: 
Closeup of the worst affected leaf; this was "weeping" fluid just after I cut it.
Underneath the leaves.
Upper side of the leaves. Note the top one has a long "blister" spreading out from the dark spot.
This plant had some Captab or Dithane (4g/l WP; actual concentration 2g/l) - I can't recall which one was sprayed on it a few weeks ago, but that didn't seem to really stop it. We used to spray the leaves of all the plants a few times a day (never in the late afternoon/evening though) to "increase humidity" in the balcony, but I've decided this is a bad idea. We'll now just be spraying the exposed roots of the Ascocentrum and this Rhynchostylis rather than the whole plant. Hopefully, this will minimise the chances of any fungal or bacterial rots. With a mist humidifier, we should be able to keep the humidity in a range where the orchids will be happy without spraying the leaves with water. On really hot days, we may still spray whole plants, but we'll see how it goes!

I really really hope this is a fungus, not a bacterium, as those seem much harder to treat (and I don't think I have, or can easily get, anything that does).