Black spot
My Blc has just contracted something. One of the leaves has a
1/4in/6mm round black spot near the tip. The tip itself has not been affected, there is some yellowing around the area, the area itself is thin and filled with necrotic tissue which looks "wrinkled". The plant is sitting in about 20-25kLux of light (where it has been for most of the summer) in a steady 22 degrees and 45-55% humidity. The humidity has started rising as winter approaches. There is less air exchange - we are regularily hitting 0C during the nights now. The only thing that has changed is that I have been redecorating the hall and there is dust more or less everywhere. Could the dust be a carrier of something? There is no visible molds where I have been working. Any idea what I should do about this? I can't get hold of any brand chemicals, but I can mix my own from whatever is used in chemistry labs if someone has a recipe. There are no labs around I can send a sample to for analysis. How do I stop this from happening again? It is on a new leaf as well. Geir - unhappy |
Black spot
Gosh, I was just reading about this last night in "Orchid Pests and
Diseases"--a small book published by AOS. Here's what it says: "Calcium deficiency is most evident on cattleyas, paphiopdilums and other orchids during the spring and summer months, when the plants are in active growth. Young, expanding leaves start turning black at the tips, and as the blackening spreads downward onto the leaf blade, it is preceded by a yellow "halo." In severe cases, in may encompass the entire leaf blade. In Cattleya, it also can cause a complete blackening and death of the developing leaf...several fertilizers used by orchid growers do not have any calcium -based units, thus calcium must be added to the medium to alleviate the problem. A light dusting of lime over the surface of the medium usually will suffice.....calcium deficiency is sometimes ovelooked because it has been called sunburn or it is confused with the damage caused by excessive use of dry fertilizer. An overfertilized cattleya will first have blackening of the younger foliage (not just the new leaf, as in calium deficiency) and possibly some of the odlder leaves as well. In severe cases, root injury and the death of the plant may ensue. Good luck! In article , Geir Harris Hedemark wrote: My Blc has just contracted something. One of the leaves has a 1/4in/6mm round black spot near the tip. The tip itself has not been affected, there is some yellowing around the area, the area itself is thin and filled with necrotic tissue which looks "wrinkled". The plant is sitting in about 20-25kLux of light (where it has been for most of the summer) in a steady 22 degrees and 45-55% humidity. The humidity has started rising as winter approaches. There is less air exchange - we are regularily hitting 0C during the nights now. The only thing that has changed is that I have been redecorating the hall and there is dust more or less everywhere. Could the dust be a carrier of something? There is no visible molds where I have been working. Any idea what I should do about this? I can't get hold of any brand chemicals, but I can mix my own from whatever is used in chemistry labs if someone has a recipe. There are no labs around I can send a sample to for analysis. How do I stop this from happening again? It is on a new leaf as well. Geir - unhappy |
Black spot
dd writes:
over the surface of the medium usually will suffice.....calcium deficiency is sometimes ovelooked because it has been called sunburn or it is confused with the damage caused by excessive use of dry fertilizer. An overfertilized cattleya will first have blackening of the younger foliage (not just the new leaf, as in calium deficiency) and possibly some of the odlder leaves as well. In severe cases, root injury and the death of the plant may ensue. Ok, no, there is no calcium in my fertilizer. So this will likely also be affecting my vandas, then? Thanks for the tip. I'll see what I can do tonight. Geir |
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