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microfungus
Let's expand this to include other orchids. Some (not all!) of our plants
have a mottled color on the leaves, darker/lighter green. Thick leafed Catts and some Dends are showing this. Flowering is normal. This does not look like a fungus in any way, nor does it appear to be a virus. The leaves do not drop, nor do they develop sunken spots. I initially attributed this to drops in temperature last winter, but I'm seeing it more. (No severe temp changes down here in many months.) I haven't changed feeding regimens; we use Peters 20/20/20 w/micronutrients. I am not seeing this condition on our Oncidium types. The only two Phals that seem to be affected are a lueddemanniana and a tetraspis, and those spots really could be left over from the Mite situation. So, it's possible that what's causing this is a nutritional deficiency? How would one determine what's missing? Diana "al" wrote in message news:Z22Og.3723$xh3.848@trnddc01... one *guess* as to the pale chlorotic blotches on thin leaved Phals would be what Christenson says in his book on page 29, the last paragraph about "leaves": "The leaves of many species of subgenus Polychilos show mosaic patterning of several more or less pallid green shades that may be a result of nutritional deficiencies in cultivation. Species related to P. lueddemanniana, in particular, typically produce foliage mottled with minute sectors of paler green coloration. Although falsely attributed to a "possible" virus, the cause of this mottling is unknown. Specific studies should be undertaken to ascertain the possibility of calcium or other mineral deficiency in this species cluster." When ever I see this on my thin leaved Phals I think it could also be an internal "systemic" patch of fugal infection. I have even wondered if this is something that might be attributed to what my botany teacher called MLOs so when I read Christenson's paragraph I found it to be a of relief sorts, I thought, "so it may be normal for the species under stress and may be a nutritional deficiency." The buzz words "silvery areas with collapsing tissue" indicate a mite infection to me, especially on Phals. At least that's what I would treat for first. I like a miticide called "Ovation" It's stains everything the unmixed chemical touches a pretty pink color so you know when you have inadvertently smeared it on things like fingers and drinking cups but it is known to kill all growth stages down to the eggs. P.S., if you ARE discovering pink stains on things, you should reveiw the section of the label that talks about appropriate protective gear when handling this chemical. The common name for Tenuipalpus pacificus is "Phalaenopsis mite" but there is a Tenuipalpus species called T. orchidarum I saw mentioned recently someplace. I think that is suppose to indicate it lives on orchids. The mites from the genus Tenuipalpus are called 'flat mites". I don't think they make webs like the ones in the genus that contains 'spider' mites. I also think they are about 1/2 to 1/4 the size of spider mites, so they are tiny and flat and live in the very small depressions that they create from feeding and tend not to move around much. You need a loop (okay, a loupe) to see them clearly, unless you have a whole lot of them in which case you probably found the symptoms first, "silvery bumpy areas followed by tissue collapse. A heavy mite infestation is almost surely accompanied by secondary injury from opportunistic fungi and bacteria that enter the plant through the damage caused by the mites feeding on the weakend plant. In my experiance I have not found that 'shake the leaf over a white sheet of paper' trick to work well with the very tiny mites, but maybe that's just me. Its pretty fool proof with spider mites, if you have enough of them. "danny" wrote in message .. . I get yellow chlorosis on quite a few of my thinner-leaved phals, without any other symptoms. Anyone know what may cause that? It doesn't seem to seriously harm the plant. I also get silvery areas with collapsing tissue on the bottoms and bases of leaves of all types of phals, which tends to stop progressing if I hit them with miticides, so I assume that is just mite damage (which mites hit the phals? I can't see them. They must be a lot smaller than the spider mites on the catasetums.) -danny |