Wikipedia:Reference desk/Archives/Science/2017 September 20

= September 20 =

Unknown plumeria leaf disease
Well, it's a long shot, but figured I'd ask the smartest folks I know. My plumeria plant is having leaves die off, and I have no idea what's causing it. If it's helpful, I'm pretty close to the coast in southern California. They get maybe 75% sun and I only water them when they look like they need it. The plant as a whole looks healthy, although it's growing very slowly. I've had this problem with other plants, which were also in containers on my deck. Anywho, thanks in advance! Drewmutt ( ^ᴥ^ ) talk  06:15, 20 September 2017 (UTC)


 * That looks like a problem with growing conditions, I can see no evidence of an external disease like insects or fungus. This could be a normal process where leaves mature and then fall. Is the plant being irrigated with water that may be slightly alkali, from a tap for example? Do you feed the plant regularly? Richard Avery (talk) 07:49, 20 September 2017 (UTC)
 * Thanks so much for the quick reply. It's a good question about the water, it's possible, and I have some litmus papers handy (which good Wikipedian doesn't), so I can check tomorrow. Regarding feeding, I thought the same thing, since it presents itself like a K deficiency, so I got me a nice tame 5-5-5 organic fertilizer (not opposed to non-organic, btw) with limited success. Maybe it's just the wrong season? But I would expect them to just go yellow and fall as opposed to becoming necrotic. Drewmutt ( ^ᴥ^ ) talk  08:09, 20 September 2017 (UTC)
 * I wouldn't expect dramatic results with that fertilizer, not within a few weeks. A shot of miracle gro or similar (almost) never hurts, provided you test it at 1/2 strength first, and since that has plenty of soluble K I would expect it to show faster results (of course the damaged leaves won't rejuvenate, but you should stop seeing them turn). For fun, you can easily make up a batch of your own potash. But don't just go adding all the NPK willy nilly, many of the nutrient problems are not due to lack of presence in the soil, but due to lack of availability, due wrong pH, being bound up with something else, etc. SemanticMantis (talk) 20:28, 20 September 2017 (UTC)


 * According to this, it may be a disease such as rust or black tip fungus (for which I cannot find a Wikipedia article). -- Jayron 32 10:54, 20 September 2017 (UTC)
 * If so, see Black Tip Fungus from the Valley of the Sun Plumeria Society. Alansplodge (talk) 17:03, 20 September 2017 (UTC)
 * The shape of the patterns looks far more like a deficiency (and probably K) than a rust or fungus. Andy Dingley (talk) 17:11, 20 September 2017 (UTC)
 * Yes, most plant pathogens have a more distinctive patterns, including birds-eye, stripes, etc. As for deficiencies, it also be Iron_deficiency_(plant_disorder) or Manganese_deficiency_(plant). I'd apply a light dose of organic fertilizer and test soil pH. (For those, who, like me, had a momentary lapse of nomenclature, Andy is talking about Potassium_deficiency_(plants), not Vitamin_K_deficiency ;) SemanticMantis (talk) 20:23, 20 September 2017 (UTC)
 * Iron or manganese deficiencies tend to lead to chlorosis, where cells remain viable but don't produce enough chlorophyll, so the leaves turn yellow (often away from the ribs first). Potassium causes the cell structure to fail, so cells shrivel and turn dry and brown. Fungal problems often cause black spots, but the spots are more irregular (or circular, rather than following the leaf structure) and may give damp, mushy patches. Andy Dingley (talk) 22:12, 20 September 2017 (UTC)


 * Take a look at the undersides of the leaves, using a magnifying glass. Often times you can't say anything with certainty by looking at the upper surfaces of the leaves, because the mites, whitefly, etc., are usually found on the leaf undersides. Dr Dima (talk) 23:10, 20 September 2017 (UTC)