There is no fungicide used for treatment of Southern Blight; only preventative measures to maintain good air circulation around vulnerable plant parts (usually the crown, at the soil surface) by reducing mulch use and cleaning-up dead vegetation.

Southern Blight is not typically associated with Amaryllis or other flower bulbs. Is this plant growing outdoors or indoors? What symptoms are you seeing that suggest Southern Blight? (You can attach photos for diagnosis.)

Miri

Hello John,

Thank you for the photos, though we only received one of them. We can't identify with certainty what is causing the residue in the image (#0676), though it does not look fungal. If anything problematic (as opposed to inconsequential), it might be residue from mealybugs, which would explain why it keeps reappearing. You can inspect the nooks and crannies of the bulb base (where the foliage emerges) as well as any flower stalk and buds, if present. Look also underneath the pot rim and the pot base, as these can be other locations mealybugs like to hide when not feeding. When houseplants are put outdoors during the growing season, sometimes pests like mealybugs get eliminated by natural controls, including parasitoids and predators.

Brown soft scale is another possibility for the small brownish lumps on the foliage. (They would not cause a powdery residue, though it's possible more than one issue is present at the same time.) They are difficult to control indoors, but the simplest approach is to flake them off the plant with a fingernail or toothpick. They will not survive being removed and cannot climb back onto the plant. Although scale glue themselves onto the leaf while alive, they will come off with little effort, so if not removable without gouging the leaf, something else is causing the bumps on the leaf.

Copper-based fungicides are preventative measures only; they do not cure existing infection. Therefore, when applied to symptomatic growth, no apparent impact will be seen as any damage caused by infection will not be reversed. Plus, the plant being treated should (ideally) be included on the product label so you are assured it is tolerant of the chemicals in the spray. (Some plant species are quite sensitive and can develop phytotoxicity, which is tissue damage from the chemical exposure.) Since this does not look fungal - and is not Southern Blight - we would not expect any visible benefits from a fungicide application.

If the plants are not growing well (and if no mealybugs or scale are found), then another cause is likely. This could be moisture-related, as indoor plant issues often are, or it could be related to light levels. Indoors, the latter problem is more often too little light rather than too much, but it depends on the quality and intensity of the light source. If the plants have not been fertilized in the past growing season, they could also be suffering from a mild nutrient deficiency, though this would not be as imminently threatening to plant health compared to over-watering. Insufficient lighting also causes a slow, rather than rapid, decline. Unfortunately, paler-than-normal leaves and blotchy coloration on foliage can be caused by an array of factors, sometimes overlapping in impact, so determining which is the main cause can be difficult. Since we can't see the whole plant at present, it's hard to guess how significant its current symptoms are.

Miri