Remove red blotch-infected amaryllis plants and destroy them.
Apply a fungicide containing Thiophanate-methyl to the plant in early fall, according to label instructions.
Try another method if the fungicide doesn't work. Dig up the amaryllis bulb and wipe the soil off of it. Soak it for 30 minutes in water at a temperature of 104 to 114 degrees F. Use a candy thermometer to keep track of the water's temperature.
Prevent red blotch by soaking new amaryllis bulbs, for 30 minutes, in a fungicide with thiophanate-methyl as the active ingredient. Plant the bulb immediately after soaking.