Diseases Amaryllis is subject to only a few diseases, but their occurrence can seriously limit production by commercial growers and home gardeners. Strict sanitation and the discarding of diseased bulbs are basic to the successful culture of amaryllis. If necessary, fungicides can be used to augment sanitary measures. As a result of cankers on one side, leaves and flower stalks grow at an angle to the main axis. Any bruise to the flower stalk will produce reddening, however, and may not be disease related.
Red blotch is favored by warm, humid conditions.
Amaryllis zineb, ferbam or captan starting with the small leaf stage and stopping at bloom time. Destroy all infected plants. This disease is transmitted by insects. Practice proper insect control. Botrytis cinerea Blighting of leaves and flowers.