- Botrytis: Occasionally, when aeration is insufficient during forcing, Botrytis may cause lesions on foliage and cripple the expansion of leaves. Good cultural conditions prevent this problem.
- Tulip fire (Botrytis tulipae): Foliar lesions on tulip may be caused by a host-specific species of Botrytis introduced within sclerotia on diseased bulbs. Destroy infected plants and protect others with appropriate fungicides during foliage expansion.
- Iris ink disease (Mystrosporium adustum): Scales are blackened. Destroy bulbs in which fleshy scales are affected. Not common in North America.
- Bulb rots (Penicillium sp., etc.): Portions of bulbs are discolored, most often resulting from invasion of stressed tissue by weak pathogens. Avoid bruising or overheating during handling or storage. Phytophthora spp. may cause rotting of the stem, basal plate, and roots; bulb scales are not affected.
- Gray bulb rot (Sclerotium tuliparum): A dry rot with sclerotia sometimes evident.
- Flower break or mosaic: Interruption of flower petal color by white streaks or yellow mottling of foliage. Caused by virus infections. Aphid control is important for preventing spread.