Blue Mold in Lilies, Lily Bulbs, and Other Bulbs
What is Mold?
Molds are fungi that are microscopic in size. Even though they can approximate bacteria size, molds are eukaryotic organisms. That is, their genetic material is enclosed within a specialized membrane that lies in the interior of the organism.
Molds are present in virtually every environment that has been examined. Molds grow indoors and outdoors and, depending on the species, can grow year-round, even in winter. In the natural environment, molds are important and desirable because they hasten the decomposition of organic material such as fallen leaves and dead trees. Indoors, however, mold growth is undesirable. For humans, the molds that grow indoors can be of particular concern. This is because these can cause allergic reactions in those people who are sensitive to the compounds produced by the molds. The most common indoor molds are: Cladosporium, Penicillium, Alternaria, Aspergillus, and Mucor.
Molds reproduce by releasing spores (essentially packets that contain the genetic material necessary for the formation of a new mold). These spores can float through the air and, if landing in a hospitable environment, can germinate to form a new mold. One of the essential components of a hospitable environment is moisture. The many types of mold all require a moist surface for growth.
What is Blue Mold?
Blue mold rot, is a fungal disease caused by Penicillium spp. Penicillium mold is a common soil fungus, that survives on dead or dying plant debris with secondary infection by Cylindrocarpon and related fungal species. Lily bulbs don’t have a natural protective layer and are bruised easily, which can lead to severe rot. The fungus invades the lily bulb through wounds on the bulb or decaying stem tissue. Once the fungus has invaded the bulb it grows profusely, and may sporulate on the surface of a wound, appearing as a blue-green furry coating. Optimum temperatures for fungal growth are between 70 F to 77 F, with high relative humidity.
Penicillin mold occurs only on bulbs in storage and infects mostly their outer scales where there has been harvest damage or it can indicate early signs of rot and be severe enough to destroy bulb(s). The rot develops rapidly in storage, particularly in cool, humid conditions and can pass from the storage medium to uninfected bulbs/corms/tubers. The fungus grows well at low temperatures (its cousins affect fruits in the refrigerator) and can be recognized by chocolate-brown areas throughout the scales. The bulbs may be soft or “mushy” to the touch, and covered with a blue-green mold or white fungal growth. This problem is particularly prevalent in early dug bulbs that have suffered excessive mechanical injury, insect damage, bruising, stress, or are seriously infected with basal rot or any other bulb disease.
If the bulbs are severely damaged after lifting/harvesting or seriously infected with a bulb disease or rot and left unchecked, the disease can become rampant and cause them to rot, therefore destroying the bulb(s). Some varieties are more susceptible than others, such as Oriental Hybrids. However, in slightly damaged bulbs or their scales, Penicillin mold will not harm lily bulbs and the mold will simply die upon planting and will not contaminate your soil.
Primary Plants That Are Affected
Primary plants that are affected by blue mold or Penicillin mold are: any plant that is grown from a bulb, corm, or tubor. ( i.e., onions, garlic, day lily, lilies (lilium), crocuses, cyclamens, freesias, gladioli, hyacinths, irises, narcissi (daffodils), scillas, tigridias and tulips.)
How to Prevent Blue Mold
Bulbs/corms/tubers which are damaged are more susceptible to infection through the wound, so careful handling is important, particularly when lifting and storing them. The lifted bulbs should not be exposed to direct sunlight as this can also damage them. No damaged bulbs/corms/tubers should be stored. If you are harvesting or lifting your lily bulbs for winter storage, ensure that they are thoroughly dry (by leaving on the soil surface in warm, dry weather for a few days) before storing them. Good air circulation while storing for long periods is essential! I recommended not storing them in Peat Moss. Peat Moss is very fine textured, holds moisture too well, does not allow for good air circulation and will absorb a lot of moisture from the air or surrounding conditions. It is good for shipping bulbs but not, for storing over a long period of time. Instead of Peat Moss, I recommend a slightly damp potting mix with enough vermiculite or perilite to absorb moisture and it also allows very good air circulation. Keep the storage conditions dark, cool, dry and well ventilated, to prevent the humid conditions in which this disease can spread.
How to Get Rid of Blue Mold
Extreme Cases: As stated earlier, blue mold normally is only a temporary condition unless it is feeding off a more serious condition such as basal rot, bulb rot, bruised or damaged scales and is appearing inside or between scales (you can check this by gently pulling back the tip of the scale, without detaching it from the base of the bulb, and looking inside). If this is the case, destroy any bulb that is showing extreme signs of Blue Mold. You can, however, try dipping the bulb(s) in a fungicide such as Captan or Cleary’s.
Moderate to Slightly Affected: If a bulb is showing signs of blue mold on a break or cut on a scale, then this type of condition is usually not serious and you can simply plant the bulb as is or wipe the blue mold with a damp cloth, then plant it.
The best control methods for preventing a serious infection of Blue Mold is to avoid any damage to the bulb, as this pathogen gains entry through open wounds. Make sure to properly clean and dry the lily bulbs or other bulbs prior to storage. Store the bulbs at 41 F or less with low relative humidity.
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