Fungi are organisms that are found in almost all habitats and they subsist either inside or on plant tissues. They obtain nutrients from their host plant, thereby obliterating the cells of the plants. Lilies are vulnerable to numerous fungal diseases and viruses, and these have a propensity to destroy the plants in combination, rather than singly. Botrytis blight and basal rot are the two most serious diseases that affect lilies. In fact, basal rot is thought to be more dangerous, as they assault the bulbs, killing the plant by stopping their nutrient supplies. Aside from root rot and Botrytis blight, lilies are also threatened by several other fungal diseases, including blue mold, black scale disease, Cercosporella blight of foliage, rust, stump rot, Sclerotium. However, most home gardeners are usually seldom bothered by many of the last mentioned fungal diseases. In the long term, the best policy is to brutally destroy all diseased plants or even those that you suspect may have been affected by fungi, irrespective of what is responsible for their symptoms. You should know that all endeavours to revitalize sick or unhealthy lilies would normally prove to be futile.
The fungus called Fusarium oxysporum var. lilii is often found together with another fungus called Cylindrocarpon, particularly in the Netherlands. It has been found that Fusarium usually damages the Asiatic lilies, while Cylindrocarpon is a greater threat for Orientals. Generally, Fusarium forms the main microbe, while cylindrocarpon forms the secondary pathogen. Cultures that have been separated from sickened lily bulbs have show the presence of just one pathogen; normally there are two or additional. However, in North America, people consider Fusarium to be the most severe disease borne by soils and, hence, it should be treated as the main pathogen.
You can be sure that your lilies have been affected by basal rot when you notice a dark brown or chocolate rot expanding into the bulb's basal plate, eventually making the bulb become squashy and fall into pieces. The fungus usually assaults the lily bulbs via their roots, the basal plate and the scales' basal ends. Several varieties of lilies are extremely vulnerable to fungus and the bulbs continue to decompose till they disintegrate completely.
The pathogen is easily spread through the spores and it can be transmitted by the soil or the bulbs' surfaces, agricultural equipment, gardening tools or even packing crates. Once the fungus is released from the decomposing bulbs, they have the potential to survive in the garden soil for no less than three years even without having a host.
In growing plants, the common symptoms related to basal rot include stunting, the foliage turning yellow prematurely and untimely senescence or aging. All these reactions are typical to ethylene - a gas generated by the decomposing bulb tissues. In fact, lily bulbs infected by fungi have several new scale bulblets, normally on the side that have been severed. Nevertheless, such bulblets usually develop at the end of the scale that is infected and, hence, they are easily infected again. Often, the main bulb is destroyed, but subsequently it results in the formation of several masses of stem bulblets.
It is worth mentioning here that Fusarium is found in nearly all types of soils and this fungus is extremely active as well as disparaging when the soil temperatures are high and there is too much moisture in the soil, especially in the summer. This fungus is particularly prevalent in places where lilies have been cultivated for several years. This disease is not a great problem in the northern areas where the climatic conditions are cooler.
Several varieties of lilies are very vulnerable to fungal diseases, while there are some that are strongly resilient to them. The resistance of the plants to these diseases can differ depending on the soil and prevailing climatic conditions. The turgid, fleshy, soft bulbs of specific Asiatic lily hybrids like Lilium cernuum as well as its hybrids appear to have a propensity to bulb rot caused by Fusarium. In addition, apparently there is some relation between the red color of the Asiatic lily hybrids and their susceptibility to Fusarium. For instance, it has been found that lilies like "Pirate", "Cinnabar" and "Scarlet Emperor" are among the first plants to suffer from the diseases spread by Fusarium. On the other hand, lilies like "Connecticut King", "Chinook", "Pollyanna" and "Enchantment" have shown some extent of resistance to Fusarium root rot.
At the same time, it is essential for gardeners to have a better understanding about cultural controls. The first and foremost thing is that they should never plant bulbs that show the slightest sign of a fungus disease. People growing and distributing lily bulbs should undertake all possible measures to make sure that the bulbs they are planting are disinfected. This comprises propagating lilies from bulbs having clean scales, bulbils, stem bulblets and seeds. If you notice basal rot in any clump or lily bed, you should immediately lift the infected plants and destroy them. Hence, you can identify and save the scales as well as stem bulblets that are more valuable and have clean and healthy scales. In case a site is heavily infected, you should essentially replace the soil up to a depth of no less than 45 cm (18 inches). On the other hand, you may also undertake sterilization or chemical fumigation of the soil before replanting the bulbs. Replanting should be undertaken when the soil temperature is relatively high.
However, the best thing to do is to prevent the infection from occurring in the first place. In fact, there are several means by which you can achieve this. Most importantly, stay away from applying fertilizers that contain high amounts of nitrogen, for instance, ammonium salts. This is because fertilizers with high nitrogen content not only encourages soft and quick bulb growth, but also make them highly susceptible to infections. If you are applying organic fertilizers like garden compost or manure, ensure that they are properly decomposed. At the same time, ensure that you do not incorporate such organic fertilizers very deep into the soil so that they do not come close to the basal roots of lilies. On the other hand, you can use properly decayed manures as well as compost in the form of mulch. When you use such fertilizers as mulch, it offers an added advantage - it keeps the soil cool, thereby discouraging Fusarium fungus.
Aside from the use of organic fertilizers, you need to control the moisture present in the soil. It has been found that Fusarium becomes more active when the soil is low and damp. Therefore, it is important to plant lilies in sites having proper drainage. Also be careful not to over water the plants during the hot summer months.
Since acid soils may also help to promote the disease, thereby worsening the condition of the plants, it is advisable that you apply some lime to the specific soils to increase their pH. At the same time, be careful so that there is no mechanical damage to the plants during cleaning up, weeding or transplanting the lily plant and also damages caused by insect bites, for instance, the biting insects like nematodes and grubs. Any type of lesion will make it easy for the pathogens responsible for basal rot to enter the plants.
If you are residing in a place where it is difficult to control Fusarium in the open ground, it is advisable that you grow your lilies in containers and use soilless growing mix or clean soil obtained from elsewhere. Several types of lilies grow very well in large containers.
It is important to note that the elevated temperatures required for scale propagation actually promote infections by Fusarium and, as a result, the bulbs can die during their infancy. Therefore, it is vital only to scale the bulbs that are healthiest. Prior to scaling, you should wash the bulbs meticulously and, before incubation, you should also immerse the scales in a potent fungicide.
Commercial lily hybridizers need to make additional efforts to raise varieties that are especially resistant to Fusarium. This is all the more important as vital chemical controls are gradually becoming out of stock.
The fungus called Colletotrichum lilii is responsible for the black scale disease. The symptoms related to this plant disease include shallow irregular lesions that are pale brown or almost black appearing on the bulbs' external scales. The tissues that are infected by this fungus begin to shrink and eventually die. When this happens, the bulb looks very unattractive.
Blue mold is attributed to Penicillium molds along with a resulting contagion caused by Cylindrocarpon as well as other associated fungal species. This disease only occurs in bulbs that are in storage and it mainly infects their external scales. This condition usually bears some resemblance to the blemishes on a damaged apple. It has been found that this problem is especially common in lily bulbs that have been dug out early and have suffered too much mechanical damage.
The best way to avoid this problem is to be careful while digging bulbs so that their external scales are not damaged excessively. Hence, it is important to be careful while harvesting as well as processing the bulbs. In case you receive the lily bulbs with the characteristic signs of rot and blue mold, you need to remove the infected areas very carefully, provided the infection is limited to a small area. In addition, drying out the bulbs and providing them with excellent aeration will also prove to be useful. Subsequently, you can dust the bulbs with any good fungicide, for instance, Captan.
Two fungus species of Botrytis - B. cinerea and B. elliptica, are responsible for the disease called Botrytis blight or fire. These fungus species assault the parts of the plant that are above the surface of the ground. While a plant may host both the Botrytis species at the same time, B. elliptica is considered to be more devastating.
Botrytis cinerea usually thrives in places having cool temperatures and has a tendency to infect the leaves, seedpods and open flowers when the weather is cool during summers and also towards the end of fall. Often, Botrytis is considered to be the most critical disease suffered by lilies, particularly in places said to be having "Botrytis climates" - for instance hot and humid coastal areas in the Pacific Northwest or Britain's western coast. Botrytis is hardly any problem for lily growers in places having relatively arid and cold climatic conditions and low rainfall.
The fungus Botrytis survives through the winter in the form of tiny black sclerotia that developed on the leaves in the preceding season. These sclerotia produce spores, which are transported by wind and water, especially rain, and deposited on emerging foliage during spring. The first sign that your lily has been infected by Botrytis is when you notice white spots on the leaves of the plant. These spots develop into marks having the shape of teardrops on the leaves' upper surface. These marks are paler along the borders, but darker in the center. Owing to such appearance of the marks they are frequently referred to as "pheasant eye" marks. When the Botrytis attacks are severe, particularly when the weather conditions are warm and wet as well as clammy, these spots coalesce finally resulting in the collapse of the entire leaf. Eventually, the leaf rots and withers away.
Interestingly enough, the fungus does not multiply or spread internally via the plant itself. On the other hand, with the production of more spores and their rapid distribution, Botrytis keeps on appearing on newer surfaces on the same plant as well as plants in the vicinity. In cases where the infection is very severe, the fungus enters the stem, resulting in the collapse of the whole plant. What is concerning is that this fungus has the capacity to devastate the foliage very rapidly. When plants are infected by Botrytis, the flowers develop brown spots, especially where there is moisture in the atmosphere. It is believed that these brown spots are caused by Botrytis elliptica and Botrytis cinerea. However, scientists are yet to arrive at a final conclusion regarding this.
Sometimes gardeners confuse Botrytis for other problems, such as frost damage, hail damage, sun scorch, mechanical injury or serious imbalance of nutrients. In order to ascertain that the problem is actually Botrytis blight, you should examine the spots using a hand lens quite early in the morning. If you detect minute hairy fungus strands standing erect like microscopic trees, you should know that the condition is Botrytis. Therefore, be prepared to spray. In fact, what you observe through the hand lens is actually the fruiting body of the fungus that produces conidia spores - it is the phase when the disease is spread to different parts of the same plant as well as plants in the neighbourhood. When plants are harmed due to mechanical damage, hail or frost, it helps the Botrytis spores to get into the leaves more easily. When such an injury occurs to the plant, it is highly recommended that you spray the plant with a suitable fungicide.
Usually Botrytis blight is not carried by the lily bulbs that may bloom the next year provided the infection was not very severe and it did not happen in the beginning of the season.
Botrytis has several strains, as both species - B. elliptica and B. cinerea, mutate without restraint, making it very difficult to control their spread. In order to check this disease, it is important for a gardener to have a good understanding of the fungus' life cycle. Once distributed by wind and water, these spores germinate and get into the leaves via the epidermal stomates. Botrytis is unable to spread in the absence of moisture. The entire life cycle, which includes development of the spores, their release and germination take place just within 12 hours. Therefore, if you have a moderately warm and wet weather in your place for about 24 hours, it may result in extensive occurrence of Botrytis. In fact, long periods of rain, fog, frequent showers and heavy dew together with warm temperatures and moisture on the foliage provide ideal environment for Botrytis blight or "fire" to spread rapidly.
It is said that in the case of Botrytis disease, a little precaution is more worthwhile that plenty of efforts to cure the problem. Hence, it is important to spray the plants as soon as you notice the first signs of Botrytis blight, especially in places or conditions that seem to be favourable for the spread of the disease. When the growing season ends, you should get rid of the entire plant debris, and also pull out the older stems when come off without problems. In case there has been a severe infection, get rid of all debris at the earliest. At the same time, pull out or cut the stems of the remaining plants and remove the maximum number of leaves possible. Remember all these stems and leaves carry the dormant sclerotia that will come to life and spread new infection in the following spring when new shoots emerge. Ideally, you should burn the debris and not utilize it in the form of compost. It would be extremely beneficial if you apply mulch to the plants during this period. Many lily growers also spray the soil using a copper fungicide when the plants are dormant and there are no growth activities. However, it has not been proved that doing this actually eliminates the dormant or germinating spores.
Lilies may be infected with Botrytis blight when the temperature is anything between 2°C (35°F) and 24°C (75°F), especially when the weather is foggy or mild and moist. Therefore, you need to get rid of all leaves that are spotted at a time when they are wet during the morning, as this will prevent or slow down the disease from spreading further.
Last, but not the least, you ought to bear in mind that spraying is only useful when the leaves are dry. You need to be especially careful about covering the leaves' underside, because there is the place when they are infected most.
All lilies belonging to the Lilium candidum group have over wintering foliage and, hence, it is essential to watch them very cautiously. In fact, the fungus Botrytis elliptica was described taxonomically from L. candidum. It has been found that the fungus Botrytis first infects the rosettes in the fall, especially when the days are warm during winter. In this way, this fungus serves as a reservoir of contagion for various other lilies that appear in spring.
At the same time, ensure that you do not plant your lilies in an area where the air circulation is poor or in a site where the drainage is not satisfactory. Ideally, you should plant your lilies in an open, airy area and where the soil has an excellent drainage. If you plant the lilies in low lying areas that are encircles with other shrubs, trees or even buildings, it may produce a trap for Botrytis. In the same manner, avoid planting lilies in places where there is too much shade, which results in the gradual drying out of the plant surfaces. This infection does not occur in places having warm, arid and sunny weather conditions. You can also check Botrytis blight from spreading if you plant the lilies at a reasonable distance from one another.
Several varieties of lilies are extremely resilient to Botrytis. For instance, Aurelians and Orientals are much less vulnerable to this disease compared to the Asiatic lilies. In fact, Lilium lankongense as well as its numerous hybrids have demonstrated amazing resistance to Botrytis, while Lilium davidii and a number of its hybrids are especially vulnerable to this disease. Even the new tetraploid lily hybrids, which have a relatively thick epidermis, appear to be very resistant to Botrytis as well as leaf scorch.
In fact, numerous growers have never used sprays on their lilies and Botrytis may not be a significant problem for lilies in some climatic conditions. Nevertheless, it is cautioned that weather is always changeable and there may be serious infections all of a sudden, which may destroy your lilies without notice.
While gardeners in North America are never bothered by Cercosporella blight, it is considered to be a serious problem in several parts of Europe. This disease is attributed to a fungus called Cercosporella inconspicua, which is said to promote a dusty mildew infection in the primary stage of the disease. Subsequently, the plants develop brown lesions and in the final stage of the disease, their appearance usually becomes blackened as well as burned.
There are several reasons for a plant to develop root rot and these include absence of adequate soil aeration, unsatisfactory drainage and planting lilies in soils having an extremely fine texture, for instance, heavy clays. The seriousness of the condition also depends of a number of aspects, including soil temperature, the geographical area and the local fungal flora.
Root rot is attributed to many different organisms, such as Cylindrocarpon destructans, Rhizoctonia solani and Pythium splendens. All these pathogens are said to be related to this condition. In fact, lesions caused by injuries inflicted by biting insects like nematodes (Pratylenchus penetrans), also referred to as meadow nematodes, make openings in the roots for the above mentioned pathogens to enter and infect them, thereby causing rots.
The fungus Rhizoctonia is soil borne and is considered to be a mild scrounger of lily bulbs. The symptoms associated with the infection caused by this fungus include deep yellow discoloration in the region of the tiny lesions, which is attributed to fungal mycelia. These lesions occur copiously and contribute to the yellowish tint of the scales. While the harm caused to the scales by this fungus is not very significant, the lesions may turn out to be the points through which various other pathogens enter the bulb.
It is possible to eliminate Rhizoctonia provided you treat the lily bulbs by dipping them in a solution containing quintozene. This will also help to remove the yellowish tint from the scales and make the bulbs appear white again. Growing lilies in warm temperatures, particularly in greenhouses, promote the Rhizoctonia. This fungus has several strains that may turn out to be pathogens in your lilies.
You can control root rots most effectively by improving cultural practices, mainly the drainage of the soil. At the same time, you should strictly avoid over watering the plants.
The fungus Uromyces holwayi is responsible for rust disease in plants. Many consider this fungus to be a novelty than a threat. This problem can be identified by the egg-shaped rust-hued pustules that appear on the leaves' upper surface and, sometimes, even on the stems. In fact, many growers are confused by a condition similar to rust on specific lilies, especially the Oriental variety named "Journey's End". They often mistake it for rust disease. Interestingly, this plant disease is not caused by any fungal pathogen, but the symptoms associated to it are attributed to virus infection. This problem is more apparent in plants that are growing under some kind of stress, for instance, forcing plants to grow in conditions where the intensity of light is poor.