Lilies are very delicate flowering plants that are comparatively more susceptible to various pests and diseases. Compared to many garden plants, lilies succumb to diseases and pests more easily. Nevertheless, it is possible to grow lilies successfully and help the plants to exhibit an excellent show each year, provided you take proper care of the plants and be cautious while selecting the chemical fertilizers and pesticides available in the market today. What is, however, worrying and unfortunate is that today many gardeners are using chemical fungicides and pesticides needed to prevent lilies from being invaded by pests or troubled by diseases. The fact is that most of these modern chemicals are neither safe for use nor healthy for the environment.
On the other hand, employing natural means to keep the pest away from your plants is a better way to look after their health. In fact, you can avoid using these synthetic insecticides and fungicides in a number of instance. For example, aphids may be killed by pressing them between your fingers and thumbs instead of applying a pesticide. However, in most cases there does not seem to be any good natural alternative to save your plants.
Whenever any prudent gardener uses chemical fertilizers, he will necessarily follow the instructions on the label of the insecticides and fungicide packages or bottles. It is important that you never use these chemicals in excessive dosage, more than what is mentioned in the instructions, because increasing the amount of these synthetic insecticides or fungicides will never make them more effective. On the contrary, excessive use of these chemicals may cause more harm to the plans that the insects or diseases, which they are supposed to take care of. At the same time, it will make the environment more toxic.
When a lily bulb breaks down owing to reasons apart from pathogens, the condition is referred to as physiological bulb rot. Various things like damage caused by rodents, winter injury, complete collapse of the bulbs that are harvested much before time and several others are responsible for physiological bulb rot. When this condition affects a lily, the plant starts decaying very rapidly. Precisely speaking this condition results in the bulbs becoming wet, having a glazed appearance and making them soft as well as mushy soon. This condition does not involve any primary micro organism. However, you may soon find secondary micro organisms, especially those that survive on dead tissues, making their appearance.
This disease is attributed to fungi growing on the tissues of sprouting lily seedling and also the seedlings of other plants. It has been found that the grass-like seed leaves, which are also referred to as cotyledons, of epigeal germinators (plants whose cotyledons appear above the soil) are more vulnerable compared to the cotyledons of hypogeal germinators (plants whose cotyledons grow below the soil surface). In fact, many different fungi are responsible for the damping-off disease. The first true leaves or cotyledons just fall down and decay owing to the fungus attacking the tissues close to the line of the soil, resulting in the death of the seedlings soon.
Growers employ a variety of methods to prevent as well as keep damping-off in check. There are six vital things that need to be done to avoid this menace. These six methods are described briefly below.
Firstly, both amateur and commercial lily growers always need to make use of pasteurized soil mixes when they are growing the seedlings indoors. As the fungi responsible for the damping-off disease are found in all types of natural soil, it is important to destroy them either by heating or by using chemicals to make the soil safe for planting the seedlings. Secondly, all growers should always use only clean, uncontaminated containers or pots for growing seedlings. You can accomplish this by immersing the containers in a 10% solution of sodium hypochlorite (household bleach). Thirdly, all lily growers ought to use soil mixes that are free draining and water the seedlings very carefully during their early stage of growth.
Aside from what has been discussed above, gardeners need to allow the soil surface to become dry before they plant the young lilies. This is mainly because elevated humidity and damp soil are excellent conditions for the fungus responsible for damping-off disease to thrive as well as spread. In order to check damping-off, growers should necessarily water the seedlings very early in the day to allow the soil to dry up slightly ahead of nightfall.
Fourthly, all lily growers ought to provide the seedlings with excellent air circulation and the maximum possible sunlight. You should sow the seeds in such a time that they sprout towards the end of March or in April when the environmental conditions are most encouraging for their rapid development and growth. Fifth, all lily growers should also grow the seedlings outdoors in a clean, superior quality soil that has been well prepared. In fact, damping-off never causes much of a problem when the temperature is cool and there is sufficient light. Last, but not the least important, growers also need to use fungicides in order to check the fungi that cause damping-off. You can prepare a solution by mixing the fungicides with water and water it into the soil. Ideally, you should use Thiophanate-methyl, which is available widely and is a combination of many different fungicides.
Several vegetable as well as flower crops, such as Dutch iris, daffodils, and onions, may severely suffer from sclerotium disease, wherein certain fungi form a thick mass of hyphae that give rise to new fungal growth or structures that produce spores. Plainly speaking, this disease is caused by the fungus called Sclerotium delphinii var. rolfsii and is commonly know as the southern wilt of delphinium or crown rot of bulbous iris. This fungus leads to the production of distinctive reddish or brown resting bodies, called the sclerotia, which bear resemblance to cabbage or turnip seeds. Usually, this disease affects the bulbs of plants that grow robustly in the hot summer months. In fact, the warm atmospheric temperature helps the sclerotia to germinate and invade the tissues of the actively growing plants. The lily bulbs affected by southern wilt develop a rot, whose color may vary from chalky white to light brown. The rot is accompanied by noticeable white strands or mycelia of the fungus that invade the plants. When you notice the white, fanlike coarse patches of mycelia, you can be sure that your plant has been affected by southern wilt.
When commercial plantings are affected by southern wilt, you will notice rows of lilies exhibiting evidential brown patches. Southern wilt spreads very rapidly when the conditions are favourable for the fungus and by the time you harvest the plants, you will find that all the lily bulbs have turned into pulp. The sclerotia are present in abundance in the soil in the region of the plants withering from the disease and they can continue to survive even with no host for long periods - for as long as 10 years.
However, the good thing is that southern wilt is rarely carried by lily bulbs produced commercially. In fact, there are very few reports regarding the occurrence of this disease in gardens. Once you have detected the sclerotium, you should lift the plant and rinse all the healthy bulbs around the infected ones and get rid of the infected bulbs. Destroy the infected bulbs right away and also remove the soil in the adjoining region to a depth of 30 cm (12 inches). Several growers have used Quintozene to control this menace effectively. Prepare a solution with this fungicide and water it in the area of the affected plants in order to prevent the disease from spreading further. In fact, this process is usually undertaken when small areas of infections are detected in commercial lily plantings.
Southern wilt or the sclerotium disease has its origin in the southern regions of the United States and it may turn out to be a major problem for growers there especially when lilies have been planted in sites that were earlier used for planting other vulnerable plants like bulbous iris, delphinium or onions. Since the fungus is unable to thrive when the temperature is low, it usually does not pose a major threat to plants grown in the northern regions.
The lily crowns are sometimes invaded by a variety of species of water molds that belong to the genus Phytophthora. This occurs soon after the lily spikes emerge from the ground in spring. The growth of stems affected by these water molds is stunted and they continue to be stumps. Even the leaf bases that are attached to the lily stems are annihilated. While the leaves shrivel and fall, the remaining part of the crown lies horizontal on the ground. The stem roots gradually turn brown and the shoots begin to decay. Lilies that are affected by water molds are completely lost for the season, but may possibly recover in the following season. Stump rot usually occurs when the climatic conditions during spring are wet and cold. In such conditions, the growth rate of lilies is very sluggish and sometimes even mud can be washed into the crowns. This disease can be avoided by planting lilies on ridges in fields where they are grown commercially and on elevated beds when grown in gardens.
Virus is one of the greatest threats to lily bulbs and when the bulbs are attacked by viruses they show several different symptoms whose severity may vary more or less. Usually, when lilies are infected by viruses they may have distorted leaves, flowers, buds and stems; their leaves and stems may develop of light hued streaks; or the overall performance of the plants may decline drastically. It is interesting to note that while a virus may be responsible for sudden decline in the health of one lily, another lily species or cultivar may continue to live with the same virus without much difficulty. In the same way, while a plant already affected by one virus may seem to deal with microbe without much distress, but it will collapse completely when it is affected by another virus. Actually, no real part-time cure exists for bulbs that have been infected by viruses. Whenever you find a virus infected bulb, destroy it right away even before they are able to spread the contagion to other plants.
Two species of lilies - Lily formosanum and Lily longiflorum, are especially susceptible to viral infections, since these plants display the symptoms very quickly as well as distinctly. In fact, you can use these species to examine the existence of virus in other plants by injecting these plants with substances obtained from the plants that you suspect have already been infected.
Cucumber mosaic virus
Lilies that are infected by this virus display a number of symptoms, including distorted and highly streaked foliage color as well as brittle flowers and leaves. Cucumber mosaic virus may cause the leaves become extremely pale, while stunting the growth of the plants. Perhaps, cucumber mosaic virus is the most widespread and noticeable virus. This virus also infects several other garden plants, including delphiniums, dahlias and tulips.
Tulip breaking virus
This particular virus is responsible for the broken color, which actually thrilled tulip growers in the Netherlands several centuries back. When this virus infects lilies, it causes the foliage to become freckled, diminishes the intensity of the darker hued flowers and occasionally also breaks or alters their color.
Brown ring virus
This particular virus was found in lily "Enchantment". When plants are affected by the brown ring virus, their scales are stunted and they tend to be held very slackly. Infections caused by this virus results in the development of brownish rings and eventually the affected tissue passes away. At the same time, the growth of the plants is stunted causing them to remain dwarfed. The color of the affected plants also becomes paler.
Lily symptomless virus
As the name implies, it is a creeping disorder that is very difficult to detect. If you find that your plants have become less vigorous or are lacking the spiritedness of the other plants in the neighbourhood, you can suspect that they have been infected by lily symptomless virus. These plants are usually on the slippery slope of becoming extinct, and in case you are certain that you have found such cases in your garden, you need to destroy these affected plants immediately. However, you need to be careful and try to distinguish between plants affected by lily symptomless virus and those that may not be thriving well owing to other reasons like competition from plants in the neighbourhood, overcrowding, damages caused by slugs or rabbits or problems caused by drought conditions in your area.
If you have been growing your lilies for years together in soils that are heavily contaminated, the only way out to get rid of pathogens is to fumigate or sterilize the soil. Usually soil sterilization is undertaken to eliminate fungi, perennial weeds, nematodes and the weed seeds. This particular soil treatment is undertaken during summer when the temperature of the soil is relatively high, while the levels of moisture are comparatively low. Nevertheless, the soil needs to be moist to achieve best possible results.
You can mix the chemicals with water and sprinkle the solution on the ground. Alternatively, you can also inject the chemicals into the soil. Usually, you will need a tarp or plastic sheet to cover the soil after applying the chemicals in order to prevent their evaporation from the soil. On the other hand, nearly all soil fumigants are extremely toxic to humans as well as the plants and, hence, they need to be used with great caution. It is essential to put on chemical-proof external clothes to prevent the chemicals from coming in contact with the skin and also wear a respiratory mask so that you don't inhale the fumes exuded from the chemicals. In fact, this job needs to be done by professionals using industrial equipment. On the other hand, home or small gardeners considering undertaking these processes need to hire a contractor who is an expert in this job.
At the same time, it is important to till the soil properly before sterilizing it. You should get rid of all coarse organic materials and clods from the soil prior to undertaking the sterilization process. Having sterilized the soil, you should only plant bulbs or any other plant into it after a lapse of roughly six weeks. This time is needed to allow the chemicals to disintegrate in not dangerous compounds.
Occasionally, several lilies have an irregular growth patterns and this condition is called fasciation. Often, this condition is caused by pathogens or organisms that carry and transmit diseases. Usually, fasciation is distinguished by the stems becoming flat and copious small leaf production. The plants that are fasciated will usually stop flowering. However, in a few instances, as in the case of Oriental lilies, the plants may produce a huge number of flowers. In some cases, the stems of the affected lilies may become twisted and take the form of spirals or even split open. Most often, this condition is seen in older and larger bulbs like those of "Pink Perfection" and "Edith Cecilia". The inclination of lilies to fasciate is certainly a genetic issue and this condition is usually triggered by warm spring temperatures. However, fasciated plants are not diseased and they are capable of normal growth in the next season.
Frosts toward the end of spring can often be devastating for lilies in the northern regions. The symptoms of frost damage may be similar to those of certain diseases. The Chinese trumpets, which are among the most extensively cultivated lilies, are extremely susceptible to frosts. These are followed by the Oriental lilies. On the other hand, Asiatic lilies seem to be more equipped to endure frost to some extent.
Usually, the emerging lily shoots are damaged by frost. In case severe frosts take place towards the end of May and in June, which often occurs in the gardens located on high altitudes or in the northern regions, when several lilies may be in their bud stage, the injuries can be really serious. It is worth noting that air drainage or proper ventilation is of utmost importance to prevent damage caused by frosts. It is, therefore, advisable that you plant your lilies on slopes or in areas that are well ventilated and there is a constant flow of air. Take care to keep away from low-lying areas, which are usually frost pockets.
Ideally, you should select late emerging lilies for growing in garden where frost may occur late in the season. If you are residing in places having severe cold season, it is advisable to keep away from growing trumpet lilies.
Using sprinkler systems can be effective in avoiding damages due to frosts. In fact, watering may often cause tempering, as heat is emitted when the water droplets freeze up. In addition, a sling ice coating on plants can also shield the young and soft foliage by putting off the freezing and splitting the plant tissues. When there is a frost forecast, you can cover the plants with tarps or any other similar material like row-cover fabric. These materials possess the aptitude to provide sufficient protection, provided the freeze is not very severe.
When a frost has passed, you need to remove the most severely affected parts of the plants using a sharp knife. In addition, you should spray the affected parts right away using a fungicide in order to prevent the plants from being affected by Botrytis infection or Botrytis blight.