Common Lily Diseases
One of the most common questions or comments I get is “My Stargazer oriental lily has been not producing flowers like it used to and did not even emerge this year. What happened?”
Normally, most lily bulbs are very easy to grow and take very little care. However, there are on occasion, some instances that need investigation to figure out what, if anything, went wrong. It’s difficult to say just what happened without seeing the bulb before planting and afterwards. There can be many factors involved that created the bulb to die or not produce; planted too shallow, a virus or disease, too wet of soil…So, let’s start at the beginning and look at the more common issues.
Oriental and Orienpet lilies are probably the most temperamental to grow. (The Orienpet is cross bred between Orientals and Trumpets…hence the name Orienpet). These two outstanding lily varieties take a little extra care and thought before you plant them. However, they are well worth the extra effort. They are extremely fragrant and produce large, showy flowers and if not cared for and planted properly, they succumb to many environmental and disease problems, especially rot. I am not going to bore you with scientific explanations of each disease but will give you a summary explanation of each disease or virus and focus on control or preventative things you can do to help your bulbs thrive for years to come. Please keep in mind that like all living things, your lily bulbs will eventually succumb to age and eventually expire. Just when this happens is anyone’s guess.
The key to sustaining healthy bulbs that produce vigorous and vibrant flowers each year, is: to start with a healthy, disease free bulb; maintain healthy, disease free soil; and location, location, location! Where to plant is more important than when to plant. Things like drainage, soil texture, air circulation, light, water, food, soil and plant ph all influence the health of your plants. Gardeners who strive to understand the requirements of each particular plant they are growing eliminate those factors which affect the plants in a negative way and increase positive actions for healthier plants.
Take a little extra time in choosing your location and get to know your soil. Orienpets and Orientals do much better when placed in an area where there is morning sun and afternoon shade. Even in the shade, temperatures can reach well over 90 degrees as long as they are not exposed to direct sunlight. If they are, the leaves will scorch or burn and the flower will wilt and spend its’ beautiful appearance too soon.
The soil should be healthy and well drained. I always place a handful or so of rich potting soil or well aged compost in the hole during planting. This will revitalize the micro organisms. I will also place about a tablespoon of 10-20-20 commercial fertilizer or even rhododendron fertilizer with no more than 7% iron in the blend. Be sure not to place the Oriental or Orienpet bulb in an area you will be watering often. They only need watering when the stem has emerged and is growing to form its’ flower buds. After covering the hole, I will sprinkle a 14-14-14-7 80 % slow release fertilizer at ground level and mark each bulb placement. This is important for all bulbs because once the stem has been spent or dies, you will need to fertilize again and without knowing where the bulb is, you may be wasting the food. You should replant and repeat this process every year or so assuring the “mother bulb” stays healthy, is not placed in water saturated soil, and well nourished therefore producing its’ full bloom color and healthy stem.
Above ground feeding: Each Fall and Spring, feed your bulbs with the above mentioned fertilizers and even place a couple of handfuls of rich potting soil around the stems.
Probably the most important fact with regards to disease resistance is the overall health of your plants. Like all living things, a healthy vigorous plant is much more resistant to sickness and an organism under stress is extremely susceptible to diseases and insects (I’ll address insects in another article soon).
The most common diseases are Botrytis, powdery mildew, and stem and bulb rot. All diseases either occur as a direct result from environmental conditions or the bulbs were infected at the nursery you purchased them from. However, in most cases it’s an environmental issue. Let’s take a closer look at the causes and some corrective action…
Viruses are very simple organisms and are nothing more than RNA contained within a protein shell. They are so small and can only be see seen with the aid of an electron microscope. They invade a cell by injecting its own RNA into the cell, hijack the cells’ DNA and replace it with the Virus RNA several times. The new viruses grow in the plant cells and mature. Once mature they burst open from the infected cell and move to infect other cells, starting the process all over again. When this happens the normal plant cell functions are disrupted with symptoms showing up on the exterior of the plant surfaces in the form of streaking or molting, twisted growth, reduced plant size and or rings on the bulbs. Many species and some cultivars are more susceptible to viruses, others can tolerate them quite well with little or no symptoms.
These three most common viruses found in lilies are often transmitted by aphids that have bitten into the infected plant and ingest the virus. When they have landed on a non infected plant, they pass the virus to it after biting into it. They are: Lily Symptomless Virus or LVS (the most common), Tulip Breaking Virus or TBV, and Cucumber Mosaic Virus or CMV.
Control: Viruses are extremely (if not impossible) to control with commercial spray treatments. However, there are a few steps you can take to help prevent further infections: 1.) Dig out and destroy the entire plant preferably by burning. 2.) Disinfect your tools immediately, soaking in 100% bleach. 3.) The most important method of controlling viruses is to have good gardening practices and observe your lilies regularly. Be aware that some nutrient deficiencies can cause streaking (resembling a virus infection) in leaves and flowers. The continuing hybridization of viral resistant cultivars will also greatly help to control future problems. Check with whomever you are purchasing from for susceptibility of any lily cultivar.
Fungi are organisms that live in or on plant tissues and thrive on a host plant or in the soil on decaying leaves or wood. They are closely related to mushrooms but do not necessarily grow the fruiting bodies that are known as mush-rooms. The fungi take their nutrients from the plant and destroy the host material. The two most common and recognizable diseases that cause the most problems in lilies are Basal Rot and Botrytis blight. Basal Rot is more destructive to the entire plant because it attacks not only the stem but the bulb also. Botrytis attacks the leaves, stem, and flowers as it weakens the entire plant over time and can kill the lily.
Most fungal diseases can be corrected with commercial sprays, however there are some that cannot. If after several treatments the disease comes back, it is best to destroy the plant and start again with a new, healthy one.
Basal rot on lily bulbs is caused by two different fungi. Fusarium oxysporum va lilii and Cylindrocarpon. Fusarium has a tendency to attack Asiatics while Cylindrocarpon attacks Orientals and Orienpets. Of the two, Fusarium is the most serious and can exist in the soil for years without a host. It is easily recognized by a dark brown rot that extends into the bulb scales from the basal plate. The scales might fall apart as they become unattached from the mother bulb. The pathogen enters the plant from the roots, moves into the basal plate, and then into the scales. It reproduces by spores which can be carried in the soil by decaying wood or previously infected plant tissue, garden or agricultural tools, packing material, bulbs, and even potting soil.
Basal Rot usually shows symptoms of premature yellowing of foliage, stunting and premature drying of the stalk. Scale bulblets that form from the mother bulb are usually infected. Basal rot will usually destroy the mother bulb and any bulblets that have formed from the basal plate are infected. However, in efforts to survive, the plant may grow large numbers of stem bulblets (located just below ground level and on the main stem) which normally are not infected. So, these can be dug up and planted in another location to continue the cultivar. Do not replant anything, if possible, in the same spot as the infected lily for four years until the spores die. Clean your garden tools and equipment before you plant the new bulblets.
Control: Some final thoughts on basal rot: Once this disease infects a plant, it cannot be corrected or controlled and is useless to try and save it. ALL of the infected plant must be removed and destroyed. However, there are some preventative sprays that can be applied before it becomes infected. Consult with your local extension office or garden center. Plant only healthy, non-infected lily bulbs and completely get rid of ANY bulbs, scales, and bulblets that show signs of the disease. Stem bublets can be saved.
Fusarium is most active in places where soil temperature and moisture level is high. Usually in the North regions (Zone 3, 4, and parts of 5) where soil temps are lower, it’s not a problem. Unless you are growing your lily bulbs in a container outside then moving them indoors during the colder periods.
1.) Avoid fertilizers high in Nitrogen. High Nitrates will cause rapid soft growth of the bulb. Organic fertilizers such as manures and composts must be aged (two to three years) and used ONLY as a top dressing or placed no more than an inch below the surface. Well rotted manures and compost will keep the soil cool and help control Fusarium, which needs warm moist soils to propagate.
2.) Control soil moisture. This is especially true when planting your bulbs in commercial potting mix in containers. In most cases, commercial potting mix contains a wetting agent which keeps the mix moist, even in dry conditions. Lilies do not require a lot of moisture to thrive. Avoid overwatering during the months of hot temperatures. When planting in a landscape area, make sure the soil is well drained and light in texture. Light, well drained soils are better than heavy soils thus reducing the moisture that Fusarium needs to survive. This will not affect the bulbs too much because they store moisture in the scales.
3.) Fusarium likes acidic soils and adding some lime at the time of planting and each year along with fertilizing, will increase the pH to a more neutral or alkaline level is advisable in some soils.
4.) Avoid damaging the bulbs during planting, transplanting, and weeding. Any lesions (this includes scales that have been removed) will be an entrance for the fungi.
5.) If possible, try to purchase resistant varieties as chemical control is becoming limited for various reasons.
Botrytis is caused by two species of fungi (B.elliptica and B.cinerea) which attack the above ground plant parts. B.elliptica is the more destructive of the two and both fungi can be found on the same plant at the same time. B.cinerea attacks the leaves, open flowers, and seed pods in cool summer weather and late fall. The warm, moist coastal regions of the Pacific Northwest or western coast regions of Britain are often called “Botrytis Climates”. Dry, cooler climates are rarely affected.
The fungus will over winter on the leaves of the previous year and produce spores in the summer months that are spread by wind or splashing water. The first sign of Botrytis are white spots on the leaves then becoming teardrop shaped on the upper surface. They are lighter in color on the margins and darker in the center. As the attack continues, the leaf collapses and decays and the fungus produces more spores on the decaying leaf.
Control: Botrytis only attacks the surface of the plant and will spread to other surfaces or neighboring plants as more spores develop. Moisture is essential to the spread of this fungi, therefore careful watering practices should be followed. It is better to use soaker hoses or drip line method rather than over the head or top sprinkler type watering. Good air circulation is also important for this disease as well as others in order to dry the leaves as soon as possible after watering or rain occurs. Try not get the leaves or the flowers wet. Look for infected leaves and remove them asap while they are still wet. This will stop or prohibit the spread of the fungi. Warm, dry sunny weather aids in controlling the fungi.
There are commercial fungicides that can prevent and control this disease. Again, consult with your local garden center or extension office.
Root rot is not a disease but is directly associated with poor drainage. If a bulb or any other plant is placed where there is little or no drainage for water, then it continuously sits in water and the roots along with the bulb eventually rots. Lack of good soil aeration, planting in thick heavy fine textured soils like clay, is detrimental to lily bulbs. To prevent this from occurring, plant in light airy soils that drain water quickly so the roots and bulb do not sit in water for long periods of time. Roots need oxygen and being in water provides little or no oxygen.
Photos Courtsey of: Some Technical References: