It’s true—lilies have been difficult plants to grow in the average garden. But now, thanks to 20 years of research on lily diseases, growing lilies can be a very gratifying gardening experience.
Success With Lilies
Success with lilies requires that the grower of bulbs and the gardener fully use the present knowledge of lily diseases.
The control measures for these diseases are not difficult but require some study and long-range planning.
Getting out the sprayer about June 1 and squirting some all-purpose mixture on the plants at intervals is not the answer.
Control Of Lily Disease
The control of lily diseases should be approached as a challenge to the skill and knowledge of the gardener.
There are many interesting angles, and the reward for mastering the subject can be a large and varied assortment of plants as beautiful as any that can be grown in the garden.
Three diseases of lilies are important:
- Mosaic, a virus disease
- Botrytis, a fungus disease of the foliage
- Basal rot, which attacks the bulb
Other diseases are usually of minor importance.
Mosaic Disease
Mosaic is the most important disease of lilies. It is the principal reason why lilies have been considered difficult to grow.
The virus is systemic, that is, it is found in all parts of the plant except the seeds. It does not live in the soil or dead parts of the lily plant.
The virus is commonly transmitted from infected to healthy plants by aphids, the common melon aphid being particularly offensive in this respect.
Any environmental condition that favors the aphid and its movements means an increased rate of spread of mosaic among the lilies.
Lily Mosaic Causes
Lily mosaic causes the leaves to become mottled with irregular, elongated light streaks, varying in width and sometimes extending the entire length of the leaf.
The symptoms are very distinct in L. auratum, speciosum, superbum, canadense, monadelphum, formosanum, and others, especially in early spring when the leaves have expanded and the weather is still cool.
Unfortunately, with some species, the symptoms are less distinct, especially after a few warm days. And even the expert would have trouble identifying mosaics in virus-tolerant species.
However, it is best to be suspicious of lilies in which the leaves are not uniformly dark green. Chlorosis, probably caused by iron deficiency, produces a yellowish coloring, but the pattern is uniform, the areas between the leaves turning yellow while the veins remain green.
How To Control Mosaic Disease
The control of mosaic may be handled in various ways, depending upon how deeply involved you are in lily growing.
The collector of every new lily on the market has a different and much more difficult problem than the gardener who grows only a few species.
Lily mosaic is not transmitted through the seeds; hence all lilies raised from seeds, away from diseased lilies, are healthy.
The best advice I can give the beginner with lilies is to raise all of his lilies from seeds and have no others in the garden or within a few hundred feet.
However, since many will purchase bulbs, it will be necessary to resort to roguing out and destroying the diseased lilies as soon as the symptoms become evident in the spring. The diseased plants should be removed from the garden and burned or buried, not left to wilt near healthy lilies.
Another approach to the problem is based on the fact that some lilies rarely become infected with mosaics, while others, even though infected, are very tolerant of the virus and may be expected to perform well.
There are enough of these to make a fair showing in the garden without growing the susceptible types.
Virus Tolerant Lilies
The Martagons, L. hansonii, and hybrids between them, including the Back-house hybrids, rarely take mosaics. L. pardalinum and the Bellingham hybrids are fairly free from the mosaic.
Virus-tolerant lilies include the umbellatum group, the elegans varieties, the trumpet lilies, and their hybrids with Henryi, of which Havemeyer and aurelianensis and their numerous offspring are being widely distributed.
Others are L. candidum, testaceum, speciosum, tigrinum, and its horrible double variety, the Croft and Estate varieties of the Easter lily, and probably some of the more recent hybrids of L. tigrinum and L. willmottiae.
Breeders of these lilies are undoubtedly developing virus-tolerant lilies, either consciously or unconsciously.
I am not prepared to say whether this is good or bad, but those who have these in their garden will not be able to keep the lilies that become infected readily and deteriorate quickly.
Among the susceptible types are the following:
- L. auratum
- Browni
- Colchester
- Canadense
- Cernuum
- Formosanum
- Japonicum
- Leichtlinii maximowiczii
- Monadelphum
- Rubellum
- Sargentiae
- Other less common lilies
These must be grown apart in front of the others and must be rogued carefully.
Botrytis or Botrytis Blight
Botrytis blight, or botrytis, is a fungus disease that attacks foliage. L. candidum and L. testaceum are both very susceptible and in periods of warm wet weather in May and June, most of the leaves on these species may be blighted.
Occasionally even the flower buds are attacked. Other susceptible species are L. longiflorum, the Easter lily, L. sargentiae, Humboldt, washingtonianum, and form-sunlit under severe conditions, other lilies may be attacked.
The disease first appears as small reddish-brown circular spots on the leaves, which in severe attacks in wet weather may merge and destroy the whole leaf.
Prolonged wet periods, which cause moisture to remain Jong on the foliage when temperatures are 60° degrees Fahrenheit or above, favor the rapid development of botrytis.
How To Prevent Botrytis
Botrytis may be prevented, or at least greatly reduced, by spraying the lilies with Bordeaux mixture, 4-2-50, at intervals of ten days to two weeks during the period of rapid growth in May and Rine.
In wet seasons, more frequent spraying is necessary than in dry seasons. The spray should be on the foliage before, not after the rain.
Bordeaux mixture is made in three-gallon lots by dissolving four ounces of copper sulfate in part of the water, two ounces of hydrated lime in the rest of the water, and pouring the two solutions together.
The spray should be used immediately as it soon loses its efficiency. A spreader sticker, such as Penetrol, increases the effectiveness of the spray.
Copper lime dust may also be used, but the spray is more effective. If the dust is used, it should be applied when the foliage is wet with dew.
Good Air Circulation
Good air circulation, as on a slope or an airy site, favors rapid drying of the foliage after rain or heavy dews and tends to reduce injury to front botrytis.
Spraying Madonna Lilies
Many gardeners never spray their Madonna lilies and have fair results. But generally speaking, any plant on which the foliage is maintained at full efficiency throughout the growing season will turn in a better performance next year than one which loses its leaves or has its efficiency reduced prematurely by disease.
Basal Rot is a Fungal Disease of The Bulbs
The fungus, a species of fusarium, lives in the soil and invades the plant through the roots and the basal plate, causing the bulb to fall apart and the plant to die.
Above ground, symptoms are a premature yellowing of the foliage and stunting of the plant.
When these symptoms appear, the plant should be dug, and the bulb examined. Infected bulbs should be destroyed if they are of easily replaced varieties.
Rare and expensive lilies may be cleaned up and replanted elsewhere if the basal plate is still intact and only a few scales have become loosened.
Use Formaldehyde
The diseased tissue should be removed and the bulb dipped in a solution made of two ounces of Tersan in one gallon of water. The bulb should be replanted elsewhere in the ground that has not previously grown lilies.
A formaldehyde dip of one part of formaldehyde to 50 parts of water for 20 minutes has also been used but it is considered less satisfactory than Tersan.
Susceptibility To Basal Rot
Lilies vary greatly in their susceptibility to basal rot. L. candidum and L. testaceum are very susceptible. However, in some gardens, those species thrive if left alone.
It is when they are moved about in a general collection of lilies that much trouble from basal rot may be expected.
Other susceptible lilies are the Martagons and some of their hybrids, L. browni, formosanum, japonicum, rubellum, bulbiferum, bulbiferum croceum, auratum, and a few others.
The Lily Specialist
The lily specialist grows many species, brings in bulbs from many sources, and is digging, propagating, and moving them about may expect the fungus to build up in his soil to the point where it will be difficult to grow the susceptible types.
Planting sterilized bulbs in soil that has not previously grown lilies will keep the situation in hand as long as new land is available.
When all the land is contaminated with the fungus, the soil must be sterilized to prevent heavy losses.
Fusarium Species
Fusarium species are tough customers, and tough fumigants are required to deal with them. Chloropicrin or tear gas, sold commercially as Larvicide, is the most effective sterilizing agent for fusarium-infected soils. I have used it to sterilize a bed where L. testaceum died out with basal rot.
The bed was replanted with sterilized bulbs of lilies susceptible to basal rot. The performance of all the plants in this bed has been excellent, and none are known to have been infected with basal rot.
Larvicide is very unpleasant to use without proper equipment, but with a gas mask and an applicator, little difficulty should be experienced.
Basal Rot
Basal rot is sometimes serious in seed flats. Therefore, seedlings of all susceptible species should be grown in a sterile medium.
Sterilized soil and vermiculite are all satisfactory, as recommended by the Bureau of Plant Industry workers at Beltsville, Maryland, and sphagnum. Sawdust is another possibility.
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