The enemies of the lily

Pests

Voles

Voles seem to consider all bulbous plants a delicacy, and invariably attack them. It is difficult to eliminate voles completely, as they usually invade gardens from neighbouring fields, but their numbers can be effectively reduced with poisoned bait, gas, or traps.

A paste of red lead painted onto the outer surface of the bulbs also affords some protection, as does wire netting placed round the bulbs and buried in the soil; some nurserymen sell specially-made wire baskets for this purpose.

Field-mice

Damage is likely to take place during the winter months, and usually only when bulbs are covered with the thick layers of straw or leaves in which mice like to overwinter. Any one of the good and numerous proprietary poison baits will control them effectively.

Slugs and snails

Unless slugs and snails are kept in check, they can cause considerable damage to young, growing shoots. The leading shoot is usually the first to suffer, but seedlings, even if kept in a coldframe, are often attacked. Bulbs, too, suffer from slugs, which during the autumn and winter months retreat into the soil. Fortunately, both slugs and snails are easily controlled if one of the various slug baits produced from a base of metaldehyde is scattered on the lily beds. Bait application should commence as soon as the weather turns warmer during early spring, and be repeated frequently throughout the growing season.

These microscopic worms penetrate the roots, leaves, and buds of plants from the outside. Nematode development is dependent on soil moisture and rather high temperatures. The amateur has little to worry about, and will hardly know of the existence of nematodes, but they can be a serious nuisance to the commercial producer, who may suffer great and severe losses, particularly as nematodes multiply rapidly wherever monoculture without rotation is practised.

As far as lilies are concerned, only two types of nematode need receive attention: leaf and flower nematodes, and root nematodes.

Leaf and flower nematodes enter the leaf through the stomata, but require damp weather to enable them to do so. Leaves and flowers become discoloured, lifeless, malformed and eventually turn brown. To combat leaf nematodes (mainly of the type Aphelenchoidcs fragariae and A. ritzemabosi) the bulbs are immersed in a formalin solution (one part 45 per cent formalin plus 200 parts of water) for 60 minutes, and must be held at exactly 111 DEG F (44 deg C). It is vital that both temperature and timing should be exact if the treatment is to be successful. Bulbs are subsequently dipped in a fungicide solution and air-dried, and should be planted within three days of treatment. Protection must be maintained to control those nematodes which may have wandered to the extremities of the plant – either the stem or the leaves – by spraying plants three times during the growing period (allowing four to five days between each application) with a systemic insecticide, Metasystox or Nemafos.

Root nematodes, the free-living Pratylenchus penetrans and P. pratensis, are chiefly concerned with lilies, and are not to be confused with nematodes causing gall formation on roots. They are more difficult to control than the leaf and flower nematodes, and live in the soil, from where they enter the lily bulb. Attacks are recognized by yellowing and dying of leaves and severe destruction of roots until only a few stumps are left. In the larger lily beds attacks are usually confined to a few isolated patches.

Care must be taken only to plant nematodc-frce bulbs in nematodc-free soil. If attacks do take place, the damaged roots of affected bulbs should be cut back to healthy tissue which automatically removes some of the pests. Infested ground has to be treated by chemical means, and proprietary products such as Basamid, Shell-DD, Di-Trapex (WN 12), Larvacidc, Tcrabol, Trapex, and Vapam are all useful. According to manufacturers’ instructions, the chemical should always be applied to freshly forked ground, which is then scaled either with polythene foil or by flooding. Root nematodes are often the cause of secondary infection, namely fungi. Dutch findings indicate that certain plants are nematodc-resistant; Tagetcs is an enemy of free-living nematodes.

Millipedes

Recent us observations have dispelled the once prevalent idea that millipedes do not damage lily bulbs; on the contrary, they cat the bulb scales and cause considerable damage. Aldrin or Gamma pellets provide effective control if scattered over the soil surface and also if buried in the ground; systemic insecticides applied in water solution are equally effective.

Lily beetle (Crioceris lilii Scop.)

This pest (22) only attacks lilies and Lily of the Valley. It is ½ inch long, sealingwax-red, and lays red eggs, neatly arranged in rows, on the underside of lily leaves during May and June. The yellow larvae soon emerge and continue the damage by feeding on leaves, buds and flowers. Lily beetle damage is characterized by a scries of semicircular notches on the leaf margins. These pests are fortunately confined to certain locations, but if present they unerringly find their way to the nearest available lily. Remedies are numerous: physical removal of beetles and larvae from the plant, dusting with parathion, repeated spraying with DDT or Mcta-systox. Plants need to be watched carefully during the autumn for a second generation of beetles.

A close relation, which attacks lilies and onions, is Crioceris meraigera L.

Lily thrips (Liothrips vaiicccki Priesner)

Lily thrips are small insects, – ½ inch long at the most, and shaped like a comma; they are either black, brown, or milk-white according to their stage of development.

Thrips live in the spaces between lily scales on which they feed, severe attacks causing flower malformation. Thrips mainly damage and puncture the outer skin of the bulb scale, which in turn make it prone to fungal attack. Lilies with a loosely formed bulb system, like the Asiatic varieties and also hybrids, are more likely to be attacked than the firmer-bulbed trumpet lilies. Thrips-damaged bulbs can always be easily detected by their most disagreeable smell! Thrips attacks are fairly widespread in the United States, both among wild and cultivated species, also in Japan and Europe. The Dutch method of repelling these attacks is to immerse the bulbs for 15 minutes in a solution of 4 cubic inches parathion (25 per cent) to 2-½ gallons (2- ½ – u s gallons) of water, followed by a cold-water rinse. The ground must also be treated with pound of aldrin to every 80 square feet. The Americans advise hot-water treatment, whereby the bulbs are kept in water at 110 DEG F (43.5 DEG C) for one hour. It is important that the water should remain at this exact temperature throughout the period of treatment. The spraying of growing plants with a systemic insecticide, parathion or Metasystox, is beneficial. Dusting the bulbs when they are planted with DDT is also deadly for thrips.

Aphides

In addition to damaging steins, leaves and flowers, aphides are also responsible for the spread of virus diseases; particularly dangerous in this connection are the green peach aphis (Myzus persicae) and the potato aphis (Macrosiphum solanifolii). The winged forms fly from plant to plant, puncture the surface to feed, and so transmit virus diseases, if present, from one plant to another.

Three-to-four-weekly spraying with a systemic insecticide, such as Metasystox, is recommended. All plants susceptible to aphides, e.g. roses, in the vicinity of lilies, as well as the lilies themselves, should be sprayed to avoid rapid reinfestation. Systemic insecticides are absorbed by the plant and remain in their sap stream for up to three weeks; spraying, therefore, not only kills the aphides on the plant at the time but also all those which try and feed on the plant up to three weeks after spraying.

Fungus diseases

Botrytis and fusarium are the most prevalent fungus diseases, and they can both cause severe damage, us growers also have to cope with a number of other fungal diseases, but these two are the main ones.

Botrytis

This fairly common and widespread fungus (23) damages leaves, blooms and stems. It is most prevalent in summer during humid and warm periods when sunshine and rain, mostly as a result of thunderstorms, alternate. The first signs, usually on the leaves, appear in the form of small round or elliptical-shaped brown areas (Botrytis elliptica), but during the later stages a second fungus (B. cinerea) attacks leaves, stem, flowers and seed capsules. Clusters of spores cover the whole plant with a greyish mould.

Botrytis develops quickly among wet petals, which after blooming and during storms drop onto the ground and from there reinfect hitherto healthy plants. Leaves and stems die off in turn. Although botrytis does not directly attack the bulb, it retards or even stops its development, as leaves are no longer able to assimilate nutrients, and are therefore unable to nourish the bulb. Seed capsules are of course also affected, and seeds loose their viability.

Spraying every two weeks from the end of May onwards with either captan (orthocide) or thiram (TMTD) (Pomarsol) is useful. The Americans, including Jan de GraafF, find that Bordeaux mixture is difficult to improve upon as a control material. It is made as follows:

To obtain 2 gallons (2-½ us gallons) of spray material, I ounces of slaked lime is stirred into 1 gallon (\ us gallon) of water contained in a plastic bucket (a metal bucket is liable to be holed by the mixture). Similarly, and again using a nonmetal container, I ounces copper sulphate are dissolved in 1 gallon (1£ us gallon) of water. The copper sulphate solution is then poured into the well-stirred lime solution (never the other way round). Finally a spreading agent or f cubic inch of Alginurc is added.

The spraying of lilies against botrytis should take place every 14 days, particularly where lily plantings are fairly dense, for under such circumstances plants remain damp for longer periods, and provide ideal conditions for botrytis to spread.

Fusarium

Probably more lilies – up to 80 per cent – are lost from this fungoid disease than from any other cause. Practically all Auratum bulbs imported from Japan die after a year or two from this very trouble.

Bulb scales and bulb basal plates are attacked, and show signs of brown or black-coloured injuries which spread outwards to the roots and cause them to die off. Further progress of the disease breaks up the bulb scales until often only their tips remain. The fungus Fusarium oxysporum f. lilii is the cause, although other fungi and bacteria are also partially responsible for this destruction. It is found in most soils, and builds up rapidly if lilies continue to be grown on the same ground.

To avoid infection, beds should be chemically treated before lilies are planted out. Formalin, Vapam, Trapex, and Larvacide, in addition to other proprietary chemicals, are used. Always follow the manufacturers’ instructions exactly, as many of these chemicals are poisonous and corrosive.

Good results are being obtained in the United States from bulbs disinfected with either Tcrraclor, Captan or TMTD. Healthy bulbs are immersed, for 10 minutes, in a solution consisting of ounce Terraclor plus •} ounce Pomarsol (TMTD) or Orthocidc 50 (Captan) in 1 gallon (1- ½ us gallons) of water. They are then lightly dried and planted immediately. Brassicol may also be useful for disinfecting soils prior to lily-planting – one spoonful per bucketful of soil.

Virus diseases

Almost all plants are prone to virus attack of varying degrees of severity. Lilies are no exception, and the almost complete destruction of L. longiflomtn in Bermuda during 1919-25 led to a detailed investigation of the problem.

It is impossible to give a detailed account of all the virus diseases which occur in lilies – in any case, they are not only confined to these plants. It is only during the last few decades that significant scientific progress has been made, and not all the facts are yet known.

After the L. lougiflorum disaster in Bermuda, F. P. McWhorter and Philip Brierley investigated the virus disease complex and fully reported their findings in the North American Lily Society Year books of 1955 and 1963.

Viruses react differently on different lilies. Some lilies are completely destroyed, others are hardly harmed and barely show visible effects. Some viruses are described as symptomless, and plants only show effects after they have received a second virus infection. Vectors are mostly aphides and, according to latest scientific evidence, also thrips.

The rosette virus only affects L. longifionim and is transmitted by the melon aphis. The leaves distort and curl, in roscttc-likc manner, and plants invariably die.

The fleck virus is easily recognized by the formation of fine, long, light or white streaks along the leaves. Longiflorum fleck arises as a result of the combined attacks of Cucumber mosaic virus and the symptomless virus – but again only in L. longiflorum.

Spcciosum fleck only attacks L. speciosum var. nibrum and also maize. The pest responsible for transmitting the virus is the green peach aphis.

Longiflorum streak originates as a result of Echinocystis-Mosaic virus, found on Echinocystis oreganus, of cucumbers and watermelons. It apparently affects only L. longiflorum, and then only in north-western parts of the United States. The vector seems to be the 12-spot cucumber beetle.

Mosaic virus disease is clearly recognized by the mosaic pattern changing the leaf colour from dark to light green. Young, not yet fully unfolded leaves also show the change of colour pattern quite distinctly in the form of spots or lines.

Tulips are apt to suffer from the same disease and show similar symptoms. In fact all striped tulips suffer from mosaic virus. They are differentiated as follows: 1. Colour-adding virus. Tulip colours gain in intensity, lily leaves bear the typical mosaic patterned lines 2. Henryi – mottle virus. Mottles the flower of tulips, causes mosaic in L. henryi and one or two other lilies; apt to destroy L. regale 3. Mild lily colour-removing virus. Produces contrasting colour patterns in tulips; causes the typical mosaic pattern in several lilies, including L. auratum, L. speciosum, L. tigrinum, and L. x umbellatum; blooms of L. speciosum and L. x mnhellatum become flecked 4. Severe lily colour-removing virus. Changes the colour of tulips to white and kills them; often present without symptoms in L. longiflorum, L. candidum, and L. tigrinum 5. Lily vein-darkening virus. Changes the colour of veins in tulip blooms; present in healthy lilies, particularly in the Ace varieties of L. longiflorum

The nonprofessional finds it difficult to distinguish between the different symptoms, but the disease is easily recognized on close examination of the young shoots. If they are carefully unrolled they reveal a light and dark-green mottled pattern if the disease is present.

The observance of the following points aids the prevention and reduction of the incidence of virus diseases: 1. Virus-1nfected plants, including the bulb, must be dug up and burned 2. Aphides transmit virus, and lilies have to be protected from them. Preventive spraying at minimum four-weekly intervals is advisable, preferably with a systemic insecticide (e.g., Metasystox) 3. Particularly susceptible lilies (L. forittosanum, L. auratum, L. spedosum, L. tigrinum) should be planted on their own, as far away as possible from other lilies 4. Lilies should not be planted in the vicinity of virus-carrying tulips 5. Lilies should be grown from seed. Seed, even if obtained from a virus-1nfected plant, cannot transmit virus

Not all virus-1nfected plants succumb. There are lilies which continually carry a symptomless virus and are perfectly healthy – e.g., L. tigrinum, L. longiflorum Ace, and L. candidum. But virus-1nfected plants present a great danger, as vectors can so easily transfer the virus to a healthy plant. Virus infections progress gradually, and debilitate plants over a period; first the shoots and flowers become malformed, later their vigour decreases, until the plant eventually dies. During the later stages, the weakening plant is also often attacked by fusarium or botrytis, which hasten its end. So far, no effective means of curing virus-1nfected lilies has been discovered.

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