Pests and Diseases and Other Things that can effect the Longevity of lilies in Cultivation

We are listing some chemicals. Some may either not be available for amateur use or may not have official approval for such a use in this country It is difficult to know what is still available as some are withdrawn for no sensible reason. Where possible other methods of control are usually preferable, but often chemicals may be the only resort. It is generally best to use pesticides which have low toxicity to non target species and are biodegradeable in the environment. Pesticides usually work better when applied to the plant and close surround not the general area. When using chemicals always treat them with respect and keep them safe when not in use

Biological control methods are generally preferable. At present I do not know of any single natural predator which will give complete control of any pest in lilies, but they may be useful in keeping problems down. Only native species should be used in biological control. In the authors opinion biological control methods are preferable to chemical methods - providing of course they work! Biological control methods can be bought in the bottle, but their are quite a number of natural predators that come for free They may need a little bit of encouragement to build up numbers.

Introduction

Lilies do not suffer from as many problems as some other plants. However some problems are serious but most of these problems can be quite local. Some problems have not yet made it across the channel-though though with open borders they will soon be forced upon us.

Some of the pests and diseases which effect lilies are specific to lilies and although they can do serious damage to lilies they have to find their host plant first. Lilies are extremely rare in the wild in this Country and are usually only found in gardens. These pests rely on Man to help spread them. Sometimes a problem can lead to secondary problems such as virus attack can make a plant more susceptible to Botrytis. Slug damage can open the plant up to invasion by fungi.

The authors preferences for control of pests and diseases are in order. Physical control, Biological control and finally Chemical control.

Physical controls are essentially actions which can prevent problems in the first place, such as growing plants in separate groups, on clean ground and under favourable conditions. Even when a problem does breach this defence the rate of spread is likely to be a lot slower

Biological controls This covers selection of plant material for resistance to particular problems and bio-control - the use of natural predators to check the problem. The author has unfortunately had little success so far with introducing particular predators but more success in encouraging existing predators. There is no doubt that their will be some much needed major advances in this sector over the next few years

Chemical controls generally as last resort the answer comes out of a bottle. It may be a necessity, if so the choice of chemical should be one which has minimum effect on the environment and preferably one which only effects target species.

The following problems are listed in order of frequency, the most common first

Problems which can occur frequently and are widespread

Man. (Homo sapiens (sub specie) destructor (!)) a degenerate member of primate group of mammals. Occurrence very common. Typical symptoms of damage are generally the non appearance of the shoots, if the bulbs are dug the stem is severed or the bulb is damaged. If the bulb is not destroyed immediately it frequently opens the plant to secondary infections. Typical symptoms of the presence of this problem are disturbed soils, often broken down to a “tilth”. Man is by far and away the worst pest of lilies in the UK. Lilies in the wild have grown without mans help for millions of years. They often have a short life at mans hands. They are often planted and hanledincorrectly (see cultivation). Mans destructive nature extends to stabbing, spearing, chopping and trampling the bulbs and young shoots. This behaviour is generally worse in Spring when a sort madness inflicts some individuals marked by an over enthusiastic fever (sometimes known as “Spring Fever”). Slugs generally get the blame for a lot of this damage. Man is also the major spreader of most pests and diseases. Lily beetle for example was introduced by man to this Country and its continued spread to new areas within the UK is almost always due to being constantly reintroduced. Although this is generally due to ignorance, there is no doubt (!) that in a few cases it may be deliberate. One can hardly imagine quite why some people do this.  Control Baiting, Trapping and shooting, however satisfying, are unfortunately are not an option. Eradication of this problem has to be that of control and education. Locking up hoes and spades can work wonders. see cultivation for control methods

Lily Disease.                                                                                                                                               (Botrytis elliptica) (grey mould) Symptoms Leaves typically show elliptical shaped spots. The tips of the leaves are often infected. Lower leaves become shrivelled especially on second year infection. Infection can get into the stem and the whole plant collapses. In damp conditions a grey mould can be observed over the surface of the effected part of the leaf. The disease is not known to normally attack the bulb perhaps partly because the bulb is generally planted deeply. Occurrence is common. Control Lily Disease or Botrytis Elliptica is a wet weather disease. The spores are dispersed in the wind, when they settle they will germinate in droplets or a film of water and given time try to penetrate the leaf. Keeping the plant as dry as long as possible reduces the risk of infection, IE a sunny well ventilated spot. Botrytis elliptica is supposed to be different to the grey mould that effects most other plants (Botrytis cinerea) and is specific to Lilies. Although Botrytis elliptica is quite widespread because the spores can spread considerable distances, as distance increases the number of spores are reduced and therefore the chance of attack. Even short distances between plants will make a difference. When planting lilies in the garden planting in small groups with other plants between reduce the chance of spread. If you have only a few lilies infected, hand picking leaves is very effective. Plants can also be sprayed with fungicides generally fungicides effective against ordinary botrytis. Fungicides which can give control include (if still legal to use in the Country) Captan, Thiram, Zineb, Mancozeb, copper fungicides such as Bordeaux Mixture, Liquid copper. Elvaron has been used outdoors but can cause scorch under cover. Benlate normally no longer give control of this disease.                                                                                                                                                         The normal spores of Botrytis are relatively short lived and have to find a host lily within a few days before they die however this disease produces over wintering spores which sit on the surface of the soil waiting for the plant to grow again. If you have had problems the previous year it would be a good idea to skim the surface of the soil and remove and put on a fresh mulch. The over wintering spores can only survive till the Spring and cannot effect other plants so moving the effected soil just a few feet can prevent reinfection.                                                                                 Lily disease is not a disease that happens in every garden and every year, it can be quite serious if unchecked. Much can be done to prevent its spread by cultivation techniques, but if necessary fungicides can give good control. It is probably a good thing to have a zero tolerance of this disease as once eradicated it may not reappear for years. Some early work has been done on biological control, the author has had no experience of this.                                       For information it has been recorded that Botrytis needs ultraviolet radiation for germination of Botrytis spores, therefore in theory when grown under cover a ultraviolet screen should prevent the spread of this disease without spraying. The author has also made some observations. When growing large numbers of lilies where botrytis was present in the open infections have largely “dried up” on their own following hot dry and particularly sunny periods. Whereas it is understandable that new infections would decrease a large amount of “ghost spotting” has been observed at the same time. “Ghost spotting” is where new infections have actually died out on their own. The author is convinced that high ultraviolet levels will also kill Botrytis elliptica (!).

Virus Diseases   section not complete

Slugs and Snails                                                                                                                                               (several species) There is no doubt Slugs and Snails can do a considerable amount of damage to Lilies. Most damage is generally done to the emerging shoot and colonisation of the bulb. In the UK Slugs tend to be more widespread than Snails. Symptoms Slugs tend only to attack the above ground parts earlier in the year before they get tough. They will also attack bulbs all year round if they can find them. Wandering Snails will occasionally attack lilies quite high up in the plant and later in the year. Slugs and snails have a “rasping” tongue ie they eat their food by scraping pieces off the plant. This means that will drill holes into bulbs and shoots and can eat leaves. Because of their method of eating they usually leave a curved surface and generally tends to leave the upper epidermis (skin layer) of the leaf or the outer epidermis of the scales projecting slightly. Damage is not usually fatal to the lily unless very serious, but can be an entry point for other pests and disease. Control There are slugs and snails which are actually beneficial to your plant - some of these eat their fellow molluscs. Their are snails that specialises in eating algae growing on the leaf surface. Their are two main types of slugs which do damage - ones which frequently live and feed on the surface - and ones which largely live and feed underground (“Keeled” slugs”). Keeled slugs can be more difficult to control and can be extremely destructive, and yet are not often seen until the damage is done. Keeled Slugs although widespread within the country they are often extremely localised in the garden. They rarely come to the surface but swim through the soil. This may look a great option for them, however soil is not an inactive lump of minerals it is a complex living organism. They have to swim through this and although they may find food there are things there which would just love to put a slug on its menu. Hence colonies of keel slugs tend to be localised. With slugs and snails biological or an integrated pest control is more practical. Baits or drenches can be quite effective in reducing the damage. They are normally based on metaldehyde, methiocarb or Aluminium Sulphate. Paris Green used to be quite effective. Baits are generally mixed with bran as a base to attract the prey and are best applied in warm damp weather. Metaldehyde and Aluminium Sulphate are sometimes used in liquid form as a drench. Because of its action methiocarb based pellets mixed into the soil will give some control of keel slugs. All baits can be extremely dangerous to some wild life. Most baits are now coloured blue to make them unattractive to birds. Unfortunately hedgehogs are believed to be colour-blind, and certain individual dogs (IE particularly labradors/golden retrievers) have an occasional individual fetish for picking them up. Some slug baits also have a chemical smell added to discourage more animals. Aluminium Sulphate is claimed to be safe (when used as directed!) and I believe has organic approval. Paris Green is probably illegal in most countries because of its toxicity to warm blooded animals. Using baits might be the only quick option in some gardens. Most baits will also have some effect on natural predators which may also take the bait, so using baits may also make you more dependant on them in the future. A number of other methods are often used. Slug traps- do work but they often take more natural predators than slugs. Hand picking - especially on warm nights with a torch does work but what do you do with the Slugs?. Salt poured over individuals does work and is very satisfying for the slightly repressed sadomasochists amongst us, but it takes a lot of time or salt to have much effect. Physical barriers have some effect but are not sure fire. Slugs do not like crawling over rough objects. Mulching around lilies can help produce a slug barrier. Cocoa Shells and Bark are useful in Spring. In the autumn kicking some soil down the hole left by the dying lily stem will help prevent slugs finding the bulb, A methiocarb based slug pellet or two could be put down before the hole is covered in case one has already got down there.  Biological Control Is probably the most attractive and can be the most effective for some. We have been using mainly biological control of slugs for about 20 years. We have used introduced nematodes in the field to control slugs but for us they have not been very effective. In the garden as in our fields there are a large number of natural predators which can feed on Slugs, including Badgers, Foxes, Hedgehogs, Birds, Ground Beetles, Centipedes, Predator Snails, Mites and Nematodes (eelworms). Badgers foxes and hedgehogs tend to eat just a few slugs here and there, some birds however (thrush family) can have a significant effect on Snails. On the whole most individual predators tend only to crop them rather than reduces their number significantly in any one area. We found that although nematodes can dramatically reduce the number of slugs in any one area for a short time it was expensive to apply and on its own the effect was short lived. For us the most effective predator of Slugs have been the group of species collectively known as ground beetles. They are very widespread and are in most gardens. During the day they hide under stones etc. or in the soil and come out and forage at night. They will eat almost anything in front of them Slugs, leatherjackets, slug bait, beer and are one of the very few native predators which will take on the New Zealand Flatworm in fact they will take on anything! Ground Beetles are very partial to Slug eggs. Perhaps the biggest point of slug control is the destruction of these eggs by the beetle though they do take on any sized Slug. Ground Beetles are black and scuttle around quite fast when disturbed. They are the medium sized beetle that is often seen scuttling around on the carpet particularly in the autumn. The juvenile beetle is also black and quick moving a rather sinister looking sometimes quite large and long flexible black insect. These insects are worth their weight in gold to the gardener and do not deserve the treatment they often get at the gardeners hand. Unfortunately these beneficial beetles breed relatively slowly compared with their prey. They have a very critical over wintering period when many die, for good control of pests it is essential that as many as possible survive overwinter. They try to find over wintering places in the Autumn (hence they are found scuttling around on the carpet in the house). In the garden little areas could be set aside as over wintering places. It helps to have loose materials or vegetation were they can hide. a few pots on their side stuffed with a strawy like material is ideal. In the bulb fields we maintain a broad rough grass strip around each field by the hedges each winter and most years we get quite good control from these beetles. We have had problems with an interaction with other predators some years but it has generally sorted itself out.

Aphids, Capsids and Leafhoppers                                                                                                                         If you are growing a large amount of lilies you will probably find them at some time. Several of the commoner Aphids (Greenfly/blackfly) may attack lilies. Not all species will attack these plants. These insects can travel considerable distances by flying or being swept in the wind, most of these insects can live of quite a range of host plants and so are often quite widespread. They suck the sap of host plants and can cause distortion of the growing plant especially while the plant is actively growing (Spring). In addition to possible physical damage caused, sap sucking insects can also transmit viruses from plants they were previously feeding on. It is fortunate that many of the most damaging viruses are specific to Lilies or related plants and therefore if Lilies are grown in separate groups it will reduce the risk of spread. Perhaps the most likely source of serious virus infection is from other Lilies or Tulips. The most commonly transmitted non native virus is Tulip Breaking Virus. It is not a native virus and has a very restricted host range, and therefore is most unlikely to get a toe hold in the wild. Its chief source is from Tulips brought in from tulip growing areas. Some infected tulips do not show symptoms but others do. All Rembrandt Tulips or other “broken” or striped tulips are probably infected. Keep these well away from your lilies. Tulip Breaking Virus can probably also be transmitted by some Fritillarias. The most frequently found virus on lilies (I believe) is cucumber mosaic virus this is common in most gardens and on a wide range of plants. Most strains of this virus have a relatively mild in effect on most lilies. it is possible there are more aggressive strains out there. It appears from some work that the presence of a milder strain of Cucumber Mosaic Virus already within a plant can help reduce the effect of a more aggressive strain trying to infect the plant later. Research has shown that spraying crops against aphids actually has little effect on the spread of aphid spread virus, however when plants are grown in a complex mix, such as in a garden, reducing the numbers of Aphids may have a beneficial effect (!). Aphids can be controlled by a wide range of insecticides some of which are available in Garden Centres. Aphids have developed a resistance to some insecticides. Older insecticides kill by contact or by systemic action, and can have a relatively broad action sometimes killing non target insects, systemic insecticides are normally very effective in controlling sucking insects. Newer insecticides are often more targeted and have less effect on other wildlife. Some other chemicals have some insecticide effect such as Soft Soap and Vegetable Oil. Soft Soap sprays can break the surface tension of water down and under damp conditions effectively drown the pests. We use vegetable oil in water (from Rape seed oil) this possibly suffocates the insects or puts them off feeding. There are a large number of natural predators of Aphids and biological control is a practicality. Small insectivorous Birds help keep aphids under control (ie tits, dunnocks).). In recent years the high levels of parasitic wasps have been our number one predator of Aphids. Ladybirds are voracious feeders of aphids. The larvae of hover flies are a useful addition particularly later in the season. Some Capsids (shield bugs) will attack lilies but rarely build up into any quantities. Leafhoppers can be a problem and can damage the leaves and flowers. Generally the controls for Aphids will control these.

Problems which are usually localised but can be quite damaging

Soil Borne fungi - section not complete

Lily Beetle (Lilioceris lilii) This pest was introduced by man some time ago to the UK but has been restricted to a small area around Wisley for many years. Thanks to improvements in transport and more people moving infected plants around the country, man has successfully spread it to new areas. In some areas these new colonies have died out and but have or may be reintroduced at any time.                                                                                                      Symptoms of damage leaves eaten, flower buds eaten, stems eaten. Damage is generally very noticeable giving the plant a very ragged appearance. Larger colonies will strip an entire plant quickly and eat the stem right down to the ground. Both the adults and the larvae eat lilies. The host range of this pest is so restricted that it has difficulty in spreading to new areas especially in Country areas. The adults are weak and reluctant fliers and hunt for new food plants by scent. Host range is restricted to a few genera. The actual host range is under dispute but all true lilies, some Fritillaria, Nomacharis, Notholirion, Convallaria, Polygonatum and Smilax may be potential hosts. A policy of zero tolerance of this pest should be the norm. This is a practical option because of its host range. It may be difficult to achieve initially if you have close neighbours who are growing lilies and are taking no action against this pest, however if no action is taken your neighbours lilies will all die out and so will the source of your problem.                        Recognising the pest. It is best for the untrained eye to be on the look out for something that looks a bit like a ladybird or bird droppings on your lily especially near were leaves, buds or stems have been eaten. The adult beetle at first glance looks a bit like a ladybird. It is red without the black spots and has black legs and at about 7-8mm long is a bit longer than the presently common 7 spot ladybird. The body is slightly elongated compered with a ladybird. The legs antennae head and underparts are glossy black, in fact as beetles go it is quite a handsome devil, cannot be said of the juvenile larval stage which spends most of its life covered in its own excrement! (hence the “look for bird droppings”) The grub inside the dropping looks more like a blowfly larvae and is generally orange when exposed. Covering itself with excrement is about the best camouflage you can get to protect yourself from insectivorous birds. The eggs, larvae and adults live on the above ground parts of the lily. The chrysalis stage is below ground. The author however has observed adults when disturbed may drop to the ground and actively hide themselves underground.. The adults can be fairly active and if they feel they are under attack can scuttle around to the other side of the leaf or stem. They can also emit a high pitched squeak which acts as a warning to other lily beetles to go for cover. This squeak is normally only heard above the background noise in quieter areas and when there is little wind. The pest does not attack the bulb. It is most likely to be introduced to new areas by transporting lilies with foliage or growing in compost.                       Control natural predators, particularly birds may check populations. there are several native predators which may have some effect on this pest. At present I know of no biological control which might be absolute. Hand picking of adults and the “bird dropping” juveniles on a regular basis over a period of time can give complete control especially if you only have a few lilies, but also remember to check related plants for beetles as well. Insecticides may be an option if you have a larger number of lilies and a more advanced outbreak (Ie you find both adults and larvae). Systemic insecticides are not likely to be very effective as they are biting insects and not sucking insects The insecticides which are most likely to be effective are the ones which work by contact or are stomach poisons. ones which have at least some persistence IE at least a week are likely to be more effective. We have limited personal experience of this pest we had a small outbreak a few years go, almost certainly deliberately introduced by some well intentioned individual (if you are reading this - thank you for the opportunity to gain experience of this pest, and breaking a period of over ten years when we have sprayed no insecticides on our field grown lilies). We sprayed the effected lilies and all other lilies within about 300ft with gamma BHC (lindane) in vegetable oil adjuvant (codacide) to increase persistence and reduce the amount of insecticide needed. A week later although we saw no signs of activity but we still gave a second dose. This eradicated the pest. I believe that many other insecticides may be effective possibly one of the more persistent pyrethroids such as Permethrin might be quite effective. Almost certainly it would be advisable to repeat the application 7-14 days later and subsequently keep your eyes open for signs of activity. At present many insecticides are being withdrawn from the UK market because of the cost of the licence required. The insecticides being withdrawn are not necessarily the most dangerous and the ones remaining are not necessarily the safest. In any case always treat insecticides with respect and follow instructions on the pack.

Lily Thrips (Liothrips vaneeckei) This thrips spends most of its life below ground and has no wings therefore it is incapable of spreading to new areas without mans help. Only the bulb is effected the pest feeds at the base of the scales causing brown spots. Most of the damage is probably due to secondary infections. Plants may lack vigour, look sick or quickly collapse. There is no sign of pest above the soil. In the soil or attached to the plant very small white insects can be seen, moving fairly slowly. With a hand lens or with very good eyesight on closer inspection these insects are elongated in shape with three pairs of legs, and look like typical thrips but without wings. The adults are generally more difficult to see but appear a shiny silver and are faster moving, again they look like thrips but have no wings. It is not known how widespread they are but it is likely to become more common with open borders between countries. Although they effect lilies it is possible they have a wide host range if neccessary, they possibly can effect most “bulbous plants”. It is possible these insects have some natural predators. Dipping the bulbs or drenching the plants in insecticides may give some control. A number of insecticides in the past have been used quite successfully but many are now not available. It is possible pyrethroid insecticides will give some control, or any insecticide which is effective against thrips, leafhoppers or aphids.

Vine Weevil , Millipedes, Wireworms, leatherjackets, chafer bugs                                                                                         Millipedes (looks like a slow moving centipede but with more legs and slow moving), Wireworms (orange/yellow grubs) and leatherjackets (grey coloured grubs) can do damage to the roots and bulbs of lilies and cause secondary infections. They tend to be localised and because they are not usually present in large enough numbers in a given volume of soil bulbs are not usually killed. Symptoms roots are eaten bulbs are holed. There are a whole host of natural predators already mentioned. Wasps as well have some effect particularly on leatherjackets (Cranefly larvae). Cockchafer grubs will attack bulbs but usually they are just a nuisance.                                                                                              Vine weevil has been around for some time, however it rarely attacked lilies until a few years ago. In its current form some circles it is believed to be a man introduced alien probably from Europe. Since the Garden Centre boom of potted plants and the regular import of large quantities of potted plants with compost from Europe their has been a sudden change. This pest has miraculously developed a taste for almost anything put in front of it, including lilies. Even so their does appear to be some differences, damage does appear to be more frequent on container grown lilies in a peat based compost, slightly less on containers with soil based compost and least frequent in the ground. This may be due to natural predators. The larvae which probably do the most damage live in the ground and eat plant roots-any plant roots! and open the plant to secondary infections. The adult weevils eat leaves. smaller plants up to the size of lilies can have so many roots eaten that the plant dies of drought! larger plants -shrubs and trees may have so many roots that by the time the last root is eaten many more have already regenerated. Recognising the pest signs of its activity are the plant looks unhealthy and lacks vigour and may even wilt suddenly. Leaves of the lily or nearby plants may show scalloped edges as a result of the adult feeding. The adult is a small blackish weevil with a rounded abdomen and pointed head, because of its markings the beetle appear matt grey rather than black. It has no wings and is not a great walker, so spread to new areas is only with mans help. In recent years most plant producers have taken this pest very seriously and most growers now as routine treat all their compost with either a special insecticide or a biological pest control organism. The larvae live in the soil and are creamy white with a brown head. The insect is nearly always in a curved position. They breed possibly once or twice a year in this country. A weird thing about this pest is that all of them are female and genetically identical. They are believed to lay their eggs without fertilisation and do not need males. Although this has certain advantages for slightly quicker reproduction in the short term it does rather leave them open to attack and it may be within a few years a natural predator or a man made one might suddenly wipe the whole specie out. Control. These pests do have quite a fair number of British natives gunning for them. Thrushes, Blackbirds, Robins and most of the Crow family are particularly fond of the larvae if they can find them. Ground beetles and nematodes take their toll. In the garden/field it is possible to get adequate control except close to cyclamen. Parasitic nematodes can be bought which will attack the larvae and can give good control for up to one season, if applied as directed. There are also chemicals either mixed into or drenched onto the soil or compost, which can give good control in some cases into the second year from one treatment. Suscon Green, Imidacloprid.  Other insecticides will kill vine weevil but it is difficult to get the insecticide close to the larva in the soil, so a percentage will survive. Used as a soil drench Malathion, BHC (lindane), Parathion (illegal for some time now). The adult weevil can be killed by spraying with almost any contact insecticide, but it is difficult to kill all the adults. Hand picking of adults is usually not 100% effective either.

Sciarid Flies (Fungus Gnats) These are normally only pests under glass they probably only do minor damage on adult plants (!), most probably being caused by possible secondary infections. On seedlings and other small plants they are more likely to cause problems (!). In the scientific field there has been much dispute whether they do any damage at all. The opinion in the 1970s was that they did not eat growing plants at all, this was followed in the 1980s by the belief that if they did attack growing plants then it was because the compost was too wet. This was followed shortly by the belief that they would attack growing plants only if the compost was too dry. Perhaps connecting brain to eye might help some scientists. The main attack appears to be on the root hairs. They breed very fast and soon form clouds of flies. they are very small flies with black bodies which sit on the compost till disturbed. The young are small white maggots with dark heads. Lindane (gamma BHC) and Parathion are likely to give control but are now probably banned as a drench. Malathion, and systemic insecticides are unlikely to give control as a drench. We have tried permethrin, bifenthrin, rotenone (derris), pirimcarb, malathion and metasystox as a spray against the adults with no apparent effect. We have used a vegetable oil spray based on oil seed rape (Codacide) and this gives good control but needs repeated treatment. We have used nematodes to control sciarid but have had no useful effect with repeated treatments.