This page is abridged from an article written by Dr Chris Clennett for the Cyclamen Society Journal Vol 42-2 December 2018, with the availability of pesticides updated as necessary.

The title of this page may appear daunting to those growers relatively new to cyclamen, but we have one phrase for you – don’t panic!

Although cyclamen can be attacked by some difficult-to-control foes, overall they are generally fortunate to be prone to a relatively small set of pests and diseases.

Pests

• Vine weevil
• Eelworms
• Caterpillars
• Cyclamen mite
• Two spot mite
• Clover mite
• Aphids

Diseases

• Grey mould
• Root rots
• Damping-off diseases, mildews and wilt diseases

Pests

Vine weevil (Otiorhynchus sulcatus)

The adults of this pest are largely nocturnal beetles around 1.5 cm (0.6 in) in length, and of dark grey coloration. The adults nip semi-circular sections of leaf margins as they feed, rather like those of solitary bees, so their presence is often overlooked. They rarely, if ever, feed on cyclamen, preferring larger thin leaves like vines (hence their common name), kangaroo vine, grape ivies (Cissus and Rhoicissus species), rhododendron and lily-of-the-valley (Convallaria).

Damage to cyclamen caused by vine weevil is frequently undetected until the afflicted plants are beyond recovery, since the larvae of the beetle feed on the roots and tuber. This leads to the abrupt collapse of the top growth when water and nutrient supply is cut off.

The grubs themselves are white with a noticeable brown head, and are about 0.5 to 1 cm (0.2 to 0.4 in) in length. They adopt a characteristic sickle or ‘C’ shape when removed from the soil and, if observed closely, are seen to be coated in short stiff bristles. If the host plant survives for sufficient time and the infestation remains unnoticed, they will pupate after three months, becoming ghostly white versions of the adult but still underground. 

Adults emerge during two main periods, in autumn or the following spring, by burrowing up to the soil surface. They are extremely vulnerable at this stage since their external skeleton has yet to harden, but unfortunately they emerge only at night when potential predators (including gardeners) are unlikely to discover them.

Control of vine weevil is difficult and rarely completely successful. Some adults invariably remain to cause a fresh infestation and, since each female can lay up to 1,000 eggs in its four-month life, the potential for serious damage should never be underestimated. 

Over the last 30 years or so, almost all pesticides effective against vine weevil have been withdrawn, including aldrin, HCH (lindane) and, in 2016, chlorpyrifos. Recent concerns over neonicotinoid insecticides and bee health mean that imidacloprid and thiacloprid, are no longer available in the UK. 

An alternative to chemical insecticides is to use nematodes. Nematodes, also called eelworms, are small (mostly microscopic) unsegmented worms. They are extremely numerous in the soil, where the majority of species are detritus feeders, but some are plant pests and a few are parasites of insects. These insect-attacking nematodes have been developed commercially as a means of controlling vine weevil. The nematodes attack weevil grubs by burrowing into their body, where they release a biological weapon in the form of a bacteria. The bacteria poison the grub, causing its death within a few days. The nematodes feed upon the remains of the insect, reproduce and the cycle is completed when the young nematodes leave to search out another host. 

Eelworms

The nematodes that attack vine weevil may be our friends, but there are others that most certainly are not. 

Root knot nematodes (of the genus Meloidogyne) are more of an issue for cyclamen. They are less fussy in their choice of host plant and cause the development of lesions and swellings throughout the root system.

Cyst nematodes (of the genus Globodera) cause small spherical cysts to develop on the roots of their host plant, giving them their name, but cyclamen are generally immune. 

This, in itself, impairs the plant’s growth and can also lead to infection by root rot and wilt fungi, leading to the death of the plant.

Control is almost impossible without sterilising soil, so destroy any infected plants and do not replant in the same part of the garden. Infestation is much less likely for container grown plants, in soil where the nematodes can move from there to the pots. Where cyclamen have become victims there is usually nothing for it but to destroy any affected plants.

Caterpillars

Several species of moth caterpillar attack cyclamen, along with a wide range of other host plants. Because most cyclamen are dormant in summer, those species of caterpillar active over the summer months are not usually a problem, but those moths with active caterpillars in winter can cause damage. Three moths in particular may attack cyclamen leaves.  

Angle shades moth (Phlogophora meticulosa) is a large moth with characteristic mottled brown wings held at 45° angles to the body when at rest. The caterpillars grow up to 4.5 cm (1.8 in) in length and may be green or mixed shades of brown, sometimes with hints of yellow. The head colour varies from green to mottled brown and a fine, pale dorsal line runs down its back. A broad pale band extends along the side of the body.

Caterpillars pupate in leaf debris or loose soil. In winter, they eat almost any evergreen plant they come across, creating ragged holes and tears at the margins of leaves. They tend to be nocturnal, so the first indication of their presence is usually the damage but no sign of the culprit. Their damage can sometimes look very similar to that of slugs and snails, but the characteristic slime trails of the latter are absent, giving a clue to the cause.

Carnation tortrix moth (Cacoecimorpha pronubana) and Cyclamen tortrix moth (Clepsis spectrana) have much smaller adults and the caterpillars are similarly much smaller than those of angle shades moth.

The main difference, however, is in their method of feeding. Being small and vulnerable, they protect themselves by spinning silk webs, which they use to ‘tie’ leaves together and create a protective tent. From within their lair, the caterpillars eat the leaves they have fixed in position, until eventually pupating within the tent and emerging as adults. Damage can be quite severe in some plants, and as they are also active over winter, any evergreen is vulnerable, especially in a greenhouse. Given that young emerging cyclamen leaves are already folded in half, they make an ideal home for tortrix caterpillars.

Control of caterpillars is usually best attempted either by picking off individuals as found, or where infestation is severe by insecticide treatment. Try sprays of pyrethrum or synthetic contact insecticides such as deltamethrin or cypermethrin.

Cyclamen mite
(Phytonemus pallidus)

(Syn. Tarsonemus pallidus, Steneotarsonemus pallidus)

This minute pest attacks several genera as well as cyclamen and the symptoms can often be seen on Impatiens (Busy Lizzie). Here, the shoot tips become blackened and distorted and the meristem or growing point rapidly dies. In cyclamen the symptoms follow a similar pattern, with deformed and discoloured growth. Flowers fail to develop properly with the flower stem twisted and the petals puckered.

The pest itself is a white to brown mite, 0.25 mm (0.01 in) long, too small to see with the naked eye. In cold glass, infestation is likely only during summer and it is infected material brought on to site that usually causes an outbreak.

The mites spread by crawling from one plant to another and, bearing their size in mind, the rate of dispersal is obviously slow.

Control is primarily achieved by thorough investigation of all new plants brought into a collection or nursery, always remembering that other plants can be infested as well as cyclamen. However, once an outbreak has been noticed remedial action becomes more difficult. Unfortunately, there are no effective chemicals available to the amateur and the only solution I have been able to find is to use hot water treatment. This consists of immersing the entire plant in water at 46° C (115° F) for seven minutes, where the temperature and time are critical. This must be a last resort, however, and rigorous prevention can avoid this situation.

Two-Spotted mite (Tetranychus urticae)

This pest is more-widely known as red spider mite and can occasionally prove troublesome to cyclamen. It is a small mite about 0.5 mm (0.02 in) long and variable in colour from green to red (it is only red when dormant, hence the inappropriate nature of the old common name). Symptoms of attack are yellow speckling on the leaves and defoliation if allowed to persist. If severe infestation is allowed to go unchecked, the pests produce webs, which cover the growing tips of affected plants.  In cyclamen, webs tend to be found around the margins of leaves. The mite is extremely resistant to chemicals and although some degree of control is possible with systemic pesticides, frequent repeat application is required to maintain control. 

Biological control is possible using the South American predatory mite (Phytoseiulus persimilis) which will maintain control so long as the temperature remains above 18° C (64º F). This means it is of little use on cyclamen except under glass during summer and even then, since the plants are losing their foliage naturally, the use of this predator is of doubtful value. However, since the use of the predator will keep two-spotted mite populations down over summer, where cyclamen are grown in greenhouses this would reduce the chances of infestation when plants come into leaf in autumn.

Clover mite
(Bryobia praetiosa)

Bryobia is a genus of mites in the spider mite family, Tetranychidae. They are among the largest of the spider mite family at 0.75–0.85 mm (0.030–0.033 in) long, oval shaped with a pair of long legs pointing forward. 

The taxonomy of these pests is difficult and the genus has been revised several times. It is difficult to distinguish these tiny species from each other on the basis of morphological characters, and there is little agreement on which characteristics are of importance. Those that seem to be quite prevalent amongst cyclamen collections in the UK at the moment are blackish-brown to dark reddish brown with red legs, the eggs are spherical and bright red in colour, usually laid singly on the underneath of the leaf, often around the leaf sinus.

The adult mites are visible with the naked eye, but a 10x loupe is useful when looking for the eggs.

Symptoms of attack are similar to spider mites with yellow speckling on the leaves and defoliation if allowed to persist, unlike spider mites Bryobia do not produce webs.

Some degree of control is possible with sprays of pyrethrum or synthetic contact insecticides such as deltamethrin.

Aphids

There are four principal aphid species likely to be troublesome to cyclamen growers, although with around 500 species recorded in the British Isles it is not impossible that others will be encountered. The main culprits are: 

Peach-potato aphid (Myzus persicae)

Cotton-melon aphid (Aphis gossypii)

Apple-grass aphid (Rhopalosiphum oxyacanthae)

Mottled arum aphid (Neomyzus circumflexus, syn. Aulacorthum circumflexum)

Since most aphids follow a similar life-cycle and respond to similar control methods it is easiest to describe a generalised case with reference to any anomalies which occur. Incidentally, the common names given above indicate the main host plants of each aphid species, although by no means the only host plants. 

Unless conditions are exceptionally mild, or artificially heated, all aphids overwinter as eggs laid in crevices by the last generation of females in autumn. In some species, males are produced by the preceding generation and the fertilisation of the eggs causes their dormancy. These will hatch in spring to produce a wingless generation of females that begin to feed and to produce live offspring parthenogenetically (that is, without fertilisation). As the population builds up, hormonal changes cause winged females to be produced which migrate to other plants. In the case of species with two host plants, winged females are produced probably by day-length stimulus and migrate to the summer host. The population then expands exponentially until food shortage stimulates further dispersals throughout the summer.

Two-host species will then migrate back to the winter host crop as day length shortens. Control of aphids is usually carried out by the use of quick-acting contact insecticides that are specific in their action, or by systemic insecticides for long-term protection of the plants.

Biological control is now also a practicable possibility with the advent of several predators and a fungus. The fungal control agent is Verticillium lecanii which is applied as spores. These germinate and infect the aphid with hyphae (fungal strands) causing its death in about two days. As the dying aphid moves through the colony it spreads new spores to other individuals. Unfortunately, the fungus requires a minimum temperature of 15° C (59º F) and high humidity to maintain control so it is only of use on pot-plant cyclamen.

Although damage to cyclamen is seldom severe in the case of aphid attack, the pest can carry several types of virus so that early control is essential, especially where a commercial crop or rare species is grown. 

More universally successful biological control is feasible using a predatory midge (Aphidoletes), or a parasitoid brachonid wasp (Aphidius matricariae). Larvae of the midge are voracious predators and will seek out aphids in inaccessible sites, thus giving excellent control. The brachonid wasp Aphidius isa native insect very similar in appearance to the chalcid wasp Encarsia used to control glasshouse whitefly. It lays eggs into the body of an aphid, which then gradually changes to a straw colour and enlarges until almost spherical, due to the action of the wasp larva developing within it. 

Diseases

Grey Mould (Botrytis cinerea)

Grey mould is potentially one of the most serious diseases that can attack glasshouse plants and particularly cyclamen. It is encouraged by damp still conditions and by low temperatures, and is most often encountered during autumn and winter. The disease is caused by a pathogenic fungus of the group known as Fungi Imperfecti, meaning that it never produces resting sexual spores. Survival through periods of adverse conditions is achieved by sclerotia which are resistant bodies produced underground.

These can survive several years and will germinate to produce new fungal strands or hyphae as soon as moisture is present. Spread of the fungus is by means of asexual spores produced on branched structures known as conidia, and these spores are thus termed conidiospores.

They do not survive for long, which is why as soon as conditions become too dry in spring, the disease stops spreading. Conidiospores germinate on contact with moist leaf surfaces and penetrate directly into the plant.

A network of fungal hyphae rapidly develops which secrete cellulolytic and pectolytic enzymes, causing the plant tissue to dissolve into a gelatinous mass.

As the plant tissue breaks down, the fungus is stimulated to produce masses of conidia from which the spores are released, resembling a grey cloud of dust when a slight breeze catches them.

Control is achieved by cultural and chemical means. Using a free-draining compost and maintaining maximum possible ventilation will discourage the disease, while ensuring glasshouse hygiene will prevent the fungus from surviving in debris or the glasshouse soil. Botrytis is a facultative parasite and can grow in much the same way as mushrooms when a host plant is unavailable, thus making hygiene of vital importance in its control. Chemical control is not particularly easy for grey mould as it develops resistance to sprays remarkably rapidly. However, several chemicals are available and if used in a rotation of two or three, resistance is unlikely to build up. 

Root rots (Thielaviopsis basicola, Cylindrocarpon destructans)

Root rots are again fungal diseases of the Fungi Imperfecti type. They are encouraged by damp conditions and in pot-plant cyclamen are a primary cause of loss among purchasers where overwatering is common. These fungi are present in all soil and under suitable conditions will invade plant tissues just below ground level. They usually require a damaged site to enter the plant and for this reason healthy plants are rarely affected. Lesions develop on the roots followed by decay of the outer root tissue, leaving a woody core.

Examination of infected plants will show wiry blackened roots as the softer tissues have broken down. As the plant fails to obtain water and nutrients through the damaged roots, top growth begins to wilt and other fungi gain entry causing the leaves to brown and wither.

Control is best attempted by using sterilised composts and ensuring adequate drainage. If plants can be kept healthy and growing vigorously these fungi are unlikely to become a serious problem. 

Damping-off diseases, mildews and wilt diseases

There are several fungal diseases that affect a wide range of plants and can become troublesome for cyclamen. Like many fungal diseases, these organisms tend to attack vulnerable or weakened individuals, suffering from stress in some way, so keeping your plants as healthy as possible is a good first step to avoiding trouble. 

Damping-off diseases (Rhizoctonia solani and Pythium species)generallyattack only seedlings and this is the case in cyclamen. Rhizoctonia can also cause other problems such as stem and collar rot in poinsettias and other house plants, where damp compost encourages the fungus at the surface. Symptoms show as the petiole collapsing in germinating seedlings. On close investigation the tissues of the petiole will be found to be black where Rhizoctonia is the culprit, or brown where Pythium has attacked the seedlings. Secondary rots frequently then invade as the stem collapses and these lead to the death of the seedling. It is extremely difficult to control both of these fungi and as they are members of different fungal groups certain identification needs to precede use of chemicals. 

Downy mildews (of the genus Peronospora) are in the same fungal group as Pythium. Until recently, downy mildew would not have been considered a disease of cyclamen. 

In cyclamen, the fungal mycelium resembles a white web with occasional white grains on the threads. Commencing as a 1 to 2 cm (0.4 to 0.8 in) spot on the underside of the leaves, it will gradually spread to cover the whole leaf within some weeks.

Once the Peronospera has attacked the whole plant, the leaves will curl downwards on themselves and the disease becomes visible over the whole leaf, not just the underside. Later the white mycelium develops a purple hue.

The fungus thrives in warm, damp conditions, so keep greenhouse conditions as cool as practicable (preferably below 9°C/48°F) and keep humidity low by opening vents and doors whenever possible.

Control of downy mildew is difficult, but this fungus is related to Pythium and Phytophthora (the latter being the cause of potato blight). This means the same chemicals can sometimes control downy mildew and damping-off disease. Propamocarb hydrochloride can be effective against both and this is approved for use against Pythium in damping off disease. Chemical control of Rhizoctonia is also difficult, so cultural methods are vital.

Wilt diseases (of the genera Fusarium and Colletotrichum) grow in the tissues of plants, but their damage is caused when they develop masses of hyphae (strands) within the water transport system of the host plant (the xylem tubes). The mass of hyphae causes a blockage or tylosis in the water system and result in a cut-off of water supply to leaves and shoots (or entire branches in trees or shrubs). This is the reason for the name wilt fungi, as the first obvious symptom of disease is large areas of the plant wilting through lack of water. Most wilt fungi are distributed over short distances by surface water, or more frequently by growers moving infected plants from place to place. 

Fusarium and Colletotrichum cause similar disease symptoms in cyclamen. Areas of the leaves, or more frequently the stems, become blackened as they die and wilt symptoms develop above this point. If growing points are attacked, they may recover with swift treatment but, for commercial cyclamen production, any level of damage is often economically unrecoverable.

These fungi can also cause anthracnose diseases in various plants, including cyclamen, in which the fungus causes dead patches or lesions to develop. These are usually black and can appear on leaves, stems or fruit. The fungus destroys the tissues it is feeding on and then generates spores from the surface of the lesions, spreading to further parts of the plant and to neighbouring specimens. Chemical treatment is difficult, as most effective products are no longer available to amateur growers within the EU. The same groups of active ingredients as for downy mildew and damping-off disease may be effective, particularly for Fusarium infection. Try a systemic fungicide if problems occur, but often the only solution is to destroy affected plants and avoid replanting in the same garden area. If infection occurs in a greenhouse, dispose of the pots as well as the plants affected to avoid spreading the fungus.