Pests And Diseases Of Clematis

There are very few pests or diseases that affect clematis on a regular basis - though every gardener dreads the appearance of clematis wilt. The other troublesome problems are those that affect other plants such as roses - aphids (greenfly), whitefly, red spider mite and mildew. All can be avoided or controlled very easily.

Pests

Aphids and whitefly: Aphids can be troublesome in the late spring or early summer, causing damage to the soft young top growth and marking foliage. Spray the plants with a proprietary pesticide -one recommended for roses will be perfectly adequate. Whitefly is normally less troublesome and generally only affects plants grown under glasshouse conditions.
Birds: In the spring small birds such as bullfinches often damage the swollen flower buds of the C. montana group and the leaf axil buds of large-flowered cultivars can also be attacked on occasion. The bird-scarers used in fruit orchards are not suitable for the small garden as the noise would not go down well with the neighbours.Though it is frustrating when the buds of a C. montana are totally destroyed, the problem is not generally a great one.
Earwigs: These can be quite troublesome, especially if the clematis is growing near to old buildings with brickwork or timbers that have cracks in them, offering ideal places for the earwigs to hide during the daytime. They will emerge at night to chew holes in the leaves of clematis or to attack young growth and bore holes into flower buds, often destroying the flower before it has opened. Chemical sprays are available but there is an old-fashioned method of control that works perfectly well. Stuff a small flower pot with moss or similar dry material and stand it upturned on a stick near to where the damage occurs. The earwigs will hide in the moss and you can then shake them out and destroy them by treading on them.
Mice: Mice have a habit of biting off pieces of stem at ground level to use for nesting material. The only notice the gardener generally gets of this is in the early spring when clematis stems are found collapsing for no apparent cause until the stems are found to be without their connection to the root system. To avoid permanent damage to the clematis, the extra-deep planting is a must as the plants will then regrow from below the soil level. Clematis which are being grown through other groundcover plants, such as dense heather, are more likely to be attacked by mice looking for nesting material during the winter months or early spring. If there are no cats to keep mouse numbers down, mousetraps placed in drainpipes among the heathers are one solution but in a large garden in the countryside this becomes a difficult job. However, if the C. viticella types are used as suggested to grow through winter-flowering heathers, they are extremely vigorous, producing plenty of stems from below ground level. Once the stems become thick, they are less interesting to the mice. If the mice do carry out some unintended pruning for you, there are benefits - the clematis will become more bushy and well-furnished at the base.
Rabbits: Rabbits destroy top growth, so preventative action is certainly needed if they are known to be in the locality. There are two ways to protect clematis. Land drainpipes made of clay blend in reasonably well with foliage and if lengths of about 45 cm (18 in) are upturned over the root crown the clematis stems will grow up through them. If rabbits do cause any damage it will be above the top of the pipe and the clematis will regrow from this point.
Red spider mite: Red spider mite normally affects clematis when the soil conditions are dry and red spider is having a good year. A severe infestation can be recognized by the top surface of the leaves becoming blotchy and paler in color; when the leaf is turned upwards the lower surface is generally found to be covered with pinkish-red spider mites. As the foliage and flower buds will become totally distorted, the clematis must be checked immediately if red spider mite is found on other plants. The most efficient control is by prevention rather than cure; use a pesticide recommended for roses.
Slugs and snails: These pests generally cause trouble during mild winters and early spring. They tend to graze on new growth and the fat leaf axil buds, sometimes removing them altogether. Use proprietary brands of slug destroyers or try the old remedy of placing a shallow tray or container filled with beer near the clematis. Surrounding the plants with abrasive material such as coal ashes does deter slugs and snails to some extent.

Diseases

Clematis wilt: This is the biggest problem that clematis growers face, though fortunately it attacks only the large-flowered clematis cultivars and not the species or their small-flowered cultivars. Clematis wilt is caused by a fungus called Phoma clematidina. Normally, the point where the fungus attacks the clematis is at or just above the soil level. The fungus appears to enter the clematis stem through a crack or at the point of some previous damage or weakness. Once it starts to grow it destroys the cells of the stem and blocks the sap from reaching any area above the infection, thus causing the stem to collapse, becoming black and then brown as it wilts. What may have appeared a perfectly healthy plant the day before can suffer total collapse literally overnight, though sometimes only one or two stems will be affected. Clematis wilt normally attacks plants in early summer, very often just when they are at the point of flowering, causing maximum disappointment to the gardener. Once wilt on a plant is discovered, the affected stems must be removed and burnt. The fungus may have been present in the soil before the attack and been splashed on to the plant by rain or during watering. Therefore, when the top growth has been removed, it is advisable to drench the base of any remaining stems and the soil area to a diameter of at least 60 cm (2 ft) around the plant. The fungicide to use is a Bio Supercarb (carbendazim) solution. This should help prevent the fungus spreading and reduce the risk of further attacks. If the clematis has been planted 6 cm (2 1/2 in) below soil level and has built up a root crown of growth buds below the soil, in most cases the plant will recover and grow away. When new growth appears, a programme of drenching should continue using the Bio Supercarb solution as described on the container to destroy any remaining spores of Phoma clematidina. When new growth has reached two to three nodes, say 23-30 cm (9-12 in) tall, the tip growth should be removed, encouraging it to break and produce more side shoots. It is important to get the new stems as woody as possible. They too should be carefully tied into their support so they are not damaged by wind or rain. As it recovers, the clematis should be treated as if it were newly planted from the point of view of pruning, feeding, watering and training. If a clematis persistently succumbs to clematis wilt it is best to dig it up, remove most of its soil, drench it in a solution of Bio Supercarb and replant it in a less important planting site. The plant will show you that it can perform and you will be rewarded with marvelous flowers where you did not really want them. The old clematis planting site can be replanted but it is advisable that the site is also drenched with the solution of Bio Supercarb to clean up any remaining fungal spores. The soil should be replaced with new soil or compost. If your garden seems prone to clematis wilt, replant with the C. viticella cultivars, such as C. viticella 'Blue Belle' which has masses of flowers (as do all the C. viticella types) but larger, at 8 cm (3 1/4 in) or more in diameter. The C. viticella types do not suffer from clematis wilt.
Mildew: Mildew generally affects the later large-flowering cultivars, such as C. 'Jackmanii' and some of its group. Of these, C. 'Perle d' Azur' can be badly affected some summers, as can C. 'Madame Edouard Andr�'. In some years C. texensis cultivars, particularly 'Etoile Rose' and 'Pagoda', can be covered in powdery mildew. As a preventative action - and it should be prevented as there is no cure once the mildew has taken hold - use the same spray as is recommended for roses. Only the later large-flowered clematis and the C. texensis types should be sprayed, as other late-flowering clematis such as the Meclatis Section and C. viticella and its cultivars are not normally affected.