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.
- 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
- 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.
- 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 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 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
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.
- 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 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 André’. 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.