| The most serious disease of clematis, a varied genus
consisting of about 250 species, is commonly called
clematis wilt. It is a stem rot/leaf spot disease caused
by the fungus, Ascochyta clematidina, which mainly
affects large-flowered clematis hybrids. Species
clematis, their cultivars, and small-flowered hybrids
are much less susceptible.
Symptoms and Diagnosis
The symptoms of clematis wilt are very defining and
include sudden stem collapse, often just as the
flower buds are about to open. Within just a few
days at most, the stem(s) and its leaves turn black.
Leaf veins often develop a purple coloration. One or
more stems of the diseased plant may be affected or
all aboveground parts of the plant can be killed
down to just below the soil level. Often, an affected
plant will recover after a year or two.
Life Cycle
A. clematidina can survive in soil surrounding
infected plants and may overwinter in infected plant
debris. This organism appears to be activated by
high humidity and favorable growing conditions
found in early summer. It produces slimy spores
which are spread by splashing water, careless
handling, and unsanitary pruning. They can attack
any part of a susceptible clematis plant which bears
some sort of wound. This fungus, however, does not
move systemically through the host; thus, it causes
only localized infections.
Integrated Pest Management Strategies
1. Choose a favorable planting site. Your site should
receive 6 or more hours of sun daily, contain rich,
well-drained soil with pH about 7.0, and be
relatively open to ensure good air circulation.
2. Select the most resistant plants. Species clematis
and/or small-flowered hybrids seem to be more
resistant than large-flowered forms.
3. Keep the clematis area free of plant debris on a
year-round basis. Take special care to avoid injury
to stem and roots since the wilt fungus requires a
wound to begin its deadly work.
4. Avoid damaging the roots. Do not cultivate the
soil around clematis plants and maintain
good mulch.
5. Give good culture. Maintain good growing
conditions to keep all clematis plants as stressfree
as possible.
6. Prompt removal of diseased stems. In the event
that plants become infected, cut diseased stems
just below ground level and destroy them. Spray
any remaining, healthy parts of the plant and
surrounding soil with a protective fungicide such
as myclobutanil. | 
