Clematis Wilt Disease: Identification and Treatment
While relatively carefree, clematis sometimes falls victim to a species-specific disease that causes quick wilting and dieback. Clematis wilt pops up right before the beautiful blooms open. Explore what the fungal disease looks like, as well as prevention, with gardening expert Katherine Rowe.
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Clematis are show-stopping with their vertical interest and flush of colorful blooms that line delicate, leafy stems. The long-lived vines have diverse flowering forms, colors, heights, and bloom times, with over 350 species and thousands of cultivars.
Beloved in the landscape, these low-maintenance perennials are easy to care for in the right environments. Sometimes, however, the vines experience pest and disease issues due to cultural or external factors.
Clematis wilt is the most severe among species-specific diseases. Fortunately, the vines are resilient and may overcome the disease if caught and managed in time. Here’s how to identify and treat it.
Clematis Growing Conditions
Clematis vines with strong root systems have the best resistance to pests, diseases, and environmental stress. The best conditions to promote sturdy roots and vines include:
- Planting in full sun to partial shade with protection from direct afternoon rays
- Keeping roots cool with mulch or coverage from surrounding plants
- Providing plenty of air circulation between plants and surrounding structures
- Planting in moist, well-draining soils
- Avoiding waterlogged or drought conditions
- Pruning vines according to type to increase airflow and encourage new growth
Clematis shows its full glory by its third growing season. In the first two years, they may “sleep” and “creep” as their extensive roots develop. By the third season, clematis “leaps” into graceful, full foliage with abundant blooms.
The twining leaves benefit from a support structure like a trellis, arbor, arch, post, or multi-trunk tree. Grow the perennial vertically for visual interest, and in pots as featured specimens.
Ensure airflow between the vines and surrounding structures, and prune plants according to whether they bloom on old wood, new wood, or both. Properly pruning the woody stems helps open plants for increased air circulation, promotes new growth, and encourages reblooming.
What is Clematis Wilt?
Clematis wilt is the most severe problem for the flowering vines. The pathogen Phoma (formerly Ascochyta) clematidina is a fungal disease specific to clematis stems and leaves. The fungi mainly affect large-flowering hybrids, with smaller-flowering selections showing more resistance.
The fungus causes leaves and stems to dry and wither, and specimens wilt quickly. Left unmanaged, clematis wilt spreads quickly and causes decline and dieback. Fortunately, the fungus does not attack root systems, with more localized damage to leaves and stems. With proper treatment, the affected perennials may recover in the following year or two.
Clematis wilt enters wounds in stems from rubbing against ties and supports, poor pruning, or whipping in the wind. The wilt spreads via leaf spot and splashing water.
Identification
If your clematis vines experience sudden drooping just before flowering, clematis wilt may be the culprit. As the fungus causes rapid drying and wilting, the stems fold quickly, often just before flower buds open. Affected portions turn black, leading to a quick decline if left unattended.
Clematis suffering from wilt may exhibit watery brown or black leaf spots and stem cankers. The impacted leaves may shrivel, and the stem will blacken, followed by wilting. Stems and healthy shoots also show clematis wilt infection through red lesions, discoloration, and splitting.
Treatment
There is no chemical control for clematis wilt once it sets in. The best action is to promptly remove impacted leaves and fallen ones, too. Cut back affected stems to healthy green and white flesh. Destroy or discard all removed plant parts rather than adding them to your compost pile.
If the clematis wilt infection is limited, the vines will produce new growth and shoots from the base. If new growth doesn’t emerge in the current season, cut all the stems back for a recovery period until the next growing season.
Cutback promotes healthy regrowth, though it may take a year or two to rebound.
Prevention
To prevent this specialized wilt, start with location. Position the vines in a spot with six hours of sunlight, in rich soils with good drainage, and with plenty of airflow.
Considering their delicate stems, it helps to check the supports for rubbing injury. Inspect support structures and ties during the growing season. Clematis need thin supports for the base of the leaves to cling to. The leaf stems twine and rest on supports about ¼ inch thick.
If clematis wilt becomes an issue or you have a history of the problem, consider growing resistant small-flowered or species varieties in a different location. Resistant clematis species and their cultivars include:
- C. alpina
- C. macropetala
- C. montana
- C. viticella
Preventative fungicides may help limit the spread of clematis wilt after removing diseased portions. Applications to healthy leaves, stems, and the surrounding soil may limit the emergence.
Plenty of Air Circulation
Clematis benefits from good air circulation around leaves and stems to prevent fungal problems like clematis wilt, leaf spot, and powdery mildew. Allow space between the vines and structures like walls, with their supports placed several inches away for ventilation.
Situate the vines so they’re out of strong winds that can break or injure the stems and create wound points for the fungus to enter. Drying summer and winter winds also cause stress, from the foliage to the roots.
Prune clematis according to whether they bloom on old wood, new wood, or both. Pruning woody stems helps open plants for increased air circulation, promotes new growth, and encourages reblooming. Know your type to determine the best pruning strategy.
Minimize Root Stress
Minimize root stress to promote resilient vines. Situate transplants in well-turned soils with room to grow. Well-turned soil minimizes stress on clematis’ sensitive roots as they slowly establish. Dig a hole twice as large and deep as the nursery pot, and at least a foot wide and 18 inches deep to loosen the surrounding soil.
Install the vine with the crown one to two inches below the soil level. This helps protect it for easy recovery in future seasons from animal damage, clematis wilt, and weather extremes.
The flowering vines prefer organic, well-drained soil. Amend with compost at planting to improve nutrition, aeration, drainage, and moisture retention. Clematis prefers even moisture, with one inch of water per week during the growing season (rainfall or irrigation) and supplemental water during dry spells.
Situate stems and leaves so they soak up the sun, while letting roots stay cool and moist. To protect the roots, provide a two-inch layer of mulch. Mulch helps regulate soil temperature and retain moisture. Bark chips, straw, and leaves work well as mulch material. Keep it off the stems to prevent diseases.
Low groundcovers and perennials also provide cooling shade at the ground level. Opt for those with shallow roots that won’t compete with the vine in close proximity. The leafy material helps insulate the roots and aids in moisture retention, too.
Good Garden Sanitation
Clematis wilt fungal spores overwinter in the soil and plant debris around infected specimens. Year-round, keep the bed free of fallen material, with a good sweep at season’s end to reduce overwintering.
When pruning clematis, use sharp, sanitized pruners to minimize stem injury and reduce the spread of disease. An alcohol wipe, a dip, or spray solution of 70% isopropyl alcohol does the trick. Remove diseased stems as soon as you spot them to keep the wilt localized.
