5 Common Clematis Diseases and How to Treat Them

Clematis is a favorite perennial and quintessential blooming vine. With over 350 species and thousands of cultivars, varieties boast numerous flower colors, sizes, and bloom times. With the right cultural conditions, the ornamental vine is an easy-care, long-lasting garden performer.

While clematis has few pests in the landscape, it is susceptible to common fungal diseases, including one especially fierce pathogen, clematis wilt. To help prevent disease, improve growing conditions by providing plenty of air circulation between plants and structures and adjusting watering methods and frequencies to allow for evenly moist soils.

Early detection helps plants recover from infections and prevents their spread. Here, we’ll explore common diseases among the flowering vines and how to treat and prevent them.

Setting Clematis Up For Success

Providing the best cultural requirements for clematis builds strong root systems and robust vines. In its first two seasons, plants may “sleep” and “creep” as their roots develop. By the third growing season, clematis “leaps” into graceful, full foliage with abundant blooms. Follow a few key growth preferences to keep them flourishing and disease-free.

Plants grow best in full sun, with at least six hours of sunlight daily. They’ll tolerate less, especially in hot climates, where morning sun and light afternoon shade protect leaves and stems from intense rays.

They prefer organically rich, well-draining soils for nutrients, moisture retention, and aeration. A layer of mulch helps regulate moisture and soil temperatures. 

The twining stems appreciate a support structure like a trellis, arbor, arch, post, or multi-trunk tree. Ensure airflow between the vines and surrounding structures. Prune plants 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.

Powdery Mildew

Powdery mildew is one of the most common fungal diseases and affects numerous plants, from vegetables to ornamentals, including clematis. The pathogen is Erysiphe. It presents as a grayish-white dusty substance on leaves, stems, and buds. 

Powdery mildew spores spread by traveling on the wind, contacting other plants or tools, or splashing up from the soil via raindrops and irrigation. The spores grow on the leaves and spread to the stems, depleting the plant’s energy and nutrition.

Clematis leaves may turn yellow, distort, and drop during severe infections. If left untreated, plants wither and eventually die. The fungus also spreads quickly. Fortunately, powdery mildew is treatable with early detection.

Treatment

If powdery mildew is isolated to leaves and you can easily pick them, remove the leaves and dispose of them in a garbage bag or burn pile.

For more extensive outbreaks, horticultural oils like neem or horticultural soaps can treat powdery mildew early in the game, and prevent spread of the disease to healthy leaves and stems. Organic elements in fungicides like bicarbonate may be practical. Be sure to follow application instructions, as these treatments impact beneficial insects visiting plants for nectar or pollen. Time of day is important in using products effectively. A light mist is enough. There’s no need to soak the plant with fungicide or oil.

Prevention

Water plants at their base to avoid splashing foliage, which transmits spores and promotes their ideal environment. Avoid overfertilizing – clematis are heavy feeders and appreciate a balanced fertilizer in spring. Too much nitrogen leads to weak, leafy growth susceptible to disease. Prune regularly for proper air circulation.

Leaf Spot

Leaf spot is a fungal infection that manifests on leaf surfaces. Brown spots with tan centers become more significant and spread across leaves and stems over time. The fungi cause affected leaves and stems to blacken. 

The brown or black spots occur when leaves remain overly wet from overhead watering or prolonged periods of moisture. Several pathogens, including Phoma (formerly Ascochyta), Botrytis, Cercospora, Cylindrosporium, Phyllosticta, and Septoria, may cause clematis leaf spot.

Detecting leaf spot early is the best control, with diseased leaves easily plucked from stems. Phoma leaf spot can lead to wilt, which is specialized to clematis. It causes a sudden decline in leafy, budded stems. 

Treatment

To treat leaf spot, remove damaged leaves, including any fallen leaves. Prune the vines and surrounding plants to increase air circulation. 

If growing clematis in containers, give them space between other pots and structures like solid walls. Continue to scout regularly to remove any affected leaves as spots crop up.

Prevention

The best way to prevent leaf spot is to provide ample air circulation around clematis leaves and stems. To minimize damp conditions, water the vines at the ground level rather than spraying the leaves. If spraying the plants with water is necessary to deter pests, do so in the morning or midday, when the leaves will have time to dry in the sun.

Rust

Rust is another common fungal disease most prevalent in hot and humid climates. Sections of the vines may swell and blister. Leaves may yellow, wilt, and drop early. 

Another sign of rust is powdery spores on the undersides of yellowing leaves. The spores erupt with yellow mold caused by the highly specialized pathogens Aecidium and Puccinia.

Treatment

Cut off the infected leaves and other plant parts if you see rust. Rust spreads readily, so discard the infected plant parts away from garden areas.

Horticultural oils like Neem and preventative fungicides can treat fungal diseases early on. Removal is the best option for any severely impacted garden plants in decline.

Prevention

As with leaf spot, the best way to prevent rust is to increase air circulation between plants, especially in humid conditions. Watering at the base of the plant delivers moisture to the roots without impacting foliage.

Root Rot

Fungal root rot causes plants to decline slowly. The pathogens behind root rot are Phymatotrichopsis or Phytophthora. The fungi impact feeder roots, preventing them from uptaking water and nutrients. Leaves appear drought-stressed and may turn yellow as they wilt.

Clematis is prone to root rot. If your vine is wilting or dying, there may be a few reasons, including root rot. Check for rot slightly below the soil line. If it’s affected by rot, clematis stems will be yellow, and the roots will be brown rather than a healthy white.

Treatment

If caught early on or with minor damage, plants can recover. Reduce the irrigation frequency to allow soil time to drain. Keep it evenly moist but not overly saturated. 

If necessary, improve soil drainage by repotting container specimens, cultivating the soil around existing plants, or lifting and replacing plants on higher, mounded soil.

Prevention

Proper cultural management, especially not overwatering, is the best control. Ensure soils are well-draining. While clematis thrives in evenly moist soils, oversaturation and soggy soils can lead to disease. 

Water deeply and increase frequency between sessions if needed. However, deep, infrequent watering allows better absorption over frequent, shallow watering. Allow plenty of airflow between plants and surrounding structures.

Clematis Wilt

Clematis wilt is the most severe plant problem. The pathogen Phoma (formerly Ascochyta) clematidina is a fungal disease specific to clematis stems and leaves. The fungi mainly affect large-flowering hybrid varieties, with smaller-flowering selections showing more resistance. 

Plants wilt quickly as the fungus causes leaves and stems to dry and wither. With this particular wilt, stems fold quickly, often just before flower buds open. Stems and leaves turn black. Left unattended, the disease spreads quickly and causes decline and dieback. 

Good news: affected plants may recover in the following year or two. The fungus does not attack root systems. Clematis wilt spreads via wounds in stems from rubbing against ties, supports, or whipping in the wind. Plants have delicate stems, and it helps to check supports for rubbing.

Plants suffering from wilt may show dark brown and black leaf spots and stem canker. The impacted leaves may wither, and the stem will blacken, followed by wilting. Stems and healthy shoots also show infection through discoloration and splitting.

Treatment

There is no chemical control for clematis wilt. The best steps are to remove impacted leaves and fallen ones, too. Cut back affected stems to healthy green and white flesh. Destroy all removed plant parts and sanitize your shears after treating.

If viable after the infection, the plant will produce new growth and shoots from the base. Otherwise, cut plants back for a recovery period until the next growing season. Healthy growth may take a year or two.

Prevention

To prevent this specialized wilt, start with plant siting. Grow plants in a spot with six hours of sunlight, in rich soils with good drainage, and allow plenty of airflow.

Minimize root stress on plants—situate new vines in well-turned soils with room to grow. Add a layer of mulch, keeping it away from stems to prevent rot.

If wilt becomes an issue, consider adding resistant small-flowered or species varieties in a different location. Resistant clematis types include C. alpina (purple), C. macropetala (blue), C. montana (pink), and C. viticella (purple) and some of their cultivars.