Tips on how to use this section
The symptoms of the most common problems are in the left column of the chart. In the right column are the probably causes of those symptoms. For those problems for which there is detailed information in a different part of Yardener’s Helper, the name of the problem is linked to a detailed file. For those problems for which there are no additional files, the discussion is found in the paragraphs below the chart.
| Solving Clematis Problems | |
|---|---|
| Symptoms | Probable Causes |
| Stem Injury Tops Die Back | Stem Injury |
| Leaves and Flowers Eaten | Blister Beetles |
| Vines Stunted | Clematis Borers |
| Leaves Yellowed | Soft Scale |
| Plants Stunted; Yellowed; Root Lesions | Nematodes |
| Stems Girdled; Foliage Dies Back | Clematis Wilt |
| Leaves Covered With Gray Powder | Powdery Mildew |
| Leaves Spotted or Blotched | Leaf Spot |
| Stems Gnawed Through | Rabbits |
Stem Injury Tops Die Back due to Stem Injury
Any serious injury to brittle clematis stems, such as from a lawn mower, cultivator or the family pet, causes its tops to die back. Protect stem bases with a collar of wire mesh, 18 inches high and up to 10 inches in diameter around the base of the plant. Set it 2 inches below the soil surface.
Leaves and Flowers Eaten Blister Beetles
Adult clematis blister beetles are gray with a yellowish tinge. About 3/4 inch long, these slender insects have soft, flexible wing covers. Swarms of these beetles chew flowers and leaves, devouring almost everything in sight. The best quick defense is to handpick the insects. Wear gloves. True to their name, these pests secrete a substance that painfully blisters the skin. If a heavy population has infested your clematis, spray the beetles weekly with a solution of pyrethrum and rubbing alcohol, mixing 1 tablespoon of alcohol in 1 pint of pyrethrum.
Vines Stunted Clematis Borers
These borers, the larvae of clear-winged moths, are dull white worms with brown heads. They are about 2/3 inch long. They winter over in the roots. In midsummer, they hollow out stems and tunnel through the crown and roots of the plant. Clematis vines may become stunted and their branches die. Control the pests by cutting out and burning infested stems. Remove the soil carefully from around the crown of the plant and dig out any visible larvae. For more information see the file on Controlling Borers
Leaves Yellowed Soft Scale
Soft scales are especially fond of clematis. These pests form small bumps on leaves and stems. The bumps are waxy shells that protect the sap-sucking insects beneath. They are oval in shape, and vary from greenish to brown in color. If clematis leaves begin to turn yellow, suspect scale. Look for the telltale bumps and scrape off small infestations with a fingernail or a cotton swab dipped in rubbing alcohol. Heavy infestations are more easily controlled by spraying the scales with a mixture of alcohol and insecticidal soap for every 3 days for 2 weeks. Add 1-tablespoon alcohol to a pint of ready-to-use commercial soap spray. For more information see the file on Controlling Scale
Plants Stunted, Yellowed; Root Lesions Nematodes
Nematodes are not insects, but slender, unsegmented roundworms. Most are microscopic-sized soil dwellers. They have piercing-sucking mouthparts and feed on cell contents. Several kinds of nematodes occasionally attack clematis leaves or roots. Infested plants look sickly, wilted or stunted, with yellowed or bronzed leaves. They decline slowly and die. Root systems are poorly developed, even partially decayed. Control the pests by digging up and discarding damaged plants and their surrounding soil. Drench the soil with diluted fish emulsion that repels nematodes. For more information see the file on Controlling Nematodes
Stems Girdled, Foliage Dies Back due to Clematis Wilt
Clematis wilt is caused by a fungus that produces reddish lesions on the stems; causing foliage above the lesions to suddenly wither. On established plants, the older, woody stems are usually attacked first. If unchecked, the fungus moves up and down the stems, eventually killing the plant. The disease is encouraged by wet weather and thick, tangled top growth that doesn't dry out. As soon as you notice the top growth withering, cut the vine back to 6 inches above the ground (lower if there are lesions below that point). The vine usually sends up new shoots from the base. Burn the prunings or dispose of them in a trash bag. Spray healthy plants with ferbam fungicide once a week as a preventive. For more information see the file on Controlling Fungal Disease
Leaves Covered With Gray Powder means Powdery Mildew
Powdery mildews are caused by fungi that live on the surface cells of the clematis plant, not inside them. Infected leaves are covered with a white or ash-gray powdery mold. Badly infected clematis leaves become discolored and distorted, then drop off. Powdery mildews thrive in both very humid and very dry weather. Spray affected plants thoroughly with wettable sulfur once or twice at weekly intervals starting as soon as the whitish coating of the fungus appears. Collect and discard all aboveground refuse in the fall. For more information see the file on Controlling Fungal Disease
Leaves Spotted or Blotched indicates Leaf Spot
Various fungi cause leaf spots on clematis. Usually the spots are brown to black, and they may join to form large patches of dead tissue. Sometimes the spots have visible groups of fruiting bodies in them. Pick off and discard the infected leaves, and remove and discard seriously infected plants, together with the soil around them. Spray clematis vines with a flowable sulfur spray every seven to ten days until the symptoms subside. Since leaf spot fungi thrive in moist conditions, avoid wetting the foliage when watering plants. For more information see the file on Controlling Fungal Disease
Stems Gnawed Through because of Rabbits
Rabbits can be very destructive to newly planted clematis. Protect the stems with an 18-inch high strip of chicken wire embedded in the ground. Once the plants become well established, it's usually safe to remove the wire. See the file on Dealing With Rabbits
