With more than 180 species of honeysuckle currently available to the landscaper, it is quite possible to encounter a diseased honeysuckle shrub while gardening. Common problems are powdery mildew, aphid infestations that cause entire branches to die back and also spider mites that discolor the shrubs' foliage with red or yellow dots. Perhaps the most serious diseases are fungal infections that affect the undersides of leaves and the soft tissues beneath the bark.
Check the honeysuckle's newest growth for leaf blight. Notice leaves that roll up or crinkle; landscapers should also check the ground around a shrub for yellowed leaves that dropped to the ground. On the leaves' undersides there is likely a fine white powder: leaf blight. This fungal infection attacks new leaves but eventually also spreads to the mature portions of the foliage.
When honeysuckle branches show discolored bumps, they likely fell victim to another fungal--or sometimes bacterial--infection: canker. Cankers form in branch tissues below the bark; when grown beyond the branches' ability to contain them, they split open and ooze a sticky sap.
Prune branch segments that hold severely diseased leaves or show cankers. Cut well below the cankers and take care not to rupture them. Remove dead leaves promptly and also rake up any leaves under the honeysuckle shrub. This curtails the spread and growth of the fungal spores or bacteria. Depending on the severity of the fungal infection, landscapers may need to apply fungicides to the undersides of the leaves to prevent further leaf blight.
Leaf Blight Expert Insight
Even as leaf blight is likely going to be a recurring problem in areas with higher moisture and the environmental presence of fungus spores, there are some honeysuckle varieties that show resistance to leaf blight. Dr. J.E. Partridge from the University of Nebraska's Department of Plant Pathology advises that wild honeysuckle (Lonicera dioica) and Japanese honeysuckle (Lonicera japonica) actually show a resistance to leaf blight, which makes them a good choice for landscapers living in highly affected areas.
Diseased honeysuckle requires careful monitoring and aggressive pruning. Another good idea is relocating the shrubs to areas where more airflow reduces the risk of moisture buildup on leaves and branches. Prune back the bottom of the shrub to decrease the problem of fungal infections from moist soil. Raking up fallen leaves decreases the spread of fungal spores to healthy leaves. Disinfect pruning shears frequently to reduce the risk of infecting healthy branches with canker-causing spores or transmitting leaf blight spores to healthy leaves.