Honeysuckles are deciduous, evergreen or semievergreen vines and shrubs of the Lonicera genus. Honeysuckles boast drooping pairs or clusters of vibrant, fragrant flowers in pink, purple, red, orange, cream or yellow shades. Purple or red berries form after the flowers bloom. Honeysuckle shrubs work well as background plants or taller ground covers. Vining honeysuckle species can be trained to climb trellises. These plants are susceptible to various honeysuckle diseases.
Sooty mold (Alternaria) is a deep black fungus that forms a dark coating on the surface of honeysuckle leaves, branches and fruit. Sooty mold fungus feeds on honeydew, the clear, sticky, sweet substance secreted by honeysuckle aphids, whiteflies and mealybugs. The honeydew drops off of the insects and onto the honeysuckle plant. Wind-blown sooty mold fungal spores stick to the honeydew and begin growing. When the fungal spores germinate, they send out mycelial threads, or strands of black fungus. The black fungal strands cover plant tissue. While the sooty mold itself doesn’t kill plants, a severe mold coating can screen out sunlight and decrease the plant’s ability to make food.
Micronutrient chlorosis is a honeysuckle disease typically caused by manganese, iron or zinc deficiencies. Chlorosis first shows up in a light green or yellow discoloration on the areas between leaf veins. Chlorosis symptoms gradually worsen, causing leaves to turn pale yellow, brown along the edges and curl. Angular brown spots might also appear between the leaf veins. Chlorosis of plants in acidic soil is frequently caused by the careless disposal of lime, ashes, detergents or caustic chemicals.
Powdery mildew (Microsphaera) results in a white or gray fungal growth coating the upper surface of lower honeysuckle leaves. As this honeysuckle disease progresses, the small, circular spots expand and coalesce, which results in a continuous mat of powdery mildew. Many individuals mistake this disease for simple dust accumulation on the plant’s leaves. If this disease is left untreated, the powdery mildew fungus causes premature leaf drop and might even kill the invaded tissue. Powdery mildew symptoms usually appear in mid- to late summer following periods of high humidity.
Honeysuckle leaf blight is caused by the Insolibasidium deformans fungus. Leaf blight initially causes new honeysuckle leaves to crinkle and roll. Interveinal tissue turns brown or yellow within a few days. Some leaves appear to have brown lesions surrounded by yellow rings. As the disease ages, the affected leaves gradually curl and turn brown. Severely infected honeysuckle plants suffer premature leaf-drop. White spores may develop on lower leaves during humid, cool weather. The leaf blight fungus overwinters in leaves infected the previous year. Spring rain washes the spores to freshly formed honeysuckle leaves, where the fungus starts new infections.
Providing honeysuckle plants with the proper care is the best way to avoid honeysuckle diseases. Honeysuckles should be planted far enough apart to promote healthy air circulation. These plants should be watered at the base instead of over the flowers and leaves. Consistent deadheading of old blooms is essential as is removing any dead material at the base of the honeysuckle shrub or vine. Mildew and mold should be treated with a fungicide during the early stages. Aphids should be kept at a minimum to reduce the chances of a honeysuckle plant developing sooty mold.