Shrub Disease Treatment

Shrub disease protection begins with a comprehensive inspection of your landscape by one of our ISA certified arborists.

During this inspection, your arborist will be able to determine the overall health of the landscape and, if necessary, diagnose any disease or insect issues so that they can recommend treatment.

Here are some of the most common diseases and insects we find on shrubs and ornamentals.

Common Diseases on Shrubs

boxwood blight dead leaves

Boxwood blight

Boxwood blight is caused by the fungus, Cylindricladium pseduonaviculatum. This disease causes lesions on the leaves, with lesions on stems following soon after. If not treated, the infection will cause the plant to drop its leaves, causing stress and eventual death.

Fire blight is caused by the bacteria Erwinia amylovora. Over 130 members of the Rosaceae family are susceptible, including; apple and crabapple, cotoneaster, firethorn, hawthorn, mountain ash, and pear.

Infected leaves, stems, twigs and fruits will turn brown to black. Fire blight will blacken the smooth-barked, green branches and leaves. Affected twigs develop a “shepherd’s crook”.

Needle, tip, or twig blights occur on many species of shrubs including arborvitae, cypress, and juniper. They start by turning the tips of twigs and ends of needles brown or grey. Black, pimple-like fungal fruiting structures may develop on needle surfaces.

These blights can be caused by fungi in the genera Phompsis, Diplodia or Coryneum.

Leaf Spot causes small, irregular brown to black spots to appear on leaves, which will eventually drop prematurely. Lesions caused by Colletotrichum gloeosporioides are round, brown spots visible on both upper and lower surfaces of leaves. These fungal diseases may first appear as symptoms of winter desiccation.

Powdery Mildew is a common fungal disease that creates a white, powdery appearance on leaves, stems, and buds. Infection often leads to leaf yellowing, premature leaf-drop, and slow growth.

Pachysandra volutella blight targets Japanese pachysandra. The stems of an infected plant will darken and die. If conditions are particularly wet,  orange/pink fungal spores will colonize the surface of dead stems. Brown and tan spots will develop on the leaves and eventually spread over the entire leaf. Concentric line patterns may be visible.

Common Pests in Shrubs

Boxwood psyllid is capable of infesting all species of ornamental boxwood. These insects overwinter by laying orangish eggs in between bud scales. Nymphs hatch early in the season and a white, waxy substance they secrete may cover the plant and be detrimental to its health. Psyllids suck sap from buds and young leaves, resulting in a cupping of new foliage.

Scale insects come in many varieties and can attack a wide range of shrubs, feeding on plant juices. They typically appear as immobile bumps. In most cases, you won’t be able to see legs or other body parts. Some species excrete a sticky substance called honeydew, which attracts other insects and mold.

Lace bug damage

Lace bug damage

Leafminers cause damage by tunneling into foliage and feeding on plant material. Over time, infestations can cause premature leaf-drop or dieback. Species that may affect your shrubs include, boxwood leafminers, holly leafminers, and arborvitae leafminers.

Spider mites are common pests with a wide range of targets, including fruit trees, vines, berries, vegetables and ornamental shrubs. Spider mites hatch out early in the growing season but remain active for a long time. Damage from spider mites appears as yellowed stippling on foliage. You may also notice fine webbing on plants.

Lace bug insects affect susceptible evergreen species such as rhododendrons, azaleas and Andromeda. Damage from previous seasons will appear as yellow stippling on leaves and dark fecal spots on the undersides of leaves. If lace bugs were present the preceding season, they may become an issue again.

Borers are a class of insect that bore into the woody parts of the plant, pushing out sawdust (or “frass”) and weakening your shrubs and ornamentals. Over time, they cause dieback and decline. Varieties that can affect your shrubs and ornamentals include dogwood borers, peach tree borers. rhododendron borers, and lilac borers.

Need an expert opinion on your shrubs? Get in touch to schedule a consultation with a certified arborist.

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