vigil for plant ailments: common shrub pests and afflictions to monitor closely
Shrubs are a beloved addition to many gardens, but they can fall victim to various pests and diseases. Here's a guide to some common issues and effective management strategies.
Pests
Azalea Lace Bug
Symptoms of an Azalea Lace Bug infestation include yellowing leaves and the presence of sooty mold on leaves. To treat this pest, consider removing and replacing heavily infested shrubs with resistant varieties. Alternatively, use horticultural oils or soaps with full coverage, being mindful to avoid systemic insecticides near pollinators.
Japanese Beetles
Japanese Beetles can be identified by the chewed leaves and flowers they leave behind. Hand-picking beetles is an effective method of control, or in severe cases, the use of traps or row covers may be necessary.
Diseases
Leaf Spot
Leaf Spot is characterised by brown or black spots on leaves. To manage this disease, prune and remove infected leaves, using sterile tools to prevent spread. Improving air circulation and reducing moisture can also help.
Root Rot
Root Rot is identified by soft, mushy roots. To treat this, improve drainage, remove infected roots, and consider using fungicides if necessary.
Integrated Pest Management (IPM) Strategies
An effective approach to managing pests and diseases in shrubs is the use of Integrated Pest Management (IPM) strategies. These include early detection, proper plant selection, biological control, chemical control when necessary, and companion planting.
- Early Detection: Regularly monitor shrubs for signs of pests or diseases.
- Proper Plant Selection: Choose resistant varieties.
- Biological Control: Use natural predators to control pests.
- Chemical Control: Apply targeted chemicals only when necessary, considering environmental impact.
- Companion Planting: Plant beneficial species alongside shrubs to deter pests.
Environmental Considerations
- Minimise Chemical Use: Use pesticides judiciously to avoid harming beneficial insects.
- Protect Pollinators: Avoid using systemic insecticides when pollinators are present.
- Environmental Sensitivity: Always follow label instructions for treatments.
Additional Information
- Volutella blight and boxwood blight can affect the same boxwood shrub in the same year.
- Bagworms are a common shrub pest that affect juniper, arborvitae, and other shrubs.
- Japanese beetles are difficult to eradicate due to their flying nature, but their grub larvae can be controlled with low-risk insecticides.
- Boxwood blight symptoms include brown spots on leaves, followed by a rapid defoliation. Leaves generally grow back and give you a chance to prevent a recurrence. Remove all the fallen debris to the trash and practice good sanitation and aeration.
- Shrub pests and diseases are common problems among landscape plants.
- Borers affect lilacs, viburnums, and dogwoods, for example, by boring into twigs and branches. Control this by pruning off infected branches.
- Leafminers affect azaleas, boxwoods, conifers, and hollies by mining into the leaves. Damage shows meandering tunnels or blistering. Remove affected leaves to the trash.
- Spider mites populations can increase rapidly and are identified by webbing and mottled foliage, especially during hot, dry weather. Severe feeding can kill the plant. Treat with forceful sprays of water, insecticidal soap, or horticultural oils.
- Aphids feed on leaves and stems and are common on most plants, but generally do not need treatment unless the infestation is severe. Effective treatments include a blast of water, insecticidal soap, or Neem oil.
- Powdery mildew fungus is common on crape myrtles, lilacs, roses, dogwood shrubs and more. Affected leaves have a whitish appearance as if sprinkled with powder. Leaves brown and drop off. Prevention is the best medicine with good cultural practices and full sun. Particularly susceptible plants, such as crape myrtles, may benefit from a preventative fungicide.
- Scale, both soft scale and armored scale, can be damaging to shrubs such as azalea, camelia, holly, and euonymus. They often go unnoticed until they have increased in number. Insecticidal soaps or horticultural oils can be effective, but the timing must be right to target the crawler stage.
- Root rot fungi affect shrubs that are overwatered or drain poorly. Prevent root rot with well draining soil and letting plants dry out between waterings.
- Volutella blight grows on infected shoots from the previous fall on boxwoods. Leaves eventually turn yellow or tan and remain on the shrub for an extended period. Prune off dead branches and spray the plant with a copper fungicide if the infection is severe. Provide good sanitation and aeration.
- Leaf spot diseases are common on many shrubs and can be fungal or bacterial. Good sanitation is important, such as removing all the fallen leaves to the trash. Avoid watering overhead.
- Anthracnose is prompted by cool, wet weather and causes sunken spots on leaves, twigs, or fruits. Pick up fallen leaves or other affected plant parts in fall to help prevent its recurrence.
- Black spot fungus is common on roses and can cause complete defoliation of the plant. Fungicides are best applied as a preventative measure. Pick up and destroy any leaves that fall.
- Lace bug feeding can discolor leaves, but natural predators such as lady beetles and assassin bugs can help control them.
- Botrytis blight affects flower buds, often preventing them from opening, and can spread to other plant parts. Roses, hydrangeas, and blueberries often are affected. Wet, humid weather brings it on and hot, dry weather can stabilize it. Clean up fallen debris in the fall and make sure the plant has good air circulation. Next year, use a fungicide to prevent a recurrence.
- Sooty mold is a fungal disease that grows on honeydew-affected plants, and is secreted by aphids, scale, whiteflies and other sap-sucking insects. Wash the mold off with water or soapy water and treat the insect that is producing the honeydew.
- Verticillium wilt fungi live in the soil and invade a plant's vascular system, causing yellowing, wilting, and curling leaves. Remove and discard the plant in the trash.
- Caterpillars, such as sawfly, moth, and butterfly larvae, generally don't do enough damage to warrant control.
- Rose rosette is a virus transmitted by the eriophyid mite. Symptoms include leaf proliferation, witches broom, thorniness, and red coloring. There is no remedy; roses should be removed and destroyed.
- Common shrub diseases include root rot and leaf spot.
- Black vine weevils target rhododendron, yew, hemlock, azalea, and mountain laurel shrubs.
- Viruses infect a plant's cells, interfering with cell functions. Woody ornamentals can overcome viruses so replacement is not usually needed.
- Rust fungus is common and is host-specific. Eliminate overhead watering and practice sanitation. Remove fallen, infected leaves or fruit and dispose of them in the trash.
- Fire blight is a bacterial disease transmitted through rain, splashing water, and insects. Infected cankers ooze and leaves and blossoms take on a burned appearance. There is no cure so pruning out the infected branches is necessary.
- Prevention is always the best course of action for managing shrubs.
- Aphids, scale, spider mites, and Japanese beetles are common shrub pests that are not host-specific.
Maintaining a home-and-garden lifestyle often involves gardening and taking care of shrubs, which can be vulnerable to various pests and diseases like Azalea Lace Bug, Japanese Beetles, Leaf Spot, Root Rot, Volutella blight, boxwood blight, and more. To manage these issues, consider using Integrated Pest Management (IPM) strategies, such as early detection, proper plant selection, biological control, chemical control when necessary, and companion planting. These methods can help in minimizing chemical use, protecting pollinators, and promoting environmentally sensitive treatments. In case of severe infestations or diseases, specific management strategies, such as pruning, using horticultural oils, or fungicides, may be necessary.
