Arborvitae are popular landscape plants, valued for their dense, evergreen foliage and ability to form privacy screens. While generally robust, these plants can become susceptible to certain common insect pests. This guide helps in identifying and managing such pest problems.
Common Arborvitae Pests
Several types of insects commonly target arborvitae, each with distinct characteristics and feeding habits. Spider mites, tiny arachnids, are often yellowish, greenish, or reddish and use piercing-sucking mouthparts to extract cell contents from needles, leading to a speckled appearance on the foliage.
Bagworms are caterpillars that construct spindle-shaped bags from silk and bits of the host plant’s foliage, making them camouflaged against the branches. These larvae feed voraciously on arborvitae leaves and twigs, causing significant defoliation. Arborvitae leafminers are small, greenish larvae that tunnel within the narrow leaflets of the plant.
Scale insects, such as the Fletcher scale, are sap-feeding pests that appear as small, often hemispherical, bumps on stems and needles. Aphids, like the arborvitae aphid, are soft-bodied, pear-shaped insects that gather in colonies to suck sap from stems, leaves, and buds.
Recognizing Infestation Signs
Specific changes in your arborvitae can indicate a pest infestation. Browning or yellowing foliage is a common symptom, which can result from sap-feeding pests like spider mites or scale insects. Spider mites, in particular, cause a fine yellowish speckling or bronzing on the foliage, and in severe cases, fine webbing may be visible between needles or branches.
Chewed or skeletonized leaves and defoliation are strong indicators of pests like bagworms, which consume needles and small branches. The most distinctive sign of bagworm activity is the presence of characteristic two-inch-long silk bags hanging from branches, often incorporating bits of the plant’s foliage. Stunted growth can also occur when pests draw nutrients from the plant.
Sticky honeydew is excreted by sap-sucking insects like aphids and scale. This sugary substance can lead to sooty mold, which appears as a black, powdery coating on the foliage. Brown tips on branches, especially in late winter or early spring, can sometimes be a sign of arborvitae leafminers, which cause foliage to turn yellow then brown from the tips downward.
Treating Arborvitae Bugs
Addressing arborvitae pest issues involves an integrated pest management (IPM) approach, combining various strategies to minimize pest impact. For bagworms, manual removal is an effective option for smaller infestations, where the silk bags can be hand-picked or cut from the branches before the eggs hatch in late spring.
Strong water sprays can dislodge soft-bodied pests like aphids and spider mites from the foliage. Horticultural oils and insecticidal soaps are general treatments for many soft-bodied pests, including aphids, spider mites, and scale, by suffocating them or disrupting their cell membranes. These should be applied thoroughly, ensuring direct contact with the pests.
When infestations are severe, targeted chemical insecticides may be necessary. Always follow label directions carefully for proper dosage and safety precautions. Encouraging beneficial insects, such as ladybird beetles and predatory mites, can also help manage pest populations naturally, as these insects prey on common arborvitae pests.
Preventing Future Infestations
Proactive measures and proper cultural practices contribute significantly to the long-term health of arborvitae, making them less susceptible to pest problems. Proper planting is foundational; arborvitae thrive in full sun to partial shade and prefer well-drained, slightly acidic to neutral soil. Adequate spacing between plants ensures good air circulation, which helps deter some pests and diseases.
Consistent and adequate watering is important, particularly during dry periods, to prevent drought stress that can weaken plants and make them more vulnerable to infestations. However, overwatering should be avoided, as constantly soggy soil can lead to root issues. Applying mulch around the base of the plants helps retain soil moisture, regulate soil temperature, and suppress weeds.
Regular pruning to remove dead, diseased, or overcrowded branches improves air circulation and plant vigor. This practice also allows for routine inspection of the plants, enabling early detection of any pest activity before it escalates. Choosing pest-resistant arborvitae varieties can further reduce the likelihood of future pest issues.