Dogwood Borer

The Dogwood Borer is a species of clearwing moth scientifically known as Synanthedon scitula. This insect is one of the most destructive pests of flowering dogwoods and can weaken or even kill the host plant.

Host Plants

The Dogwood Borer primarily targets various species of dogwood trees (Cornus spp.) as its host plants. However, it is not restricted solely to dogwoods. It has been known to infest other types of trees as well, including:

• Apple trees (Malus spp.)
• Pecan trees (Carya illinoinensis)
• Hawthorn trees (Crataegus spp.)
• Mountain Ash trees (Sorbus spp.)
• Flowering Cherry trees (Prunus)
• Chestnut trees (Castanea spp.)
• Hickory trees (Carya spp.)
• Willow trees (Salix spp.)
• Birch trees (Betula spp.)
• Oak trees (Quercus spp.)
• Pine trees (Pinus ssp.)
• Elm trees (Ulmus spps.)

Regions impacted

Dogwood borers are prevalent primarily in eastern North America.

Description

The Dogwood Borer is a clear-winged moth that resembles a wasp and has a wingspan of about 1/2 inch (1 cm). Its body is predominantly dark blue or black, accented by yellow bands.

The larvae are cream-colored with a brown head and can grow up to a 1/2 inch long (1 cm).

Life Cycle

The life cycle of the Dogwood Borer consists of four stages: egg, larva, pupa, and adult. Understanding the life cycle is essential for effectively managing and controlling this pest. Here’s an overview:

• Egg Stage: Adult female moths lay eggs on the bark of host trees, particularly in crevices, wounds, or areas where the bark is damaged. The eggs are tiny and difficult to spot with the naked eye.
• Larval Stage: Once the eggs hatch, the larvae bore into the tree to feed on its tissue. This is the most damaging stage, as the larvae create tunnels in the wood that disrupt nutrient and water flow.
• Pupal Stage: After feeding for several weeks or months, depending on environmental conditions, the larvae form a pupa, usually within the same tunnels they’ve created in the tree. The pupal stage can last a few weeks.
• Adult Stage: Adult moths emerge from the pupae, usually in late spring to early summer. They are active for about a month, during which they mate and lay eggs to start the next generation.

The entire life cycle can last from one year to two years, depending on environmental conditions. It’s critical to target management efforts, particularly insecticide applications, to the most vulnerable stages of the borer’s life cycle, typically the larval stage.

Damage and Detection

Damage

The Dogwood Borer primarily targets the vascular system of the host tree, causing extensive internal damage that may not be immediately visible. The larvae create tunnels, known as galleries, within the bark, disrupting the flow of nutrients and water. This weakens the tree, making it more susceptible to other diseases and environmental stress. Signs of damage can include:

• Wilting and dying branches
• Sloughing or shedding of loose bark
• Poor overall tree health
• Reduced flower and fruit production
• Crown dieback
• Exudation of sap or resin around the base or on the trunk
• Formation of “borer holes” or small openings on the bark
• Visible frass (excrement) around affected areas

Detection

Accurate detection is crucial for effective management. Here are some ways to detect Dogwood Borer infestations:

• Visual Inspection: Look for visible symptoms like wilting leaves, dying branches, and small holes in the bark. Also, check for sawdust-like frass around these areas.
• Sap Flow: An unusual flow of sap from the trunk or branches can be a sign of borer activity.
• Traps: Pheromone traps can be used to capture adult moths, providing an indication of the level of infestation. However, the presence of moths doesn’t necessarily confirm damage, as they could be from neighboring areas.
• Tree Health: Unexplained declines in tree health, such as leaf drop, reduced fruiting, or poor growth, can be indicative of a borer issue, among other potential problems.
• Physical Examination: In severe cases, you may need to carefully remove a small section of bark to inspect for larvae or tunneling, though this is generally not recommended as it can further stress the tree.
• Professional Help: If you suspect an infestation but aren’t sure, consulting an arborist or other tree health professional is advisable for accurate diagnosis and treatment recommendations.

Early detection is crucial for successful control and prevention of further damage. If left unchecked, a severe infestation can lead to the decline and eventually the death of the host tree.

Prevention and Control

Effective management of Dogwood Borer infestations involves both preventative measures and active control methods.

Prevention:

• Tree Health: Keeping the tree healthy and stress-free can make it less attractive to borers. Regular watering, fertilization, and proper pruning practices can go a long way.
• Mulching: Proper mulching around the base can protect the tree from mechanical injuries that are entry points for borers.
• Tree Wraps: Wrapping the lower trunk can deter females from laying eggs. However, this may not always be effective and is generally more useful for young trees.
• Inspection: Regularly inspect the trees for early signs of infestation. Catching the problem early makes control easier and more effective.
• Pheromone Traps: These can be used as a monitoring tool to detect the presence of adult borers.

Control:

• Chemical Control: There are various insecticides available that can be effective against Dogwood Borers, including trunk injections and topical sprays. Always read and follow label directions, and consult local regulations.
• Pruning: Cutting away dead or severely infested branches can limit the spread of the borer, but it should be done carefully to avoid creating new entry points for the larvae. Prune in late winter (when the moths are not active).
• Cutting Out Borers with a Sharp Knife: This method involves carefully cutting away the infested portion of bark to expose the borer tunnels and larvae. Once exposed, the larvae can be removed and destroyed. This method is most effective when only a few borers are present, and the infestation is localized. However, this method comes with some risks (damage to tree, incomplete removal, infection risk).
• Crushing Borers with Wire: This involves inserting a flexible yet sturdy wire into the borer tunnels to physically crush the larvae. This method is less invasive as it doesn’t require cutting into the tree. However, it also has limitations ( incomplete removal, and potential damage to the tree’s internal tissues).
• Replacement: In extreme cases where the tree cannot be saved, replacing it with a more borer-resistant species might be the best long-term solution.
• Quarantine: Newly purchased trees should be inspected for signs of borer activity to avoid introducing an infestation.
• Timely Action: The sooner you act, the better the chances of controlling the infestation effectively.
• Professional Help: For large or advanced infestations, consult a certified arborist for specialized treatments, which may include systemic insecticides.

By employing a combination of these preventative and control measures, you can significantly reduce the risks associated with Dogwood Borer infestations.