Two Lined Chestnut Borer

Agrilus bilineatus

Two-lined chestnut borer, Agrilus bilineatus, is an insect pest that attacks oaks, beech, hornbeam and chestnuts that are stressed by drought, compaction or other insects or diseases. Trees can be killed in the first year of attack; however, death usually occurs after 2 to 3 successive years of infestation. Typically, the crown is attacked during the first year, while the remaining live portions of the branches and trunk are infested during the second and third years.

Download Two Lined Chestnut Borer Fact Sheet

Treatment Strategy

Understanding that two-lined chestnut borer primarily attacks stressed trees helps in designing an effective treatment program. While alleviating the stress on infested trees through watering and mulching will support the trees natural defense system, the use of insecticides is recommended to get an infestation under control. Preventative and therapeutic treatments with insecticides need to target this pest where it feeds - the conductive tissues of the tree. Soil applied systemic insecticides such as Optrol™ and Transtect™ offer additional protection from bronze birch borer by being distributed in this area.

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Two Lined Chestnut Borer Treatment Option 1

Cultural Practices

Watering

Adequate water is a key factor in maintaining healthy trees. A slow, deep watering event once every few weeks during dry conditions will help maintain soil moisture levels and minimize the stress that invites two-lined chestnut borer.

Mulching

Mulch is very beneficial for all trees because it reduces competition with turf and moderates soil temperature and moisture levels. The addition of 3 inches of wood chips or shredded bark under the drip line can have a very beneficial effect by holding in moisture and promoting healthy fibrous roots.

Fertilizing

Proper fertilization can be beneficial for any tree. However, it is important to know that research shows that too much nitrogen will increase your trees susceptibility to two-lined chestnut borer by increasing succulent growth. Do not fertilize oak trees that are showing symptoms of two-lined chestnut borer.

Application Type – Cultural Practices

DIY Equipment Needed: 

Soaker hose (for watering)

Mulch

• Rake and shovel

• Low nitrogen fertilizer

Two Lined Chestnut Borer Treatment Option 2

Preventative Treatments

Important trees that are not yet showing symptoms or those that are beginning to die back should be treated annually to prevent further symptoms or to keep insects out. Optrol™ is applied each year, preferably in the spring or fall and lasts one full year in the tree. Mid-summer applications can be done but are not optimal.

Application Type Soil Drench

DIY Equipment Needed: 

Optrol™

• Measuring or diameter tape

• Gloves

Soil Drench: bucket or watering can; shovel or trowel

Two Lined Chestnut Borer Treatment Option 3

Therapeutic Treatments

Trees that are showing symptoms in less than one third of their canopy are still good candidates for treatment. Once an infestation progresses beyond this point the conductive tissues are too compromised to get insecticides into the tree. Dead branches will not grow back and should be pruned out.

In order to effectively control a heavy two lined chestnut borer infestation, two treatments are required in the first year. The first needs to be fast acting to kill the larvae that are in the tree. Transtect is a quick absorption insecticide that effectively controls borers and will move into your tree in about a week. Following up with an Optrol™ application will provide one full year of protection. Annual Optrol™ applications will maintain this protection with no need for additional Transtect™.

Application Type – Soil Drench

DIY Equipment Needed: 

Transtect

• Measuring or diameter tape

• Gloves

• Soil Drench: bucket or watering can; shovel or trowel

Other Treatment Options

Protecting the trunk of an oak with sprayed insecticides multiple times in a season was the standard treatment in the 1990’s and before. With the advent of soil applied systemic insecticides this method is no longer necessary. If you prefer this method of treatment, please contact the Tree Geeks for more information.

Two Lined Chestnut Borer DIY Kit

Option 1

Application Type – Cultural Practices

DIY Equipment Needed: 

Soaker hose (for watering)

Mulch

• Rake and shovel

• Low nitrogen fertilizer

Option 2

Application Type Soil Drench

DIY Equipment Needed: 

Optrol™

• Measuring or diameter tape

• Gloves

• Soil Drench: bucket or watering can; shovel or trowel

Option 3

Application Type – Soil Drench

DIY Equipment Needed: 

Transtect

• Measuring or diameter tape

• Gloves

• Soil Drench: bucket or watering can; shovel or trowel

How Is It Spread?

Just like most wood boring beetles, it is the larval stage of twolined chestnut borer that causes injury to the tree. The larvae feed on the sapwood, disrupting the flow of water, nutrients and sugar. Eggs are laid in the late spring, hatching and beginning to feed throughout the summer.

Susceptible Trees

Although twolined chestnut borer is a primary pest of oak and chestnut trees, there is some evidence to suggest that it will also attack beech and hornbeam as well. The most commonly affected oaks include chestnut, white oak, black oak, red oak, scarlet and bur oak.

Symptoms

• Sparse, small and discolored foliage, which is followed by the dieback of branches.

• Leaves of infested branches turn uniformly redbrown and remain attached to the tree. The leaves on non-infested branches remain green. Infested oaks have a distinct pattern of dead and live leaves on them.

• D-shaped exit holes.

• Meandering feeding galleries underneath the bark.

Lookalikes

Oak wilt, drought stress, construction damage

Related/Similar Problems

Oak wilt, drought stress, construction damage

Timing

Spring or fall

Urgency

High

Risk of Spreading

Moderate

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