Lemon Tree Borer - How to Identify Insect, Damage and Control Strategies

The lemon tree borer is a serious pest of citrus trees, particularly lemons and mandarins. It attacks the trunk and branches of trees, causing severe damage and potentially killing the tree. In the photo above you can see the dust created by the borer as it destroys a Tahitian Lime.

Description of Beetle

Adult beetles are brown, 1.5-3cm long, slender, elongated and with long antennae. They are active during the warmer months (October to April). The beetles lay eggs on the bark of trees on or around cracks, ragged pruning cuts and broken branches. The larvae hatch and feed on the wood for several months causing channels that can weaken and kill the tree. They are active from spring to autumn, with peak activity in summer. The larvae are white to cream-colored and can grow up to 25 mm long. They have a strong mandible and resemble a huhu grub.

Photo: Lemon Tree Borer Image By Desmond W. Helmore - Manaaki Whenua - Landcare Research, CC BY 4.0, https://commons.wikimedia.org/w/index.php?curid=72865501

Damage Symptoms

• Boring Holes: Small, round exit holes in the bark signify adult emergence.
• Wood Frass: Sawdust-like material may accumulate at the base of the tree, indicating larval activity.
• Cracked or Weak Bark: Infested areas may exhibit cracks or a weakened structure.
• Declining Health: Trees may show signs of stress, such as wilting leaves, yellowing foliage, dieback of branches and eventually the death of the tree.

Control strategies

• Ensure trees are healthy through regular watering, fertilisation, and mulching. Healthy trees are less susceptible to pests.
• Prune citrus trees when the adult lemon tree borer is not active, (June-September).
• Monitoring: Regularly inspect trees for signs of damage, such as wilting leaves, yellowing, dieback, or sawdust. '
• Remove infested branches, making sure you cut below the damaged area. Burn all prunings to stop reinfection.
• Plant Location: Avoid planting citrus trees in areas known to have a history of borer problems, if possible.
• Spraying pesticides will not control lemon tree borer as the eggs and larvae are protected by the bark.
• Natural Predators: Encourage beneficial insects and natural predators like parasitic wasps that can help control borer populations.

 

 

Photo Above:  Parasitic Wasp. Image by Pseudopanax at English Wikipedia - Own work, Public Domain, https://commons.wikimedia.org/w/index.php?curid=32088736

Regular monitoring and early intervention are key to successful management.

Photo Above: Shows a Tahitian Lime Tree that is being destroyed by Citrus Borer. Unfortunately, it was pruned in October 2022, rather than late winter early spring when it is safe to prune.