Lilac borers of Lilac

Disease Information

Lilac borers


These are very niggling pests that are actually the larvae of a wasp-like moth called Podosesiasyringae var. syringae, whose wings are semi-transparent and brownish. This pest lays large amounts of eggs in late spring. They usually lay their eggs on the stems of lilac shrubs and ash plants.

Symptoms and damage

While they are hatching, the larvae penetrate the branches and are nourished by the wood. Initially, these pests remain out of sight and one notices their presence for the first time when they find the entire leaves on a branch or stem turning yellow and wilting. This usually happens during the spring or towards the beginning of summer. Infestation by lilac borers may cause the bigger branches to become distended and eventually break.
If you take a closer look at such branches, you will notice tiny holes measuring roughly about the size of a pencil lead in diameter at a level of one or two feet (30 cm to 60 cm) higher than the ground. Just below it, you will notice some sawdust. In fact, these holes are actually exit paths of lilac borers and they suggest that the pests have already left, but still some others may be at work. These pests are very visible when you are pruning the plants. In fact, you may even find the borer tunnels breaking through the heartwood, especially of the older branches.

Treatment for tree borers can be difficult if adults are already present and laying eggs throughout the tree. Trees with many holes bored through the trunk are often easier to replace than to successfully treat, since the internal damage can be extensive after just a few seasons. Prevention is key if your trees are unaffected, but tree borer insects are active nearby.

Trees that are not infested, or have only a few noticeable holes, may be protected from borers by improving care. It may seem too easy, but borers are attracted to trees that are stressed and injured; pruning wounds are a common entry point for the first generation of invading borers.

Adding mulch around your tree and providing it with supplemental water and fertilizer will help it fight off borers and heal from previous damage.

Chemical Control

Trees that are riddled with borer holes are past the point of saving. These trees must be removed for safety`s sake; galleries can extend several inches past the penetration point, weakening limbs and branches that may snap with the first strong gust of wind. You must burn or otherwise destroy the infected tree`s tissues as soon as possible to prevent any borers that remain from escaping to nearby trees.

Chemical treatments are available for trees with minor infestations, though they generally are aimed at preventing re-infestation. Residual insecticides like carbaryl, chlorpyrifos, lindane and permethrin are designed to remain on tissues for many weeks, so that any insect that comes in contact with them will die immediately. All woody surfaces must be covered for these materials to work.

Imidacloprid and dinotefuran, systemic insecticides, can control borers that remain close to the bark layer of the tree, but should not be applied without identifying the pest inside your tree first. Sticky traps or pheromone-baited traps can be helpful in this department, but don`t rely on these traps to provide control for your borer problem.




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