Answer: Eucalyptus trees, once thought to be virtually pest-free, are now plagued by a growing number of serious new insect pests. Eucalyptus trees have thrived in California since their introduction from Australia more than a 130 years ago. The first sign of trouble came in 1984, when the eucalyptus longhorned borer (ELB), a native of Australia, was found killing eucalyptus trees in Southern California. This beetle, which has caused much widespread damage, is now found throughout much of California. More recently, another Australian borer, commonly known as the "yellow phoracantha has joined it. While ELB prefers the trunk for ovipositing, this new borer prefers the larger branches. Together they are a destructive duo. A serious defoliating pest, the eucalyptus snout beetle, was detected on blue gums in Ventura County in 1995. Since then at least five other sap-feeding psyllids, a gall-forming wasp and another leaf-feeding beetle have been found - all of which are native to Australia. In their native habitat, none are considered to be serious pests. Their populations are for the most part, kept in check by their natural enemies. In California, however, they have been introduced without their natural control agents, thus, population buildup and spread have been rapid.
Until natural control has been achieved, the best option to manage these new eucalyptus pests is to enhance tree health by reducing environmental stress and improving growing conditions and tree care practices. Stress resulting from unfavorable environmental conditions, site disturbance, excessive or substandard pruning, excessive fertilization, soil compaction, root-loss and injury impairs health, increasing susceptibility to pests. Healthy, well-maintained trees typically have fewer pest problems. Even the healthiest trees are occasionally subject to certain pests. The point is that proper tree care promotes health while ensuring resistance to most pests and increasing tolerance to pest injury. A comprehensive tree health program should include: proper pruning, regular and thorough irrigation, mulching, judicious fertilization, and protection from injury and site disturbance.
You may want to contact your local Cooperative Extension office for additional information about the control of the pests.
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