|Do You Feel Lucky?|
|Driving over a downed eucalyptus branch can lead to this|
Drought. Psyllids. Borers. Whiteflies. Caterpillars. Root rot. Improper pruning. Sudden Limb Drop. As if the local eucalyptus trees don't have enough problems. Now entering Northern California is another pest problem for this widely planted tree, the eucalyptus tortoise beetle, first discovered in Riverside County seven years ago.
There are those who would have you remove eucalyptus trees, especially the blue gum (E. globulus) and red gum (E. camuldensis) due to their invasiveness. Eucalyptus trees can be messy, susceptible to wind damage and tough to plant anything else beneath them. Eucalyptus trees have their place in California, especially rural areas where their fast growing, evergreen qualities can serve well to prevent soil erosion as a windbreak. In urban areas, tall eucalyptus trees are more problematic. There are better choices for backyard trees in cities and suburbs.
While the red gum lerp psyllids are sucking away along the undersides of eucalyptus leaves and the longhorned eucalyptus borer is tunneling its way into the tree's branches and trunk, the eucalyptus tortoise beetle is chewing semicircular or irregular notches along the leaf margins, leaving only the mid-vein when its done dining.
|Eucalyptus long horned beetle|
|eucalyptus tortoise beetle|
|red gum lerp psyllids on E. camuldensis|
|The psyllid is inside the lerp, well protected|
Although beneficial insects have been introduced to battle the red gum lerp psyllid, eucalyptus long-horned borer and the eucalyptus tortoise beetle, it may be years before the beneficials population is large enough to control these pests. In the meantime, homeowners can help out their suffering eucalyptus trees with a few simple steps:
* Water eucalyptus trees, once a month, during the summer. Soak the area beneath the outer canopy of the tree. Don't flood the area near the trunk, though; eucalyptus are susceptible to root rots. Drip and soaker hoses are preferable to sprinklers.
* Don't fertilize these trees. Nitrogen-induced tender, new growth is especially susceptible to these pests.
* Clean up any dead branches on the ground, remove dead trees. This could be a breeding area, especially for the eucalyptus longhorned beetle.
* Prune in December or January to avoid borer attacks to freshly cut limbs.
* Don't plant pest-susceptible eucalyptus species. The varieties most susceptible to damage by these critters include the blue gum (Eucalyptus globulus), manna (E. viminalis) and the widely planted river red, E. camaldulensis.
* Choose eucalyptus varieties that have shown some resistance to these pests. This list would include the Australian beech (E. polanthemos), silver dollar eucalyptus (E. cinerea), gray ironbark (E. paniculata), the narrow-leaved eucalyptus (E. spathulata), and the hybrid E. trabutii. Several more are listed here.
* Read and follow all label directions if using a soil drench systemic insecticide whose active ingredient is imidacloprid, which may control the red gum lerp psyllid; studies aren't in yet if it is effective on the tortoise beetle. The University of California reports mixed results on the efficiency of imidacloprid in controlling the red gum lerp psyllid; for best results apply this soil drench in early spring.
* According to the UC Davis Integrated Pest Management Project, limit any chemical treatments to situations where damage is intolerable or pests threaten tree survival. Most pesticides are at least somewhat harmful to beneficial predators or parasites. Imidacloprid applied to flowering plants or the soil beneath them may move to nectar and poison the nectar-feeding adult parasites, which during their larval stage partially or completely control other pests. Be aware that imidacloprid application may contribute to outbreaks of spider mites and other pests.
Use pesticides rarely and always as a last resort. Most tortoise beetle infestations do not require pesticide treatments, and pesticides disrupt biological control of other pests.
For more Information:
The Eucalyptus Tortoise Beetle:
Red Gum Lerp Psyllids:
Eucalyptus Longhorned Borers:
The most diverse collection of eucalyptus trees in North America is at the UC Santa Cruz Arboretum. Plan a visit!