What are the white spots on eucalyptus tree leaves?

Answer 1

I researched this question, as I have this problem around my own house. According to another web site, http://www.buginfo.com/article.cfm?id=64:

= Lerp Psyllids on Eucalyptus Trees = In a trend that sees no stopping, the 1990's brought many new pests to the United States, and several of these have surfaced in California. The eucalyptus trees encompass many species of hardy, evergreen trees that are native to Australia. They thrive in the moderate climate in much of California, and for many years had virtually no pests attacking them. Now, however, there are several species of insects causing problems for these trees, and one group is the "psyllids", also called Jumping Plant Lice. These insects are related to aphids, but are more mobile in the adult stage and do not have the two little pointed horns at the end of the abdomen, called "cornicles", that aphids have. In 1991 the "Blue Gum Psyllid" was discovered in the Monterey area along the coast, and in 1998 the "Red Gum Lerp Psyllid" showed up in the Los Angeles area. In both cases these foliar pests spread very, very rapidly throughout the state. Now, this is a pretty unusual name for a bug - a "lerp" - so what exactly does that mean. Well, Lerp refers to the early stage of the bug, and the little white capsule that it creates over itself on the leaf. These insects feed by inserting their mouth, a sucking straw, into the leaf, and sucking out liquids from the leaf. Much of this liquid is sugary, and the psyllid nymphs pass the liquid through their system, excreting a sticky substance called "honeydew" out their back ends. We see this same honeydew from aphids, as it coats sidewalks or the tops of our cars with a thin layer of sticky material. The word "lerp" actually has its origin as an Aborigine word that described these little structures. However, with the Lerp Psyllid the honeydew forms a crystalline shell over the bug, and eucalyptus leaves can virtually be covered with the lerps, dozens of them on every leaf on the tree. As many as eight species of eucalyptus trees are known to be attacked by this pest, but it is the Red Gum Eucalyptus - Eucalyptus camaldulensis - that seems to suffer most. Intensive infestations of the psyllid have resulted in extensive drop of leaves, branch dieback, and even death of some trees already under stress.

Answer 2

The white spots on eucalyptus tree leaves could be caused by powdery mildew, a fungal disease that thrives in warm and humid conditions. It can weaken the tree if left untreated, so it's recommended to address the issue by improving air circulation around the tree and applying fungicidal treatments if needed.