Walnut twig beetle and thousand cankers disease. Walnut twig beetle, Pityophthorus juglandis, is a tiny bark beetle that attacks only walnut trees. The beetle has been in California for many decades but recently became associated with a new fungus, Geosmithia morbida. The fungus kills the phloem and cambium of the tree but cannot move far within the tree on its own; it is dependent on the beetle to spread it as the beetle bores into trees to feed and reproduce. The disease caused by this beetle-fungus-complex is called thousand cankers disease because it leaves hundreds of lesions on severely infested trees. The disease can kill trees within several years and many black walnuts along roadsides and riparian areas throughout
Polyphagous shot hole borer. Like the walnut twig beetle, this tiny borer, Euwallacea sp., spreads a fungal pathogen (in this case a Fusarium species) as it bores into trees. The relationship between the beetle and fungus is a symbiotic one with the beetle feeding on the fungus as it grows through the vascular system of trees. This beetle and pathogen have a broad host range and many trees have been affected including avocados, boxelder, coast live oak, liquidambar, and sycamore. Initial finds were in the Los Angeles area in 2012, but the beetle and disease have now been found as far north as Santa Cruz.
For more information on this pest, infestation zones, and ways you can help limit the spread, see the University of California Polyphagous Shot Hole Borer web site and the Center for Invasive Species Research.
[Text taken from the original article “Exotic Pests Invade California Landscapes” by Mary Louise Flint]
Keywords:
- Author: Mary Louise Flint
[From the April 2014 issue of the UC IPM Green Bulletin newsletter]
Over the last several decades dozens of exotic pests have invaded California landscapes, causing at least temporary havoc and sometimes severely affecting the aesthetic value of plants or even killing them. Giant whitefly, hackberry woolly aphid, eucalyptus red gum lerp psyllid, Diaprepes root weevil, myoporum thrips, light brown apple moth, spotted wing Drosophila, and olive fruit fly are just a few now established pests that were unknown in the state 25 years ago.
These invaders have come from all over the globe—Asia, Africa, Europe, Australia, Central and South America, and parts of North America. Many new pests arrived on nursery stock; others were imported with shipments of wood, produce, or packing material. Some pests were inadvertently brought in on vehicles or with travelers. Many safeguards including quarantine programs, border inspections, careful procedures at plant nurseries, and outreach programs to educate the public about not moving wood, plants, or produce into the state have had a significant effect in reducing the spread of invasive pests. However, despite these efforts, there is little doubt that new species will continue to arrive.
Five of the newest invaders of concern to landscapers are described in the following paragraphs. For information on these and other exotic pests see the web sites of the UC Riverside Center for Invasive Species Research, the California Department of Food and Agriculture, or the UC Statewide IPM Program.
Goldspotted oak borer. First identified in eastern San Diego County in
Polyphagous shot hole borer. Like the walnut twig beetle, this tiny
Brown Marmorated Stink Bug. A native of Asia, the brown marmorated
This article was originally published in the April 2014 issue of the UC IPM Green Bulletin. See this and other articles at http://www.ipm.ucdavis.edu/greenbulletin/index.html.