[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 http://cisr.ucr.edu, the California Department of Food and Agriculture http://www.cdfa.ca.gov/invasives/, or the UC Statewide IPM Program http://www.ipm.ucdavis.edu/EXOTIC/index.html.
Goldspotted oak borer. First identified in eastern San Diego County in
2004, the goldspotted oak borer, Agrilus auroguttatus, has killed over 25,000 California native red oaks since its arrival and has now been detected in Riverside County. Larvae feed deep within the phloem, and adults are rarely seen. Infestations are recognized by the presence of D-shaped exit holes on trees, often accompanied by bark staining and crown decline. There are currently no good ways to manage the pest in moderate to severely infested trees. Contact your agricultural commissioner if you find infestations outside the known infested area. More information is available at http://www.ipm.ucdavis.edu/PMG/PESTNOTES/pn74163.html.
D-shaped holes on California native red oaks are a clue to goldspotted oak borer infestation.
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 California have died. No effective management tools are available. More information is available at http://www.ipm.ucdavis.edu/PMG/menu.thousandcankers.html.
Black walnut in decline due to thousand cankers disease.
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
Lesions on a live oak caused by the polyphagous shot hole borer-Fusarium complex.
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. More information is available at http://cisr.ucr.edu/polyphagous_shot_hole_borer.html.
Polyphagous shot hole borer.
Brown Marmorated Stink Bug. A native of Asia, the brown marmorated
stink bug, Halyomorpha halys, immigrated into the United States in the 1990s but has only recently been reported in California. The bug prefers to feed on seeds and fruits, so is most damaging to fruit crops; however, it is a polyphagous feeder that may feed on fruit, leaves, or seeds of many ornamental plants as well. Landscape managers may become most aware of this new pest in the fall when it aggregates in very large numbers on trees or within dwellings, often becoming a nuisance pest. More information is available at http://www.ipm.ucdavis.edu/pestalert/pabrownmarmorated.html.
Adult brown marmorated stink bug.
Bagrada Bug. The Bagrada bug, Bagrada hilaris, a colorful stink bug much smaller than the brown marmorated stink bug, prefers to feed on crucifers. It is a seed and bud feeder that can be very damaging to cole crop vegetables such as broccoli and cauliflower. In the landscape it can become very abundant on alyssum, stock, candy tuft, and mustards. The best strategy for landscapes infested with this pest is to replace alyssum and other hosts with alternative plants that it does not feed on. Populations of this pest have expanded their range from southern California up to Monterey County and will likely move further north soon. More information is available at http://www.ipm.ucdavis.edu/PMG/PESTNOTES/pn74166.html.
Bagrada bug nymphs and adults.
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.