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Watch Out For Invasive Shot Hole Borers on Your Landscape Trees

Watch out for these insects! Invasive shot hole borers (ISHB) represent two related species of beetles (polyphagous and Kuroshio) in the genus Euwallacea. Both spread fusarium dieback, a disease that restricts the flow of water and nutrients in the tree, resulting in dead branches, dropped limbs, and even death. Over 60 species of native and non-native ornamental trees and avocados in Southern California are susceptible the ISHB/fusarium dieback complex.Examples of known hosts of the ISHB/fusarium dieback complex include: Box Elder (Acer negundo), Avocado (Persea americana), English Oak (Quercus robur), Valley Oak (Quercus lobata), California coast live oak (Quercus agrifolia), Big leaf maple (Acer macrophyhllum) silk tree (Albizia julibrissin) Liquidambar (Liquidambar styraciflua), Coral tree (Erythrina coralladendron), California sycamore (Platanus racemose), Blue Palo Verde (Cercidium floridum), Purple orchid tree (Bauhinia variegate), Kurrajong (Brachychiton populneus); and many species of Acacia.

The beetles are native to Southeast Asia and were likely introduced into California in shipped goods, wood products, or packaging. While tiny (about the size of a sesame seed), they are prolific, tunneling into host trees and living and reproducing in galleries while feasting on the disease-causing fungus they spread from tree to tree. Females are black and much more common than the small wingless brown males, which are rarely found.

adult ishb (photo by G. Arakelian)

While the initial infestation occurred in Los Angeles County in 2003, beetles travel about 12 miles a year and have now spread fusarium dieback into Orange, San Diego, Riverside, San Bernardino, Ventura, and Santa Barbara Counties. Orange County alone has spent millions of dollars removing infested trees and managing the spread of the ISHB/fusarium dieback complex.

Identifying ISHB in a timely way is essential to reduce damage and slow its spread. Look for round borer entry holes about the size of the tip of a medium ballpoint pen. Staining, gumming, discoloration of wood beneath the bark, and/or frass (sawdust-like material) are other common signs and symptoms. There may also be white powdery exudate around beetle entry holes. Keep in mind that there are many other disorders that have similar symptoms. For example, other fungal diseases produce exudate and staining and other types of borers leave entry holes of various shapes and sizes.

multiple entry holes on avocado (photo by Eskalen lab)
discoloration of wood from fusarium dieback (Photo by A. Eskalen.)

To date, no effective control measures have been found once trees are infested, although entomologists and plant pathologists from the University of California, The USDA Forest Service and other agencies continue to research viable integrated pest management options including biological control.

To prevent and/or reduce spread of ISHB/fusarium dieback:

- Bring only ISHB-free greenwaste (used for mulch and soil amendments) and firewood onsite. Both products can harbor ISHB which can persist for months.

- Treat infected wood onsite whenever possible. Wrap or completely cover wood that cannot be immediately treated and wood that is moved offsite for treatment elsewhere.

- Chipping infested wood to 1 inch or less can kill 95% of the beetles, while solarizing it using a clear tarp eliminates both ISHB and spores produced by the fungus. Logs can also be solarized. Composting is another option that, when done correctly, can kill both beetles and fungal spores.

- Untreated logs, branches, or woodchips infested with ISHB should not be used for firewood or mulch.

- Remove stumps as well as dead trees.

- Follow International Society of Arboriculture pruning standards and never top or flush cut trees which leave open wounds.

- Spray a 70% ethanol solution on equipment and tools since fusarium fungi can adhere to both.

- Keep trees healthy (water mature trees deeply and infrequently, avoid over or under-fertilization, etc.).

- Monitor susceptible tree species often to identify damage as early as possible. Useful detection and reporting tools and more detailed information on the ISHB/fusarium dieback complex can be found here: ucanr.edu/sites/pshb

For more detailed information on the ISHB/fusarium dieback complex, please visit these websites: https://ucanr.edu/sites/pshb/ https://www2.ipm.ucanr.edu/agriculture/avocado/polyphagous-shot-hole-borer-and-kuroshio-shot-hole-borer/ https://cisr.ucr.edu/invasive-species/polyphagous-shot-hole-borer https://californiareleaf.org/pests/

Posted on Sunday, May 31, 2020 at 10:10 AM
Focus Area Tags: Agriculture

Master Gardener Monthly Spotlight: Adam Wagner and Jillian Kowalczuk - Love Starts with a Seed

Jillian and Adam Picture 1

UC Cooperative Extension (UCCE) San Bernardino County Master Gardeners Jillian Kowalczuk and Adam Wagner's passion and enthusiasm for gardening, agriculture, and the UCCE San Bernardino County Master Gardener program made for a lively and fascinating...

Posted on Wednesday, April 29, 2020 at 8:27 AM

Coordinators Corner

grandma in the garden

Finding Community in the Garden  Gardens can mean so many things to people.  They can be a source of beauty and joy, a source of nutritious and delicious food, a connection to our loved ones and people we have lost or young people in our...

Posted on Tuesday, April 28, 2020 at 11:07 AM

Landscape Tree Irrigation to Maximize Tree Health, Benefits, and Beauty

Most trees in California need supplemental irrigation above and beyond what Mother Nature supplies naturally. Even drought-resistant species need regular watering through their first growing season due to their shallow roots. Once trees become established, it's important to water less often but more deeply to encourage deep rooting and structural balance above and below ground. Both under and overwatering can lead to unhealthy trees and even death if the situation is not corrected. Trees receiving too little or too much water exhibit similar symptoms since, in both cases, water is not available to the plant. Trees initially wilt, grow slowly, and develop yellow leaves. Over time, growth stops and leaves become brown and drop. Overwatered trees often develop lower crown and root rot from one or more disease-forming pathogens.

Knowing what type of soil you have (soil texture) is as important as knowing the water needs of your trees. Use the ‘feel test' (pictured below) to find out how much water your soil holds and how often to water. Heavier clay-based soils hold water longer and drain more slowly than sandier soils that need to be watered more often for shorter periods of time.

do a feel test of your soil to help you know when to water

Trees should not be watered on the same irrigation system used for lawns and groundcovers. Soaker hoses and drip systems allow trees to be watered less often but for longer periods of time than your lawn or groundcover. Avoid applying water too close to the trunk. Instead water half-way between the trunk and the dripline of the tree and outward. If you use a garden hose, apply the water on the lowest volume possible slowly, moving the hose every few hours to each of four quadrants around the tree. 

Applying a 3-4 inch layer of mulch around the tree can reduce soil evaporation.  Use only non-flammable mulches in fire-prone areas within five feet from the house and non-contiguous for the first 30' away from the house. In all cases keep mulch a few inches away from tree trunks to keep the trunks dry.

Tip: Before planting a tree, make sure there is adequate drainage. Dig a hole where you want to plant it (the same depth of the pot, which is about one foot) and fill the hole with water. Let it completely drain and refill it. Measure the time it takes to drain one inch using a ruler. If it does not drain more than one inch an hour it is not a good location for your tree. Avoid adding compost or soil amendments to try to correct the problem since tree roots will likely grow in circles, staying within the confines of the amended hole rather than growing outward the confines of the amended hole rather than growing outward.

do a quick drainage test before planting a tree
Posted on Saturday, April 25, 2020 at 1:52 PM
Focus Area Tags: Environment

Volunteer Appreciation

  This week we are celebrating National Volunteer Week by highlighting the volunteers and partners who are a vital part to the success of UCCE programs. On February 24, 2020 UCCE San Bernardino hosted an appreciation dinner to recognize the invaluable volunteers and partners.

  The celebration started with a welcome by County Directors Janet Hartin and Chris McDonald followed by dinner and finally the recognition. Honorees received a certificate of appreciation from UCCE and​ Board of Supervisor Chairman Curt Hagman. Seven San Bernardino County departments were recognized for their valuable partnerships needed to implement programs. The Expanded Food and Nutrition Education Program recognized teachers, school administrators, and parent liaisons who are key in reaching families to provide them with education to live healthier lives. The Master Gardener and Master Food Preserver Programs recognized their indispensable volunteers who are the heartbeat of the program and provide outreach to the community. 4-H recognized leaders who are empowering today's youth to be leaders of tomorrow. To top off the dinner, the Master Gardener Coordinator, Maggie O'Neill, made a delicious cake decorated to represent all programs.

 

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Posted on Friday, April 24, 2020 at 2:23 PM

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