Management

Early Detection and Monitoring

Regular monitoring is recommended to ensure infestations are managed early and before trees become hazardous. Early detection enables the treatment of trees when they are lightly infested ensuring the greatest chance of overcoming infestations. Frequent visual inspection of trees is the best monitoring approach. Look for signs and symptoms of ISHB infestation on both the trunk and branches.

Learn to identify the signs and symptoms of an ISHB infestation.

Infestation level within a given tree is determined by the number of active galleries (entry holes) in the trunk and branches, and the presence of dieback associated to those beetle attacks. Only active entry holes with live beetles inside the associated gallery should be considered to determine infestation levels. It is important to note that the entry holes may remain visible on the trunk and branches even after the beetles left or died. The presence of beetles, wet staining, and frass are good indicators that the entry holes are active. One other way to confirm if there are live beetles within the galleries is painting over selected entry holes with water-based latex paint. If an ISHB female is alive within the gallery, it will re-open the entry hole during the next 24 hours, proving that the entry hole is active. 

Monitoring and Sampling Best Practices Video

A video outlining best practices in monitoring and sampling for invasive shothole borers (ISHB) is available on the University of California Integrated Pest Management YouTube channel. View it at https://youtu.be/1LKKJe3NgTY

Trapping for Invasive Shothole Borers Video

To manage invasive shothole borers, it is critical to find infestations early through a regular monitoring program that combines visual tree inspections with trapping. In this video, UC ANR experts share insights and best practices on trapping for this pest. View it at https://www.youtube.com/watch?v=cNPuZUiKz1g.

Management of Invasive Shothole Borers Video

Invasive shothole borers and the fungus they carry can be devastating to the trees they attack, but their presence on your property is not necessarily a death sentence for your trees. With proper management practices, many trees can be saved. This video describes how to monitor for the beetles and how to manage infestations. View it at https://www.youtube.com/watch?v=H8bdgWA0JHk

Cultural and Chemical Management

Management decisions for trees in the urban forest depend on whether or not the tree species is a reproductive host, the level of infestation, tree location, and the potential hazards associated with infested limbs and trunks. Use the ISHB Detection & Management Assessment Tool to help you determine the best steps to manage ISHB-FD infestations and/or refer to the tables below:

ISHB-FD management matrix for infested urban and peri-urban forest (Source: UC IPM Pest Notes, Publication 74149, Invasive Shothole Borers, August 2023)
ISHB Infestation Level & Management Options for Low Value Trees

ISHB Infestation Level & Management Options for High Value Trees

Definitions:

Tree Value†
• High Tree Value: Species of high economic or cultural value (e.g., heritage trees); larger and/or older trees
• Low Tree Value: Species of low economic value; smaller and/or younger trees; trees with undesirable form, structural issues (e.g., codominant branches), or other issues (e.g., other pests)

Hazard Level†
• High Hazard Level: Trees that might pose a high risk to people or property (e.g., trees adjacent to walkways, playgrounds, high-use lawns, parking lots)
• Low Hazard Level: Trees that pose a low risk to people or property

Host Type
• Reproductive Host: Plant species suitable for beetle reproduction and growth of Fusarium euwallaceae or F. kuroshium
• Non-Reproductive Host: Plant species that have not yet proved suitable for beetle reproduction; however, these species might be susceptible to Fusarium euwallaceae or F. kuroshium

Infestation Level, based on attacks (number of entry holes observed)
• Low Infestation Level: < 50
• Moderate Infestation Level: ≥ 50 and < 150
• Heavy Infestation Level: ≥150
• Severe Infestation Level: ≥ 150 + ISHB-related dieback  
    
* If ISHB attack is confined to the branches of host tree, prune affected branches immediately to prevent advancement to the trunk. Prune hazardous branches on high-value hosts and treat pruning wounds to prevent re-infestations.
† Definitions for tree value and hazard level vary. Classification must be determined by site and site use (e.g., economic or cultural value and risk to people or property).
 

For low to moderately infested trees, the removal of actively infested branches as well as chemical treatments with a combination of insecticide and fungicide have proven to be effective control measures. Treatment options include systemic pesticides that can be applied as a tree injection or soil drench and pesticide bark sprays. (See UC IPM Pest Notes, Publication 74149, Invasive Shothole Borers, August 2023 for more specific details of chemical control options.) These treatments are ideally timed in early spring and fall when adult beetles are emerging.

Heavily infested trees (with more than 150 entry/exit holes and signs of branch dieback) often have their vascular system extremely compromised by the disease and may not be able to be saved with chemical treatments. These trees are a big source of new beetles and often become hazardous due to the structural damage caused by the beetles’ galleries. Timely removal and proper disposal of the infested wood is recommended in these cases.

So far, no preventative treatment has been proven effective. Treatment of uninfested trees is not recommended.

A certified arborist should be familiar with best practices with respect to both maintaining trees and disposing of infested wood and green waste. Find a Certified Arborist

Prevent the Spread of ISHB-FD

1. Don't move firewood!
   Many wood-boring pests, including ISHB, are spread by the transport of infested wood. Buy firewood where you intend to burn it. Visit dontmovefirewood.org and www.firewood.ca.gov for additional resources and information that you can share with others.
   
   
   
   
   
   
   

2. Properly dispose of infested material
   Do not use untreated ISHB-infested logs or chips for firewood or mulch. Options for treating infested material include solarization, composting, kiln-drying, and biogeneration. Learn more about these options here.

3. Disinfect pruning tools
   Poor pruning practices can facilitate the spread of plant disease. Any pruning, sampling, or other tools that come into contact with infected wood should be sanitized before being used on uninfected trees. This includes chainsaws and wood chipping equipment. If several infested and uninfested trees need to be maintained on a property, we recommend managing the trees in batches. First take care of all of the uninfested trees, then move to the infested trees so that your tools won't need to be cleaned until the end of the day. 

For pruning and tool sterilization tips, see UC Riverside's "Best Management Practices for Disease in Oak Woodlands" .

Infested Material Disposal

Wood from ISHB-infested trunks and branches is still full of live beetles. If infested wood is not properly handled, beetles will emerge from the cut logs and attack new hosts. This two-step process will help prevent the beetles from spreading to other locations or re-infesting your own property. Details on each procedure can be found below.

Step One

Chip infested wood immediately after tree removal or pruning. Running ISHB-infested material through a wood chipper is one of the most effective ways to kill the vast majority of beetles living in cut logs.

Wood chips from a ISHB-infested sycamore. Source: John Kabashima, UCCE

• Chip as small as possible. The chip size should be smaller than 3 inches. Chipping to 1 inch or less is optimal.
• Do not leave piles of contaminated wood uncovered. If wood cannot be chipped immediately, tightly wrap the logs in plastic to contain the beetles.
• Cover unchipped wood in transport.
• If wood cannot be chipped, tightly cover cut logs and follow directions for solarization or kiln-drying.

Step Two

After chipping infested wood, select one of the options below to ensure that beetles and fungi are destroyed. Some of these methods also work for logs that cannot be chipped. 

Always cover the material in transit when transporting infested plant material to another site for treatment.

Solarization

This method is suitable for handling both infested chips and logs. When done correctly, solar energy will heat plant material until both the beetle and fungi are killed.

How long does infested wood need to be solarized?

Solarization is most effective during the peak of summer, when temperatures are higher and days are longer, but it may be used during other seasons as long as time and space can be committed.

• July - August: Cover chips or logs with sturdy plastic for at least 6 weeks. Temperatures during these months should be regularly above 95°F.
• September - June: Cover chips or logs with sturdy plastic for at least 6 months.

Other tips for proper solarization:

• Use a sturdy plastic sheet or tarp that can withstand rain and wind. Clear plastic is preferred since it lets more sunlight through and heats the content more efficiently.
• Fully contain chips, logs, and beetles by wrapping plastic both underneath and over the material.
• Keep log or chip layers as thin as possible, two logs deep maximum, to ensure even heating throughout the pile.

Composting

Proper composting should kill remaining beetles and fungi in the chips. Composted, chipped plant material may then be re-purposed as mulch or added back into soil to improve texture and water retention.

It is recommended that wood chips be composted at a professional composting facility that has earned the U.S. Composting Council's Seal of Testing Assurance (STA). Facilities in the STA program are tested for proper decomposition and pathogen control.

Find a local STA Compost Facility at the US Composting Council website.

Composting can also be done at home, as long as guidelines for adequate decomposition are carefully followed. See UC IPM for guidelines on composting. Find additional composting tips from CalRecycle.

Kiln-drying

Unchipped, ISHB-infested wood can be decontaminated by the heat used in kiln-drying. To destroy the beetles and fungi that cause Fusarium dieback, it is necessary to heat the material for at least 60 minutes at 140°F. Wood that has been disinfected can then be re-purposed.

Biogeneration

Biogeneration facilities burn green waste and convert it into energy. Learn more about biomass energy here.