- Author: Ben Faber
- Posted by: Gale Perez
With all the rain last year, even extending into August and now with the rains since December there is a lot of natural ground cover growing, When it gets out of hand, we call it weedy. It might still serve the purpose of protecting the ground from erosion, but it can become an impenetrable mess and if allowed to go into summer, a major fire hazard. In the case of some young orchard, the malva and mustard is bigger than the trees themselves. Getting control of them before they get woody and go to seed is easier earlier than later. So it's time to do something about them if you haven't done so already.
A common practice on flat ground is to mow the middles and then weed whack/whip the tree row up to and around the tree trunk. In the case of trees that have their canopies down to the ground or near the ground or that have created a thick leaf mulch, there's not usually much weedy growth near the trunk. Then weed whacking around the canopy is not much of a problem. If on a slope like most avocados, it's a big, expensive, laborious, hot, sweaty, arduous process of weed whacking. Just waiting long enough for the leaf mulch to create a barrier to weed growth and for the canopies to grow out to rob the sun from the surface undergrowth.
In young trees without a large canopy, it can be a really difficult process of getting those weeds near the trunk. Care must be taken to avoid damage to the trunk. In a couple of recent examples, weed whacking got right up and on the trunks and significant damage was done to the trees. When a wound occurs in any tree, a process kicks in to generate tissue to cover the wound, much like what happens with humans and wound cuts. There's a scar left, but it heals over. If the wound is too large, many trees cant cover the woody tissue fast enough. The wood beneath the cambium ( the green tissue below the bark) is prone to fungal infection and eventually the fungus eats away at the interior of the tree. If the wound is large enough and girdles the tree, all the nutrients from the leaves feeding the roots is cut off. The photosynthate sugars that keep the roots functioning, and the roots stop doing what roots do. This is absolutely true is citrus and most other orchard tree crops. But not avocado.
When making a cross section of most trees, it's possible to see the growth rings – the growth increments that appear each year. The tree starts and stops growth each year and it's possible to clearly identified in what year there was more or less growth. In long lived trees like redwood, it's possible to identify years when certain events happened – the year of Lincoln's Gettysburg Address, for example. This growth habit is called ring porous.
In the case of avocado, it has a growth habit called diffuse porous. There is growth throughout the year and the rings are nor clearly delineated, if at all. It's because of this possible active growth occurring, that the avocado can often cover over damage that is quite extensive. After a fire, given time, mature avocado trees can summon up energy to recover to a great extent. It's not so true of young trees, however. Avocados still have a greater regenerative capacity than a lemon tree, and if the damage is to just one side of the tree, there's a very good chance of recovery.
But these young tree are severely impaired. They do have a chance of recovery, but the damage is extensive and the trunk is fully girdled. Only time will tell if they do recover. If the tree were only a year old, it would be a good idea to pull them and start over. But a number of these trees are three years old and have had a lot of investment in them besides their initial nursery cost – pruning, weeding, irrigation, fertilization, etc. It is heart breaking to see damage like this after so much attention has been paid to them.
And the best thing is to let the tree recover on its own. Use of pruning paint actually impairs tissue regeneration. The grower asked if a kaolin protectant like Surround might be used to provide some sun protection. Since that breathes, it might be a good idea. It might also be a good idea to apply some trunk wraps. These were taken off in order to prevent earwig and snail harbor which can cause significant damage to young trees. But they also provide protection from overly aggressive weed whackers. It is always a compromise when making these decisions.
Original source: Topics in Subtropics – March 28, 2024
- Author: Janet Hartin
Fall is a great time to plant trees in our urban landscapes. Temperatures are cooler than summer and trees adjust to transplanting much better than during the heat of summer.
Why trees? Trees reduce surface temperatures of asphalt and other dark impervious surfaces by over 60 degrees F in inland cities during spring and summer. They also reduce energy usage and costs, enhance habitat and pollinator populations, absorb and store carbon dioxide, provide oxygen for our subsistence, reduce erosion, reduce glare and noise, add beauty to our neighborhoods, and enhance mental and emotional health.
I am appreciative to UCCE San Bernardino County Master Gardener trainee Alex Shippee for his graphic design wizardry, making a drab publication on planting trees inviting and appealing to read.
Have more questions about your trees? Contact the UC Cooperative Extension Master Gardener tree helpline in San Bernardino County. 22trees4tomorrow@gmail.com or our general telephone helpline at (909)387-2182 or email mgsanbern@ucanr.edu where your gardening questions can also be addressed. (You will also reach this website by following the QR code link above.) We also have this handout available in Spanish.
- Author: Karey Windbiel-Rojas
If you are battling with ground squirrels or tree squirrels around your home or property, join us on Thursday, May 19 at noon for UC IPM's one-hour seminar on Squirrels! Dr. Niamh Quinn, UC ANR's Human-Wildlife Interaction Advisor in Orange, Los Angeles, and San Diego counties, will share her insights on squirrel identification, biology, and management. There is still time to register and as always, our monthly webinars are free and open to the public!
https://ucanr.edu/sites/ucipm-community-webinars/
- Author: Karey Windbiel-Rojas
If you are battling with ground squirrels or tree squirrels around your home or property, join us on Thursday, May 19 at noon for UC IPM's one-hour seminar on Squirrels! Dr. Niamh Quinn, UC ANR's Human-Wildlife Interaction Advisor in Orange, Los Angeles, and San Diego counties, will share her insights on squirrel identification, biology, and management. There is still time to register and as always, our monthly webinars are free and open to the public!
https://ucanr.edu/sites/ucipm-community-webinars/
- Author: Beatriz Nobua-Behrmann
- Author: Randall Oliver
- Posted by: Elaine Lander
Two identical looking species of wood-boring beetles, collectively known as invasive shothole borers (ISHB), have killed thousands of trees in Southern California and pose an ongoing threat to California's urban and wildland forests. These beetles, which are not native to the United States, were first identified in Los Angeles County in 2012 and have since spread to six other counties: Orange, Riverside, San Bernardino, San Diego, Santa Barbara, and Ventura.
Beetles, Fungus, and Impact
As the fungus grows, it colonizes the tree's vascular system, blocking transport of water and nutrients. This causes a disease called Fusarium dieback that can kill branches or entire trees. The beetles and their symbiotic fungi have a wide range of suitable hosts, including more than 65 species of trees found in California. The most highly susceptible trees include many of the species commonly used for landscaping, such as sycamores, oaks, cottonwoods, and box elder trees. ISHB beetles attack healthy trees as well as stressed or diseased trees in a variety of urban, suburban, and riparian settings. Visit www.ishb.org to find the full list of reproductive hosts in California.
Female beetles can fly short distances, allowing the pest-disease complex to spread into new areas near already infested trees. Beetles can also be transported in infested firewood and green waste, leading to spread over much greater distances. While beetles have only been identified in Southern California and the Central Coast to date, further spread throughout much of California is possible.
ISHB-infested trees can quickly become public safety hazards. Trees with heavily infested branches can be especially hazardous, since the combined damage of the fungal disease and the beetle's tunneling activity weakens the wood, causing limbs to break and fall. In addition, severely infested trees will become constant sources of beetles that can disperse and infest neighboring trees. Such “amplifier” trees generally need to be removed completely, while more lightly infested trees can be managed or treated without requiring removal. Therefore, early detection and rapid response is the key to controlling ISHB. Substantial recovery in lightly to moderately infested trees has been observed in some areas where amplifier trees have been removed.
Identifying an ISHB infestation
- Beetle entry holes: When the beetles tunnel into trees they make small, perfectly round holes, each about the size of the tip of a medium ballpoint pen (0.8 mm). (Figure 3)
- Additional signs and symptoms: Entry holes are usually accompanied by one or more of the following signs and symptoms, which vary by the tree species: staining, gumming, white powdery exudate, or frass (boring dust).
- Dieback: Dead or wilting branches can be a sign of a severe infestation. If you see dieback on trees, check for entry holes on the trunk or the branch collars.
In addition to visual inspections, traps using quercivorol, a plant-based lure that attracts the beetles over short distances, can help determine the presence and abundance of beetles in an area. Trapping is especially useful for large or inaccessible areas where regular visual inspections of all the trees are not practical. In those cases, trapping can help determine if ISHB is present in the area and can help focus survey efforts on infested trees. Because the lure has relatively low attractiveness, trapping is not an effective control method for ISHB and is only used for detection purposes.
What Can You Do?
- Keep trees healthy. Proper irrigation and maintenance will keep trees strong and help protect them from ISHB and other pests.
- Prune out infested branches. Removing branches that have clusters of 50 ot more ISHB holes would help control this pest. For trees that undergo heavy pruning every year, like avocado trees, removal of all infested branches is recommended. Tools should be disinfected after pruning by spraying them with a solution of 5% disinfecting bleach or 70% ethanol to avoid spreading the fungal disease to other trees.
- Remove severely infested trees. Unfortunately, severely infested trees (with more than 150 entry holes and ISHB-related dieback) are not likely to survive. These trees should be removed as soon as possible, and the stump should be ground to one inch or less. (Figure 4)
- Manage downed wood. Green waste generated by branch and tree removals should be properly disposed.
- Chipping/grinding to one inch or less kills 99.9% of the beetles. If that is not possible, chipping to three inches or less still will kill 98% of the beetles in the wood. In already infested areas, chipped wood can be used onsite as mulch. However, if working on a newly infested area or if the wood chips will be moved to another area, chipping should be combined with solarization or composting to kill 100% of the beetles. If chipping is not an option, logs can also be solarized or kiln dried to exterminate the beetles.
- Solarization involves covering the material with clear plastic tarp and letting the heat from the sun kill the remaining beetles. Chips and beetles should be fully contained by wrapping plastic both underneath and over the material. Chips should remain covered for at least six weeks during the summer months or for at least six months between September and June. The depth of the pile should be no more than 30 inches deep, to ensure even heating.
- Composting, when done correctly, should also kill the remaining beetles in the chips. It is recommended to send infested chips to a professional composting facility that has earned the U.S. Composting Council's Seal of Testing Assurance.
- Prevent the spread. Avoid spreading this pest by not moving firewood or mulch that hasn't been properly solarized or composted. If you must move infested greenwaste (for example, to bring it to a composting facility) make sure the load is tightly covered while in transit.
- Consider chemical control.TreesthatarereproductivehostsforISHB and that show signs of active infestations can be treated with a combination of insecticide and fungicide. The decision to treat a particular tree depends, among other things, on the tree's condition, value, and hazard level. Trees that aren't already infested should be monitored but not treated. There are various chemicaloptionsthatcanbeusedagainstISHB-FD.
- Trunk sprays of a contact insecticide, such as bifenthrin, combined with Bacillus subtilis or tebuconazole (which are fungicides) have been demonstrated to offer some degree of control.
- Systemic soil injections or drenching with the insecticide imidacloprid has also provided control, as has trunk injection with emamectin benzoate (insecticide) combined with tebuconazole or propiconazole (fungicides).
- These pesticides should only be applied by a licenced professional following the instructions on their labels to avoid harming non-target organisms.
Biocontrol options are currently under research. They include the use of natural enemies (such as parasitic wasps from the beetles' point of origin), entomopathogenic fungi (which are fungi that attack insects), endophytes (which are microorganisms that live in the tree that may provide protection) and nematodes. But these biological management options might take time before they are tested and available. Until then, prevention, early detection, and rapid response are our best weapons to keep trees healthy and alive. For more information on invasive shothole borers and their management, visit www.ishb.org.
[Article originally published in the Summer 2021 issue of the Green Bulletin.]
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