L.A. County Arboretum & Botanic Garden Plant Info: PSHB

Showing posts with label PSHB. Show all posts

Wednesday, June 30, 2021

Great Article on Invasive Shot Hole Borer

The Invasive Shot Hole Borer (formerly called the Polyphagous Shot Hole Borer) is still a threat to native and introduced trees here in California, and although in some cases it seems to be mellowing out just a little bit, it still has the capability of getting worse -especially during the curent severe drought. Here is an article by Rosi Dagit that summarizes that current state of affairs with this pest and also some opportunities to be involved in citizen science efforts to keep track of it.

Tree limb infested with Invasive Shot Hole Borer

Discoloration on bark indicating Shot Hole Borer attack

The Invasive Shot Hole Borer

Wednesday, September 7, 2016

Q. I would like to know the latest information regarding beetles attacking southern California trees and if there is anything that can be done to cure the problem.

A. There are normally hundreds of different types of beetles that attack trees here in Southern California, in fact beetle attack is a normal stage in the life cycle of most trees in the wild. Without beetles attacking trees that are stressed and dying they would take far longer to decompose after the trees have died, and therefore it would take longer for the new trees replacing them to establish.

This normal beetle activity accelerates when stress on the trees accelerates, which is what's happening now because of the current severe drought. When most of the trees in a forest are stressed, the beetles numbers increase to a point where they are so large that even a healthy tree can't repel them.

But there's more. The current level of trade from around the world has increased the number of new beetles that have no natural checks and balances (most of our native beetles are normally kept in check by parasites and predators that feed on them). One example is the Polyphagous Shot Hole Borer (PSHB). The pest was only discovered in 2012 and since then has caused the loss of thousands of trees from the urban canopy here. Since this pest also threatens the $Billion+ avocado industry, there has been significant resources channeled to its control. Still, there does not seem to be an effective control against it, although several compounds are being looked at and an effort is being made to identify predators and/or parasites that can naturally control the pest. Currently it attacks over 100 types of trees and large shrubs, and its host list (the plants it can reproduce in and spread the infestation) has swollen from 22 in 2012 to over 40 now.

What's the answer then? Short term finding controls is important, but it does not solve the problem. The biggest problem and one of the big reasons that the shot hole borer and other pests are getting such a foothold here is the urban forest canopy itself.

Many of our trees are clonal, they are basically the same tree. That is what ornamental horticulture is about is reproducing clones of plants that have the most desirable traits you are looking for. This make for easy pickings for pests because there is no difference in the plants ability (or lack of it) to resist the pest that is attacking. This makes for large numbers of pests and favors the those offspring that are particularly good at attacking and reproducing.

Also our own urban canopy is made up of trees that have evolved to take advantage of climates that are totally unlike ours. For example the beautiful fall color turning tree Liquidambar styraciflua originated from the South eastern coast of the United States. That area has copious amounts of rainfall throughout the summer, unlike Southern California where summers are hot and dry. Why does it do so well here? Two reasons; 1. Irrigation which allows us to grow species of trees that otherwise would not establish here 2. Lack of pests due to the fact that the plant is grown in an area where its native pests are absent. Both of these conditions are unsustainable in the long run and the only cure is to select trees that actually do well with the amount of water that is naturally available here. We will still get new pests but the trees will not be stressed and therefore huge plague-like infestations like the current PSHB infestation are less likely to happen. That does leave us with a much smaller selection of trees to plant, but if we do that we can enjoy a good looking and long lasting landscape dotted with trees.

Cheers, Frank

Tuesday, June 28, 2016

Dying Maple (maybe) Tree

Q. I have this maple tree (I think) has been deciduous since October 2015 and one small branch has a few leaves in the spring. But now it seems to be dying. Can you give me some input what to do? Totally cut down or wait and see? I appreciate your input, thanks!

A. The tree (I think you have a Liquidambar not a maple), appears to be quite dead. The fact it has not leafed out by now is a major consideration in this. You need to take it out as soon as possible as dead trees are 100% likely to fail in the next several years. It is important that you chip the tree completely to pieces that are one inch or less and solarize the chippings for at least 6 weeks (in winter at least three months: see solarizing guide on second page of pamphlet here ) so that if the tree was infested with Polyphagous shot hole borer (PSHB) it does not infest other trees. Many maples and the Liqudambar tree are hosts for PSHB.

Thursday, March 12, 2015

California Landscape Contractors Fund Polyphagous Shot Hole Borer Research

As the grave nature of the consequences of the current Polyphagous Shot Hole Borer infestation become clearer another organization with a stake in plants the pest attacks are donating money for research into methods to control it. Up until now the California Avocado Commission has been the biggest donor, but recently another organization that might have much more to lose, the California Landscape Contractors Association, is funding research. With the majority of the plants being attacked by this pest being important elements in landscape design here, this funding makes good sense for the organization whose members rely on them as the fundamental building blocks of their industry.

Wednesday, December 3, 2014

A Little Light at the End of the PSHB Tunnel.

A relatively new pest continues to wreak havoc on L.A.'s trees and threatens the avocado industry. Until now hope for control of the pest has been slim -but just recently that has changed.

The polyphagous shot hole borer (PSHB) is one of those new pests that makes entomologists and pest control advisors look bad. This small beetle from somewhere in southeast Asia (we think) bores into perfectly healthy trees (we're mostly sure) where it completes its life cycle. It infests more than 200 trees (but that number is growing). Over 30 trees are reproductive hosts in which the borer can reproduce and wreak havoc on other nearby trees (but we're not sure that number is going to stay the same) and many more area adversely effected by the beetle (another number that keeps on growing).

What makes this pest particularly irksome is that it goes after trees that are the heart and soul of what it is to be a Californian: Avocados, Coast Live Oaks, California Sycamores, and many other native California trees. Right now it's in Los Angeles, Orange, San Bernardino, Riverside, and now parts of San Diego counties, but there is nothing, save for its seeming preference for well watered trees, to keep it from spreading to the rest of the state. No pesticide has yet found to be really effective in controlling it -this fact due to the pest feeding only on the fungus that it spreads from tree to tree and not on the wood tissue that traditionally carries insecticides from the roots or trunk where they're applied to the feeding jaws of the target insect.

They are also incestuous, with the small number of sibling male beetles mating with their much more numerous sisters. This means that there is no mating cycle to disrupt because they mate in the moist, fungus filled chambers of the beetles galleries. Galleries that penetrate deeply into the heartwood of the tree so they mate there and not out in the open where a pesticide coupled with a mating pheromone could kill enough of the pests to control them. The best treatment so far has been a once every 6 week bark spray -a frequency of application and amount of pesticide that is far too expensive for most homeowners and growers.

Yes, this pest is depressing. Every time I've talked about, consulted about it, or lectured about it I feel like Debbie Downer on pessimistic steroids. But there is finally some good news. It appears that a pheromone-like compound is effective in attracting the beetle. P-menthenol, a chemical compound called a terpene that has been isolated from among other plants Yarrow, can attract the beetle from over 50 feet.

In p-menthenol could be used to attract the beetle to a concentration of pesticide or spores of a fungus that is pathenogenic to the beetle and allow that beetle to bring those substances back to the galleries from where it first emerged to chase the scent.