Polyphagous Shot Hole Borer and Avocados

Multiple entry holes on avocado trunk. Photo credit: Eskalen Lab, UC Riverside.

Multiple entry holes on avocado trunk. Photo credit: Eskalen Lab, UC Riverside.

Of all the plants in our yard the one I care most about is our avocado tree. I’d be despondent if anything happened to it. Which is why I panicked when I first heard about the Polyphagous Shot Hole Borer (PSHB), a beetle that spreads a fungus Fusarium euwallacea. First noticed in 2003 here in Southern California, the PSHB seems to damage some trees more than others.

Concerned about losing my avocado tree I wrote Akif Eskalen, a plant pathologist at the University of California, Riverside. Dr/ Eskalen’s lab has done a lot of work on the PSHB and what to do about it. I asked him specifically about avocados and here’s what he had to say in an email,

My lab has been conducting a continuous survey on PSHB on infested and non-infested avocados in California since 2012. Based on the preliminary results from our survey the beetle PSHB seems to be attacking and causing damages on primary and secondary branches of avocado only. We have also seen attacks on the trunk of the trees but somehow the beetle is not successful establishing galleries there which could cause of quick death of the tree. I believe with a proper orchard sanitation you can reduce the damage of the beetle and also keep the beetle population down in the orchard . . . we are still continuing experiments with different insecticide and fungicides on avocado against this beetle and their fungi. An insecticide (Hero) has already registered under Section 18 that could be used by growers in CA.

He provided a link to a short publication his lab put out on orchard sanitation best practices as well as a link to information for avocado growers on the use of Hero. Hero is a pyrethroid-based pesticide.

For my own backyard tree I’m going to:

  • Make sure pruning tools are disinfected before use. This is one of the main reasons we use a qualified arborist.
  • Avoid moving firewood around. I’m going to have to think carefully about the wood I import for my pizza oven.
  • Use mulch that has been chipped to less than 1 inch.

I’d sure hate to lose a tree that provides six months worth of free and delicious Fuerte avocados.

Attractive Ornamental Flowering Trees

As I mentioned yesterday, I attended a class a tree identification class at the Arboretum taught by LA County plant pathologist Dr. Jerrold Turney. During the course of the lecture Dr. Turney recommended a number of striking, flowering ornamental trees. I thought I’d list a few of those remarkable trees in case you’re considering planting one. While this list is Southern California-centric, many of these trees can be grown in other climates. All images are courtesy of Wikimedia.

800px-magnolia_stellata_in_the_jardin_de_plantes_de_paris_001Magnolia stellata (Star Magnolia)
Small trees go with small houses like gin goes with tonic water. Small trees are also easy to maintain and don’t break the bank when it comes time to call an arborist. This tree is from Japan and will grow all over North America and Europe.

754px-cornus_florida_02_by_line1Cornus florida (flowering dogwood)
One catch with this pretty tree is that it’s susceptible to anthracnose.

800px-ipe%cc%82_roxo_ype-tabebuia_impetiginosa_cemiterio_sa%cc%83o_paulo_brazilTabebuia impetiginosa (pink trumpet tree)
A tough and beautiful tree that’s great for urban locations.


Tabebuia chrysotricha
Of all the trees Dr. Turney showed, I think this one was my favorite. The yellow flowers really pop out against a blue sky.


Brachychiton acerifolius (Australian Flame Tree)
Speaking of popping out, red flowers are also really dramatic.

chionanthus_retusus_-_chinese_fringetree_-_3Chionanthus retusus
Another good urban tree.

To these suggestions I’d add one of my own that also produces a tasty fruit:

redbaronRed Baron Peach
Plant one of these as a bare root tree this spring and you’ll have an attractive small tree and peaches!

Thanks to Dr. Turney for a great lecture. If you’d like to attend the other three parts of his tree identification class you can sign up here.

What’s the Most Squirrel-Proof Fruit?


Depending on my mood I see our yard either as a sort of groovy, permacultural exercise in “abundance” or as an overpriced rodent feeder. It occurred to me this morning that we’ve been, inadvertently, running an experimental squirrel fruit buffet for ten years.

Perhaps it would be informative to see what trays in the buffet have any fruit left for the resident hominids. Towards that end, I’ve created an annoying, animated emoticon scale ranging from one to five squirrels with five being the most favored fruits and one being the least favored.

In the give up all hope category:

Figs: Squirrel Icon by AlephronSquirrel Icon by AlephronSquirrel Icon by AlephronSquirrel Icon by AlephronSquirrel Icon by Alephron
Everyone loves figs. Raccoons, squirrels, rats and even Roman emperors. I’ve even seen raccoons, in the middle of the day, feasting on our delicious Mission fig. It’s easy to see why. There’s nothing like a fresh fig. And fig season is so frustratingly short. Kind of like our youth!

Apples: Squirrel Icon by AlephronSquirrel Icon by AlephronSquirrel Icon by AlephronSquirrel Icon by AlephronSquirrel Icon by Alephron
We have two trees, a Winter Banana and a Fuji. The squirrels are welcome to the mealy Winter Banana apples. But those Fujis are just about the tastiest apple I’ve ever eaten. The squirrels usually manage to get them all.

Persimmons: Squirrel Icon by AlephronSquirrel Icon by AlephronSquirrel Icon by AlephronSquirrel Icon by AlephronSquirrel Icon by Alephron
We have both the non-astringent and astringent types of persimmons. The squirrels like to take a bite out of them before they are ripe, thus leaving them to rot on the tree. Persimmons take so long to mature that I doubt I’m going to get any this year before the squirrels get to them.

Peaches: Squirrel Icon by AlephronSquirrel Icon by AlephronSquirrel Icon by AlephronSquirrel Icon by Alephron
I managed to harvest a few thanks to throwing some netting over the tree. But I was so stressed out by the prospect of finding the tree stripped of fruit that I became unpleasant to live with.

On the more hopeful side:

Avocados: Squirrel Icon by AlephronSquirrel Icon by Alephron
The damage here is more from rats than squirrels, I think. Typically, I’ll find an avocado with one bite near the stem on the ground. The good news is that those partially chewed avocados are, usually, still edible.

Pomegranates: Squirrel Icon by Alephron
I think this is the real winner in the squirrel/human fruit buffet fight. I’ve found squirrels trying to eat them but they have to chew through the thick and unappetizing skin. Plus the tree has hidden, wicked thorns. The downside is that these two qualities also make them difficult to harvest and eat. I use what we call the pomegranate spanking method to release the seeds. Squirrels have not yet figured this out.

What fruits do you manage to wrestle from the squirrels? What have you noticed in your garden?

The Fine Art of Determining Peach Ripeness


How do you know when your peaces are ready to pick? For home growers it’s all about color. According to the University of Georgia,

Ground color is the best field indicator of peach maturity. . . The ground color of a peach approaching maturity is light green. A break in color toward yellow is the first definite indication of maturity. Brightening of the red over-color of the skin is another, though less reliable, index of maturity. Red color is typically dull prior to the green to yellow break. When the underlying ground color breaks to yellow, the red brightens and can easily be selected. Color judgments are reliable with many older varieties, but new highly colored varieties with higher percentages of red over-color have diminished the usefulness of color in maturity determination.

Farmers have access to a few tools that can make ripeness determination easier such as this expensive gadget that measures firmness or a brix meter for determining sugar content. These tools could only be justified if you were planning on growing, shipping and selling fruit. More useful for us backyard growers is this gallery of peach fruit color stages.

I’ve been picking them a little on the green side and letting them ripen inside in order to stay ahead of the squirrel menace. This year we’ve eaten a lot more peaches than the squirrels have.

How to Squirrel Proof Your Fruit Trees

IMG_7297We’ve been guilty in the past of claiming that growing fruit is labor-free. That’s a lazy blogger’s lie. The truth is that you have to stay on top of pruning, irrigation, fruit thinning, fertilizing and pest prevention if you want to harvest any fruit. After not getting a single peach off our small tree last year due to squirrels, I vowed to do things differently this year.

I considered a number of squirrel prevention techniques:

  • Metal collars on trunks. This doesn’t work, especially in urban areas. Squirrels are superb acrobats and can simply jump from a roof, fence or adjacent tree on to your fruit tree.
  • Trapping, killing, hunting. I don’t have the heart to do this and it’s illegal in urban areas but it is what professional orchardists do.
  • Electronic or visual frightening devices. According to UC Davis, these don’t work. Squirrels aren’t dumb.
  • Dogs. Maybe, but it depends on the dog. Our late doberman was more interested in alerting us to the mail carrier’s rounds. He was more interested but, ultimately, unsuccessful in his 13 year battle against skunks.

Exclusion with plastic bird netting is the most promising technique for urban areas. In order to do this you need to keep the tree pruned to a manageable size. I purchased a 14-foot by 14-foot piece of bird netting and Kelly and I put it on the tree (it’s a two-person job as bird netting is a pain to work with). We secured it with clothes pins. You must be absolutely certain to leave no gaps in the net. If you leave a gap you could trap birds and the squirrels will also work their way in. The next step is to keep a close eye on the fruit and harvest it as soon as you can, perhaps a little sooner than is ideal.

Unfortunately, squirrels can easily chew through bird netting so this method is far from foolproof. According to UC Davis, exclusionary methods will only work if the squirrels have other things to eat. Another argument for biodiversity in our landscapes, I suppose.

If you know of any foolproof squirrel prevention techniques please leave a comment!