00:03:52 Donald
Here are these palm pests I want to talk about today. And the first one, the South American palm weevil, I think I talked about at another one of our webinars, so I will go over that one quickly. But the other four, the invasive shot hole borer, the giant palm borer, the date palm plant hopper, and the red date scale, I don’t think I’ve discussed with you those, those pests, and the fact that we have them down here means that- you might not have them up there yet.
00:04:39 Donald
although I heard that the invasive shot hole borer is now in the Bay Area. But you probably don’t have these other four, none of these pests there yet. But the fact that they hitch rides on palms and the fact that we have them down here means that they could show up in the Bay Area, so it’s good to be aware of them. Okay, so this is what the South American palm weevil does. This is in San Diego.
00:05:11 Donald
It’s basically in San Diego County. It’s pushing north all the time. It has to jump across about a 15-mile area without many palms, which is Camp Pendleton between San Diego and San Clemente. But I think it’ll eventually broach that sort of natural barrier there and appear in southern Orange County in the not too distant future. So it’s moving north all the time, and this is what it does.
00:05:44 Donald
In fact, it’s killed thousands of Canary Island date palms in San Diego, and now it’s jumped on to other species, because although the Canary Island date palm is the primary host, because it’s so big and offers so many places for hiding and nesting and breeding, laying eggs, it has a big apical meristem that they eat, that the larvae eat, once it finishes off the Canary Island date palms in the area, it’ll move to other species. So there’s the beetle. It’s actually a weevil, which the weevils are characterized by that long snout which they use for gouging out tissues. And the South American palm weevil is native to tropical America. It’s been killing palms in Tijuana, in Baja, California, Mexico, since 2010.
00:06:48 Donald
It was trapped in San Diego since 2010, but wasn’t actually attacking palms until 2015. It’s also been trapped in the Imperial Valley in California, and in Arizona and in Texas. As of April 2021, it was as far north as San Marcos. And I wouldn’t be surprised if it’s up in oceanside by now, which is the last landscaped area before you get to Camp Pendleton, and beyond that, southern Orange County.
00:07:24 Donald
It’s common host is the Canary Island date palm, because, like I said, so many places, a lot of leaves, a lot of crooks and crannies where the weevil can hide, where it can lay eggs, and has a big, big trunk that the larvae can burrow into and feed. The other thing about the South American palm weevil that is often overlooked is that it vectors a disease called red ring disease. It’s actually a nematode, microscopic worm, and that will often kill the palm before the beetle actually, or the weevil actually kills it. Fortunately, red ring disease has not yet been detected in the United States. But that’s kind of typical of vectored diseases.
00:08:19 Donald
They often lag behind the frontal boundary of the vector that’s spreading. So we can probably expect the red ring disease to be here eventually, also. These are some additional palm hosts that they found. The South American palm weevil on. The Brahea edulis, the Guadalupe palm, Jubaea chilensis.
00:08:48 Donald
There are a few in the Bay Area, Phoenix dactylifera. I’ve seen them in the Bay Area, Phoenix reclinata and Sabal bermudana, which is kind of a rare species. And I wouldn’t be surprised if there are other palms that are now being attacked by the South American palm weevil. So here you see a Canary Island date palm in- south of San Diego.
00:09:19 Donald
And if you look up at the canopy, you see that some of those new leaves, especially about 2 o’clock or 3 o’clock look like something’s been chewing on them. And that’s exactly what’s happened. That’s the South American palm weevil. So here’s a closer view of it. So when those leaves were down in the apical meristem and not yet unfurled, the larvae were tunneling around in there, and they would make galleries periodically across these spike leaves.
00:09:56 Donald
And that’s where that kind of feeding damage, occurred. Sometimes you’ll see the tips of the newer leaves, truncated, that’s also damaged from the palm weevil. Notice that you see the damage first on the newer leaves. That’s because the larvae that are causing the damage are down in the apical meristem area where the new leaves are being produced. Here’s some more.
00:10:24 Donald
It shows the advancing stages of the disease in San Diego. The upper left you see a Canary Island date palm that looks like the canopy is starting to tilt. That happens too. You might not see a lot of actual leaf damage, chewing or truncating of leaves, but the burrowing larvae can weaken the stem that’s supporting the apical meristem, and the whole top can start leaning. Over on the right, you see a pretty advanced stage of the weevil.
00:10:57 Donald
Again, it’s the- You always see the damage at the top, at the newest leaves, and the palm will die. And maintain a skirt of healthy looking green leaves down below before those eventually turn brown also. So here you see another Canary Island date palm, which is probably the apical meristem of this one’s probably dead, but it’ll retain these green leaves for a while. So again, these truncated leaf tips.
00:11:32 Donald
Sometimes they aren’t the tips. Sometimes you’ll see sort of a figure seven carved into the leaf, as you see here, missing pinnate. Base of the petioles often have these, these grooves, these gouges that the larvae have made, and they’re often filled with frass, that fibrous sawdust like material. In fact, a good place to look first if you see some visual symptoms up on top of the canopy is to look underneath the palm and look for fallen leaf bases and maybe even some cocoons. And I’ll show you those in a minute. So here’s what these gouges look like in the leaf base, rapedio.
00:12:21 Donald
And a palm with a pretty advanced infestation. Over on the left is an early stage of the infestation, and over on the right is, of course, a dead palm. So these are the cocoons. They look like shredded wheat. If any of you remember that kind of cereal.
00:12:50 Donald
Put that in a bowl and add some milk and raspberries, and you’re on your way to a very nutritious breakfast. You can often find these underneath the palm if it’s been infested for quite a while. And there you see a cocoon with a pupa inside. So how do we manage the South American palm weevil? Through sanitation, prompt removal and disposal of infested palms.
00:13:25 Donald
Proper cultivation is important, meaning water, fertilizer, mulch. It doesn’t mean that the palm won’t be attacked, but if the palm is attacked, you are able to arrest it and get rid of it. A healthy palm is much more likely to recover better than one that’s already stressed from another problem. So avoid wounding palms, because the wounds give off a chemical signal to the adult weevils and it will attract them. The strategy of applying contact pesticides prophylactically, especially after pruning and to protect valuable specimens, has been employed in areas where palm weevils are active.
00:14:17 Donald
And then mass trapping with pheromone baits and a pesticide is also another strategy. So if you want to save the palm, you have to get on it right away when you first see signs of infestation, because once it’s advanced just a little ways, it’s typically too late. So there are some traps. You can make your own out of a three gallon bucket with some burlap on the outside. And on the lower right is Mark Hoddle from UC Riverside, who is really the point person
00:14:57 Donald
for this infestation. If you’ve ever heard him speak, he’s very enjoyable and has a very, very good sense of humor. And there’s a trap. This is down in an area in the Sweetwater river area just south of San Diego, where there is a riparian area with a lot of wild or naturalized Canary Island date palms that were being killed. And this is how many weevils you can get in one of these traps.
00:15:35 Donald
This is purportedly the best trap, and these are available commercially. There are a few diseases and disorders that can mimic the South American palm weevil, and they’re mainly diseases and disorders that affect the palm, where the new leaves are being produced. So, again, if you see something on the lower leaves of the canopy, it’s probably not the South American palm weevil, it’s something else. But all these that I list here are pink rot disease, fusarium wilt, power line pruning, two tiered canopy mineral deficiencies. I’m talking about the micronutrient deficiencies here that always appear on the newest leaves.
00:16:24 Donald
First planting and transplanting, and then water stress. We saw water stress palms prior to the 2022/23 winter, and we thought they could be the palm weevil, but it turned out it was just water stress. So, again, these diseases and disorders that can mimic the South American palm weevil appear on the newest leaves, like the South American palm weevil. So if you think, if you see things on the lower leaves in the canopy, it’s probably not the South American palm weevil.
00:17:08 Donald
Okay. The invasive shot hole borer. This is another beetle that also vectors a disease. In this case, it’s a fusarium disease caused by the fungus fusarium, and it causes dieback on trees and shrubs and other woody plants. And it has been attacking palms, and we used to call it the polyphagous shot hole borer.
00:17:40 Donald
But then a second, nearly identical species of beetle was discovered in San Diego, and that one could only be distinguished from the first one by looking at its DNA. So they just lumped them together and called them the invasive shot hole borers. And they’ve been attacking a wide variety of trees for more than 15 years now in southern California. And like I said, I heard that it was detected in the Bay Area recently. It has a wide host list.
00:18:15 Donald
It attacks over 200 woody species, including some palms, and it does vector a fungal complex that causes fusarium dieback. And the fusarium dieback attacks over 130, nearly 140 species of woody plants, including a few palms. So just because you have the invasive shot hole borer doesn’t necessarily mean you’re going to have the fusarium also. But there’s a good chance that you will. And the fusarium grows in the galleries that the borer makes, and then the larvae feed off that fusarium.
00:19:03 Donald
So it’s there for a reason, that the beetle carries it with it for a reason. It’s food for the larvae. So the beetle’s name is Euwallacea, and I put species spp. because there’s more than one species involved, and it causes this fusarium dieback, which is actually a complex of fungi, but the primary one is fusarium, and that’s why it’s called the fusarium die back, but the graphium and paracrimonium are also present.
00:19:38 Donald
Those are other fungi. So the female beetles are very small and black, less than a 10th of an inch long. The males are wingless and smaller, and not black. They’re brown. The fungi carrying females land on a host, bore into the wood, lay eggs, and inoculate the area with the fusarium complex.
00:20:07 Donald
The larvae feed on the fungi, and mature siblings mate. Fungi carrying pregnant females depart through the entry hole made by their mothers, and they spread to another susceptible host. This is a tropical beetle. It’s most active in the summer. And in southern California, at least during the summer, is when populations and damage can spike.
00:20:40 Donald
When this beetle was first detected, I think it was avocado trees in Los Angeles County, there was near hysteria about it. And when it started attacking multiple hosts, everybody- not everybody, but many people, were saying it was the end of the urban forest as we know it in southern California. Well that didn’t turn out to be true.
00:21:08 Donald
In a lot of cases where you have an invasive species, after the first wave comes through, it tends to plateau out or drop to another level and is not quite as bad. And we think that’s because probably some predators find it and get onto it eventually. So, fortunately, it didn’t turn out to be the end of the urban forest. These are what the beetles look like. I put some tape over some entry holes and after a few days came back and you can see that the beetles were trying to migrate out of this palm via one of the entry holes and they got trapped on the tape.
00:22:00 Donald
So that’s what they look like. So three possible scenarios happen with this invasive shot hole borer. The host can repel the shothole borer without a fungal infection. The shot hole borer successfully bores into the host trunk, spreads the fungus, but does not produce offspring. Or three.
00:22:30 Donald
The shothole borer successfully bores into the host trunk, spreads the fungi and produces offspring. So the third scenario is the most serious, and we call those reproductive hosts.
00:23:14 Donald
So they make small, precise entry holes, very neat, as if a drill had done it. And there’s often some gumming or stained or darkened surface tissues adjacent to the hole. And sometimes you’ll find fine sawdust like frass. However, there is no whitish, sugary exudate as is common in non palm woody plants.
00:23:45 Donald
If you see this shothole borer on oaks and other non palms, there’s typically a whitish, sugary exudate surrounding the, the entry hole. But we haven’t seen that on palms. I have to keep muting it. I don’t know why that is. Okay, so here’s a shot hole borer.
00:24:24 Donald
You can see the small holes. This is in a kentia palm, which is a palm that’s probably not too common in the landscape in the Bay Area. I know there are some there, but you might, you might see it much more commonly inside office buildings. So you can see those small holes, and there is some frass around these holes.
00:24:49 Donald
Here’s another. Another kentia palm. How he forced a way out.
00:25:00 Donald
It has a lot more frass on the trunk. So you see these, where there’s a clear trunk, typically, and there’s a lot of frass on this one. If the fungi successfully colonizes the palm, the wood turns dark brown to black surrounding the galleries. And you can see white fungal mycelia sometimes inside these galleries. However, typical wilt symptoms and eventual palm death have not yet been attributed to the ficus, dieback and palms.
00:25:40 Donald
There’s a possibility, however, that the mechanical damage made by the beetle boring into it could allow other diseases to enter, like pink rot or theolabiopsis. So here’s a palm that we took down in Orange County that was heavily infested. And on the photo on the left, you see the dark areas, and you can actually see some galleries that have been severed when we cut this palm up. And you notice that the general dark area of the tissue that surrounds the- I don’t know if you can see my cursor.
00:26:28 Donald
Can you see the cursor? Yes. So you can see this margin here. So this is all consumed with the fusarium complex of fungi. And here’s a close up of some of these galleries.
00:26:48 Donald
And you notice how the tissue right around them is dark from the fusarium. And there’s at the tip of that knife, you can see a larva of the shothole borer. So actually, palms have trunks that are very good at stopping advancing infections. That’s because they have very strong fibers in them. And I think I went over that during one of our first meetings where I talked about, briefly, about the biology of palms.
00:27:22 Donald
So they don’t have a vascular cambium that encircles the trunk. They have separate phloem and xylem tissues, and they’re each combined in small bundles. And these are scattered across the palm trunk, and they’re very resistant to decay. There’s a close up view of some galleries with the white fusarium complex fungi in them. This was a species of dypsis, like the areca palm.
00:28:04 Donald
Now it’s called chrysalidocarpus. That a species is susceptible to the invasive shothole borer and even the ficus dieback does not necessarily mean it will always show symptoms or die. Why some members of the same species die while others continue to thrive is not well understood. So using these avocado trees as an example, in 2000, I think it was 2010, I looked at heavily infested avocado trees in Long Beach. And this was at the beginning of the hysteria about shothole borer.
00:28:52 Donald
And in Arcadia, at the arboretum on coast live oak. And the pronouncement was that, oh, these trees don’t have long to live. Well, the trees are still alive today, and you can barely tell that they were ever attacked, so fortunately, they didn’t die. And as to why some of them didn’t, that hasn’t been resolved yet. So the shothole borer currently attacks ten palm species, and it looks like four of these are susceptible to the fusarium dieback.
00:29:32 Donald
So here are the ten palm species, king palms, you might have up in the Bay Area. I know you have Mexican blue palms, pindo palms, Cocothrinax probably not, or maybe a few collectors in the Bay Area have them growing. Dypsis plumosa, which is now chrysalidocarpus. That was the palm from which I was showing you the photos of the galleries. Kentia palm, Chinese fan palm, California fan palm.
00:30:11 Donald
I know that there’s probably some of those in the Bay Area, and the foxtail palm, which Home Depot has a habit of selling those, so if Home Depot is selling them, they might show up in the Bay Area. So these are what these palms look like. That’s Brahea armata on the left and Butia odorata on the right, coccothrinax argentea on the left. Dypsis plumosa on the right, kind of dypsis plumosus. Sort of looks like a queen palm, Wallichia disticha, Wodyetia bifurcata, king palm on the left, Kentia palm on the right, Chinese fan palm on the left, and Washingtonia filifera on the right.
00:30:59 Donald
California fan palm. Okay. The giant palm borer
Dinapate wrightii
. This borer attacks a native California fan palm in its desert habitat in the Coachella Valley.
00:31:20 Donald
It evolved with the California fan pump, so it occurs naturally with these palms and primarily attacks stressed, diseased, and dying palms. It was nature’s way of calling out these weakened specimens from the population. However, it occasionally attacks- it comes out of the natural populations in the Coachella Valley and attacks cultivated fan palms and date palms in the landscape, so it could be carried north to the Bay Area. So this is what it looks like, the damage you see on date palms, phoenix dactylifera in the landscape,
00:32:13 Donald
and these weren’t well irrigated, so they were more attractive to the giant palm borer. Infested trunk typically has pretty large exit holes, and these are often plugged with sawdust and frass. Palms can fail and fall, die, or live on, but in a stressed condition. So it’s not-
00:32:45 Donald
Just because this borer enters the palm, it doesn’t mean that that palm is completely doomed. So, again, we’re not sure exactly why. So there’s a phoenix dactylifera trunk showing the exit holes. They’re pretty large. I could stick my index finger in those.
00:33:13 Donald
So, compared to the shothole borer, they’re very large. And here you see some- you see them plugged with the frass, I guess. Yeah, you see them plugged with a frass. The black beetles are about two inches long.
00:33:30 Donald
They fly to stressed, dying, or even, or diseased palms. Females burrow into the leaf bases, they construct nest chambers and mate. The larvae burrow all throughout the palm, including the trunk and apical meristem, sometimes for years before any damage is noticed. There’s a larva of one in a date palm, and there’s the adult. So it’s different from a weevil.
00:34:11 Donald
Doesn’t have that long snout. So the way to manage the giant palm borer is maintain palms in a healthy and vigorous state, paying particular attention to appropriate irrigation, nutrition, and transplanting practices. So we don’t want to stress the palm, because then it becomes like a magnet, for these borers. There are some natural predators of the giant palm borer, including birds like the common flicker and the ladderbacked and gila woodpeckers that might be good in the Coachella Valley.
00:34:50 Donald
I’m not sure if those birds would be elsewhere if, for example, up in the Bay Area, a California fan palm showed up that was brought in for- for landscaping, showed up with a giant palm borer in it. So in those cases, you might have to rely on a systemic pesticide applied to the root zone so that the palm takes it up inside its-
00:35:23 Sophia
Are there any systemic pesticides that have been shown to be successful after infestation?
00:35:32 Donald
Yes. Imidacloprid and dinotefuran have- have been on the South American palm weevil. So I would assume it worked on the giant palm borer also.
00:35:47 Donald
But again, you’d have- because they take a while to be- to move up into the palm, you got to get on it right away. Or if you were maintaining a landscape, especially a high end landscape, and this beetle or the borers were in the vicinity, you might want to consider prophylactically treating the palms with a systemic material and actually a canopy spray, because a contact spray, in case there are any up in the foliage.
00:36:31 Donald
But the best long term solution is probably systemic.
00:36:38 Sophia
Yeah, that’s easier to apply as well. All right.
00:36:43 Donald
I know in Southern Europe and the Mediterranean, where they’re dealing with another kind of palm borer. The red palm weevil, which is closely related to the South American palm borer weevil. I mean, they actually on, on very choice specimens, like, like the jubaea chilensis, a chilean wine palm, they’ll actually run a pipe up into the canopy of the palm, put a spray head on it, and down below, they have a quick coupler release, and they just drive or bring up a tank full of pesticide, quick couple it, spray it for 30 or 40 seconds, drenching the canopy area. And that’s how they’ve prevented these really choice palms from being infested.
00:37:39 Donald
But again, it requires repeated applications, something that I’m not sure we want to do in the landscape. Okay. A little plant hopper called the date palm plant hopper, which can be a problem on date palms. Phoenix dactylifera. But it’s mainly on phoenix robellini, the pygmy date palm, at least in our landscape.
00:38:05 Donald
And it gets way down in the emerging leaves. And the feeding damage from the hopper gives the leaves, yellow spots. You don’t see it until the leaves unfurl. By that time, the weevil is not there anymore. It’s still down deeper inside.
00:38:27 Donald
Not the weevil, the hopper, and the yellow spotting you see later. As I said, it’s primarily on Phoenix robellini, sometimes Phoenix dactylifera. It mostly feeds on unopened developing leaves, resulting in yellow spots as a leaf unfolds. And if you get your hands down there and kind of spread those leaves apart, you’ll sometimes see honeydew, which attracts ants and can make sooty mold and also some frass. So this is what happened when I pulled leaves quite a ways apart.
00:39:07 Donald
You’ll see different life stages. You’ll see ants. And there was some honeydew down in there. This is Phoenix robelinii, and, of course, yellow spots once the leaves emerge. Okay.
00:39:27 Donald
For this leaf hopper. Excuse me. It’s best to keep the palms growing in a healthy manner. And I think this might be able to control it with a foliar spray, just making sure that you get the material way down in the base of the leaves in the center of the plant. I think it’d be easy to control because it’s not inside the plant, it’s on the outside, as opposed to the borers and the weevils being inside the plant.
00:40:03 Donald
Okay. Red date scale is kind of a new pest for me. I’ve heard people talking about it down here, and it. It’s called red date scale because the scale itself is red, but it surrounds itself with this white, waxy material. And that’s what you typically see first.
00:40:25 Donald
You don’t actually see the red scale itself. You see all the white, waxy material thinking, oh, maybe I have a mealy bug, but it’s actually the red date scale. So it originated in North Africa and the Middle East and arrived on date offshoots that were being brought into the U.S. to establish the date industry in the late 19th and early 20th centuries. They’re typically hidden deep down at the base of leaves and or in the leaflet folds along the rachis of the leaf. And they produce copious, white, waxy, cottony material, like mealy bugs do, in which they hide.
00:41:07 Donald
And as I said, the material is actually more conspicuous to you than the actual scale. The adult females are best for identification. They’re small, very small, 400 to six hundredths of an inch long. They’re spherical and they’re red to reddish brown. But again, you’ll see the white, waxy cotton material first.
00:41:35 Donald
The hosts are primarily Phoenix, including canariensis, dactylifera reclinata and robellenii and Washingtonia filifera. It also goes on some non palm hosts, like pandanus and eucalyptus, and seems to be more prevalent on already stressed palms. So palms that are stressed because of nutritional issues, irrigation issues, other disease or pest issues tend to harbor larger populations of the red date scale. Damage is primarily a decrease in normal plant metabolism. So you see poor color stunting and loss of vigor, which could be due to any number of pest diseases and disorders, as other symptoms are chlorosis and necrosis, premature leaf senescence, rarely death.
00:42:46 Donald
But, these other symptoms mimic. These symptoms mimic a lot of symptoms from other problems on palms, pest diseases and disorders. And one of my colleagues, Paul Santos, with Plant Pulse Diagnostics down here, thinks that the Dothiorella, which is kind of an opportunistic fungus, might be facilitated by the damage that the red date scale does. The red day scale might facilitate the entry of Dothiorella. So that’s an interesting proposition.
00:43:36 Donald
So here you see, these are all on Canary island date palms, and they’re from Paul Santos, damaged. You look at the base of these leaflets where they’re folded. You’ll see the white in there. And if we looked carefully in there, you’ll see the little red scales. And over on the right, you see leaves that haven’t even really unfurled yet, but they’re heavily infested with the date scale.
00:44:02 Donald
So these are the signs you would see. And here you actually see some of the red date scales. So as with all, if you have the luxury of bringing palms into a site, thoroughly inspect them prior to them arriving. This goes not only for the red day scale, but also for the borers and the weevils. You can’t find everyone, but a thorough inspection would help to prevent it from entering the landscape.
00:44:52 Donald
Thorough, regular monitoring. And because they’re scales and they produce sugar exudate, control ants because ants protect these sap-sucking insects from predators. And that’s because the ants are kind of farming them and collecting the sweet honeydew. Sometimes a strong stream of water can dislodge and wash away scale infestations. But you have to get weighed down in all the nooks and crannies, which is difficult.
00:45:28 Donald
Encourage and promote beneficials. There are some predaceous mites and some predaceous beetles that feed on the scale. If you’re looking at pesticides, try horticultural oils and insecticidal soaps first. They’re the least damaging to the environment and they can offer some control and then contact insecticides and systemic insecticides. Okay, so palm pest summary.
00:46:08 Donald
Minimize plant stress and maximize palm health and vigor. In many cases, that doesn’t mean the palm won’t be attacked. But if you’re successful in fending off the attack, a healthy, vigorously growing palm will recover more quickly. Appropriate irrigation, nutrition, mulch and light practice exclusion scalp frequently. Be vigilant.
00:46:36 Donald
Use yellow sticky cars to monitor pest populations. And when infestations are first noticed, if you can cut them out or cut- if you have to remove the palm and send it to a landfill.
00:47:12 Donald
So I want to talk about irrigating landscape palms and trees.
00:47:29 Donald
And many people don’t realize that landscape water use in California accounts for only 9% of the statewide total of all the water used. That surprises a lot of people. And I actually think 9% is high because for many years it was 4 to 6%. And then when our first drought, first one of our worst droughts came in 2015, 2016, 2014, it almost doubled to 9%. And I think that was because of powers that be, wanted to make a stronger case about clamping down on landscape water use.
00:48:08 Donald
So that 9% can be divided into residential, which is 7%. And then the large landscapes like parks, golf courses and sports fields, about 2%. So here’s a diagram showing where most of the water goes is agriculture, which is almost 80% of the water used in California. And I’m not complaining about that. I like to eat, so I like to see food on my plate.
00:48:40 Donald
But obviously, there’s a lot of areas where agriculture can tighten up its water use, and they have been doing that, and they could make the most savings, probably in agriculture in terms of total quantity of water saved, and they’re doing that. But the idea that we can just neglect the landscape is kind of short sighted, because here are some amenities and benefits that the trees and landscape provide to us. And if we just let the landscape go to hell in a handbasket, we would be really hurting in many ways. And you can see them listed here, and I’m sure there are others, and it would be expensive. So a recent Canadian study found that having ten or more trees on a typical city block, on average, improved the sense of well-being in ways comparable to an increase in annual personal income of $10,000.
00:49:52 Donald
And moving to a neighborhood with a $10,000 higher median income, or being seven years younger. Who can complain about that? It’s expensive not to irrigate. So there are some direct costs.
00:50:08 Donald
Like when you don’t irrigate, landscape plants will die. So cleaning up dead and dying trees, retrofitting irrigation systems and replanting could be enormous costs. And then there are indirect, hidden costs, like lawsuits, increased fire risk, loss of environmental energy benefits and job loss, and reduced economic activity. So the idea that we should just shut the water off to landscape, I’ve always opposed that. I think irrigating the landscape is a critical part of our lives in our society, and we should continue to do it, but we have to do it in a very responsible and appropriate way.
00:50:53 Donald
So, research that University of California has done over the past 30 years shows that appropriate landscape water management can substantially reduce water use up to 30% or more, which would meet most of the mandated cutback goals, and yet still retain our trees and other land plants. So how do we do this? Well, tree selection and planting are really important. The right species for the right spot. So in southern California, that means low water use plants.
00:51:29 Donald
What are low water use plants? Well, California natives are, and so are Mediterranean climate plants. Because California has a Mediterranean climate, one with cool, hopefully moist winters and warm to hot, rainless summers, plants from similar climates around the world tend to grow well here. So appropriate species are environmentally well adapted, and they fit the intended landscape use.
00:52:02 Donald
Plant it correctly, plant it grade, no organic matter in the backfill. That surprises a lot of people. But studies have shown that incorporating organic matter in the backfill doesn’t help at all and actually can be detrimental. Apply mulch and water judiciously. So what is judicious irrigation?
00:52:24 Donald
Well, there are a couple of ways to do this. One is the twelve-two rule, and I will take responsibility for this. I sometimes call it the Hodel rule of thumb when it comes to irrigating. And that is the goal is to moisten the upper twelve inches of the root zone at each irrigation event. Okay. So that’s what we want to do.
00:52:55 Donald
That next question is, well, when do we do that? Well, when the upper twelve inches of soil reaches 50% depletion, then irrigate again to moisten the upper twelve inches of soil. So what’s 50% depletion? Well, this is where my rule of thumb comes in. If you dig down below the soil surface and one to two inches deep, it turns dry, then it’s time to irrigate.
00:53:25 Donald
That’s pretty close to 50% depletion. It’s close enough so you don’t irrigate again until the upper twelve inches of soil reaches 50% depletion. So you have to become intimately involved with your landscape, with the soil, looking at it, digging down, and after a while, this will become second nature to you. There’s another way to do it, and this is called precision scheduling, where you use real-time or historic evapotranspiration rates, which are available online. Even real-time data is available through the CIMIS irrigation and management system, which is a network of computer-driven weather stations around California that generate daily ET rates.
00:54:18 Donald
And we use that with a crop or species factor, which is a percent of ET for the site. And then when the daily crop or species accumulates to 50% of soil moisture in the upper foot, then it’s time to irrigate. So if we track daily ET, say we had a sandy soil, which holds about an inch of water per foot, when daily ET accumulated to half an inch, 0.5, then we would irrigate and apply that 0.5 back on the soil. So say on a cool day in the Bay Area, or maybe-
00:55:04 Donald
Yeah, maybe on an average day in the Bay Area, maybe daily ET is 0.1 inch. So after five days of 0.1 inch, you’d reach that half inch, and then it’s time to reapply it to the zone. If you’re in Sacramento in the summertime, you might have a daily ET of 0.25 inches, which means it would only take two days to accumulate that half inch. So that’s when you would apply it. Now, clay soils hold two to three inches of water per foot of soil, so you can wait longer between irrigation events.
00:55:39 Donald
But then you have to apply more at each irrigation event also. So those are two ways to do it. The Hodel rule of thumb and using evapotranspiration data. Some of you may be familiar with ET data already, and maybe you even know people who use it, or you’re using it, I’m not sure. So, appropriate application includes water to the root zone, the correct amount applied with no waste or runoff.
00:56:12 Donald
And to do this, I think microsystems are best. We’re talking about drip or micro sprayers here. So, three basic principles of landscape irrigation. Improve system performance. Improve irrigation and water management practices.
00:56:31 Donald
Adjust plant care practices. So that’s really important. So pruning, excessive pruning at the right time, avoiding excessive fertilizer, and using mulch are all important. So there are some poorly crafted water conservation rules out there, like two days per week, 15 minutes run time per station. Some of these are horticulturally unsound.
00:57:06 Donald
They don’t take into account sprinkler precipitation rates, soil types, soil infiltration rates, especially soil water holding capacity, plant type, rooting depth, and evapotranspiration rates. So this used to always irk me when the powers that be were telling us how to water plants. When they didn’t know how to water plants, they never worked around plants. They have no knowledge or experience like you folks do. Okay, so I think-
00:57:42 Donald
I think I can end here because I’m sure we’re at 9:30 now. Just take these take home messages: Trees are essential components of our landscape, and we have the research to show that we can have our trees and save a significant amount of water and still meet the water restrictions.
00:58:04 Donald
And landscape industries have been leaders in judicious irrigation. And trees and landscapes are worth every drop of water and every penny we spend on them because they bring so many amenities and benefits to us.
