Episode 124: Understanding the Complexities of Fruit Trees with Dr. Ted DeJong

Hi, friends. Welcome to the Regenerative Agriculture Podcast. This is John, and today I am delighted to have a conversation that I've been wanting to have for some time, and that is a discussion with Dr. DeYoung on how we can better understand plant physiology and specifically fruit tree physiology from a first principles perspective. For those of you who've been listening to the podcast for a while, you're very familiar with my strong belief that if we truly, deeply understand how something works, then how to manage it becomes very apparent and becomes very obvious. And this is one of the things I think has been missing in so much of agriculture, is we do things without necessarily understanding how they work very well. So I've been looking forward to this discussion for quite some time. Thank you very much for joining us. Can you tell us a bit about the genesis of your work and the scope of your work?

So I've been at the University of California for about 40 years now. My, my research was primarily in stone fruits, peaches, plums, and nectarines. And like you just stated, I, my, my strong desire was try to understand how plants work. And I've also taught homology or physiology of fruit trees to students, graduate students and undergraduate students and growers for the whole time they've been in, in at the university. And one of my frustrations with the current textbooks or a lot of the textbooks is they basically describe the tree or describe things and they go into quite a bit of detail about the background and individual trees and what they do, what they do, but they don't really explain how they do it or how they function. And so I tried to write and I've been teaching classes on this, and over time I developed my own sort of theory and philosophy about how trees work. And so I put together this small book and I purposely made it a small book, not encyclopedia of fruit production or anything like that, but with the hope that people would pick it up and just pick up the primary concepts, the concepts that I've been working on.

When was your book published?

That's what, that's what the, so the work, the title of the book is Concepts for Understanding Fruit Trees. It's a small book put out by Kathy Press. And the thesis in the book is that while plants, and particularly fruit trees are very complicated organisms, they, there are a few fairly simple concepts to understand, to understand generally what the plants do and how they do it and why they do it.

So.

The primary conflict that I like to get across is that trees and orchards, well, basically any agricultural field, but in our case, where we're dealing with fruit trees. Trees and orchards are basically nature's original solar energy and solar energy, nature's been doing solar energy and capturing solar energy for eons. And when we actually organize our trees or plant our orchards, one of the primary principles that we plant the orchards on is capturing sunlight. So we like to say that we, we, the orchard should be designed so that it captures somewhere between 60 and 80% of the sunlight that hits the ground. And so that's from first principles. Trees are basically solar or our orchards are basically solar rays, solar farm fuel. And the sunlight that, that hits the orchard basically goes into its solar cells. So the chloroplasts within leaves are basically the solar cells of the tree. And from a very simple perspective, the primary function of leaves is the house of solar cells. And this is important because those cells, solar cells can only function if the chloroplasts are floating in essentially liquid. And so the leaves are specifically designed so that the chloroplast housed within, in them can be remain in aqueous solution. And so the, so the leaf is specifically designed to, to display, to be displayed in sunlight and, but also to let in CO2 which is the primary objective of photosynthesis. Take up CO2 and, and give and, but in the process, and it's impossible for the leaf not to give up water because again, the leaf, the, the chloroplast is floating in aqueous solution. And so that means that there's water inside the leaves and you have to have the little valves or gates that let the CO2 in for photosynthesis also let, let water out. So this whole notion that we're going to develop drought resistant plants and, and drought resistant crops and all that sort of thing is this is basically a fundamental problem of physics. Water CO2 going into the leaf is a function of the concentration of CO2 outside the leaf versus CO2 concentration inside a leaf, which is only there's about 420 parts per million outside the leaf and about 250 or so. 220 parts per million depending on what kind of leaf it is inside. So that's the basic gradient that drives the movement of CO2 in versus water. Yeah, drives CO2 in. The big problem agriculture has, especially nowadays as we have water shortages, is that since the stomates are floating in aqueous solution, there's liquid water in the leaf. That's it. Then that gets transferred to a gaseous form and that gaseous form goes out of the stomates when the stomates open up to take CO2 in, and that's about and the ratio, the amount of CO2 molecules are water molecules going out. The CO2 coming in is about 200 to 1. So for every molecule CO2 coming in, you lose 200 molecules of water. So therefore, doing photosynthesis and growing fruit trees is very water consuming. And really, that's a physics, a problem of physics. And we have a lot of molecular biologists and various people saying, well, we're going to fix all this, but biology can't change the laws of physics. And so this is something that we have to deal with. So that's on the that's on the uptake side. So the so trees, basically a tree is structured such that you have these leaves that house the solar cells, and the structure of the tree is basically designed to display those leaves. And so that's what the whole purpose of a tree is all about, basically collecting solar energy and then converting it into carbohydrates. The carbohydrates are then transported around the tree. Now, millions of dollars, billions of dollars have been spent on studying photosynthesis and trying to improve photosynthesis in plants. But nature has done this very well and, and really very little progress has been made. Almost no progress has been made in actually improving photosynthesis of trees or plants. We know a whole lot more about it and why it works and how it works and all the details of the biochemistry and so on. But that's not really helped us improve photosynthesis per se. So then the big problem, the thing that I turned my for about the first eight or 10 years of my career, I was really interested in photosynthesis in the process and all of this in orchards and so on. And but then I realized, and I had a very wise professor once say, don't you realize that the plants are going to do photosynthesis regardless of what you do, is how they use photosynthes. That's the real question. How do the plants use photosynthes? So I turned my attention to that. For the last 25 or so years of my career, we're trying to understand how this decision is made to to distribute the photosynthete that's made or the carbohydrates. Photosynthes are made, another word for carbohydrates, that the plant, which are is basically the currency for growth of plants. And so what determines where the carbohydrates go?

Yeah, Ted, let's we definitely want to get into that conversation, but if I may, I'd like To go back for just a moment to your comments on the billions of dollars that have been spent attempting to improve photosynthesis. And it's my, it is my simplistic understanding that there has been a lot of money spent trying to figure out how to make the process. I'm trying to think of how to describe this, maybe how to make the process different or more efficient, but without seeking to address properly the underlying root causes of the inefficiencies that naturally exists in natural ecosystems. Just as the point that you just made with water, it's pointless to try to produce drought resistant plants because we need water in order for photosynthesis to work well. So if we look at photosynthesis from this perspective, what are the limiting factors in addition to water that you see? Let me back up just a step. It's my perception that photosynthetic efficiency can be significantly improved in different crops simply by addressing a number of foundational pieces really well, like water and adequate carbon dioxide supply in some contexts, some specific nutrients for chlorophyll management and so forth. Do you have any perspective or insights on that?

Well, basically the, from the water standpoint, no, I, I don't. I think people are chasing a sort of a fool's dream because it's a problem of physics. And the only thing that, that that could be improved potentially is the, the reactivity of the stomates to open and close. That is the efficiency of which they open and close. So the stomates have to open in order to let CO2 in. But they, but if they're sluggish, they may not be closing really quickly or opening really quickly at certain times and so on. And people are studying this sort of thing. But, but at the, the primary function problem is that it's, it's a physics, It's a diffusion of CO2 out, CO2 in and diffusion of CO2 out. And those are physical physic problem of physics. And so maybe tightening up and improving the, the photosynthetic idea, the model regulation and some cases might help but, and a lot of people have been working on that whether, whether it's. Whether the plants are actually better off if they're a little bit sluggish and they open, stomates open more quickly or they open more slowly. But at any case you're just barely messing around with the margins in that. Now in terms of the other parts of the photosynthetic efficiency, Rubisco ribiose bisphosphate carboxylase, which is, it's not tremendously efficient. It's the primary enzyme that fixes CO2 or with which CO2 interacts. And. And it's a little bit. The gears slip once in a while or quite often, and so you end up with photorespiration and not real photosynthet photosynthesis. So actually the plants have tried to fix that by. I say try when I'm talking anthropomorphically. They have. There's a mechanism, C4 photosynthesis. Everybody's heard about it. Corn. Corn does C4 photosynthesis. Basically what it is is a little carb. It's a little carbon pump using PEP carboxylase that fixes the CO2 a little more efficiently and pumps the CO2 to the site of ribulose carboxylase. And. And therefore it operates at a little higher efficiency in terms of use of CO2. However, it requires a separate engine. That is the pet carboxylase is the whole set of enzymes and proteins in itself and a little bit of energy involved in doing that and operating that pump. So under high sunlight and a little bit better, or it can be a little more water use efficient because C4 plants, ones that have that little pump in there, they can. The concentration of CO2 in the leaf can be lower down to maybe 100 ppm rather than 250 or 220 ppm. So that makes a gradient from the outside of the leaks on the inside for CO2 a little stronger. So that it. It's a little more efficient in terms of taking up CO2. But there is this cost, a little bit of an energetic cost. And that system works best when the temperatures are above 20 degrees Celsius or 70 degrees Fahrenheit. When you get below 70 degrees Fahrenheit or 20 degrees Celsius, that system is not quite as efficient. And therefore you rarely see a lot of C4 plants where it's cold, where the temperatures are cooler. For that reason and for some reasons, the membranes involved and so on, there's a lot of complications there. But some people are proposing, well, if we just made apple trees or peach trees, C4, that would. That would be better. We would have maybe more efficient. I don't believe that's the case because if you think about it, the majority of the year, even though right now we're experienced in California, 110 degrees Fahrenheit days, the majority of the season, especially the spring season, below 20 degrees Celsius or 70 degrees Fahrenheit in the spring, I mean in the morning and late afternoon and so on. And so it's questionable whether you would actually get, be better off with a C4 plant than a C3 plant in terms of peaches, plums and nectarines and apples.

Yeah, well, thank you for, for entertaining me on that nerdy question. Now let's, let's continue on with the really important topic that you were about to begin on, which is the partitioning of photosynthes. How does, how does the plant decide how it's going to move sugars and carbohydrates around?

Okay, this is the most fun part. The plant doesn't decide anything, so the plants don't make any decisions. The way I look at plants is that the trees, particularly if you think about trees, they're basically multi organismal organisms. That is, each of the organs of the trees basically is semi autonomous. That is, they, they, they have their own control mechanisms within them. They're dependent on the rest of the tree for photosynthes and nutrients. That is, the nutrients are taking up by the roots and the photosynthes are taken up by the leaves. So all the organs of the plant are dependent on that. But in terms of when they grow, how they grow, the rate at which they grow and so on, in my estimation is primarily determined by the organ themselves. That is, there's a. The genetic code of the plant basically has the instructions for how, how individual organs are made and when they grow and when flowering occurs. And my best example of that is what I call the five in one plant, which nurseries in California, some of the nurseries love to produce these, what I call five and one trees. That is a tree that has maybe an early peach, a late peach, a nectarine, an apricot and a plum grafted all on the same rootstock. So when the nurseries like to produce these, they can charge big bucks for them. Growers, I mean, backyard gardeners think, oh, this is wonderful, I can have all five of these fruits and blah, blah, blah. So they go out and plant them. Well, what happens when you plant those trees? Each of the parts, the early nectar and I mean the early peach, the late peach and so on, they, they all bloom according to their own schedule. The tree does not coordinate the blooming and so on. If it's a, if it's a late blooming peach, it's going to bloom late on that tree. If it's early blooming peach, it's going to bloom early on when it's grafted on that stock and the same. And the plums that are on the tree don't magically become peaches. They stay plums. So the, the genetic code, that's when each one of those organs basically clearly is what dictates what the organs are going to do and how it's going to grow and what it's going to be. So that leads me to the conclusion that most all of these parts of the tree are what I call semi autonomous in terms of their, their growth capacity. So then that basically the way I see it is that the tree, all these organs are basically competing for the carbohydrates or nutrients that are taken up by the tree.

That was about to be. My next question is what you're describing is genetic expression of each of these individual cultivars, let's say, is expressing its unique genetic expression. But how does that translate then to carbon partitioning? And you're suggesting that it is through competition.

It's just, it's just, it's just competition. The carbon is. So for years people are saying, well, how does the leaf direct its carbon to the fruit and whatever. I don't think it does. I think the leaf simply. In the leaf, the photosynthete is simply unloaded into the phloem or loaded into the phloem, rather unloaded from the leaf into the phloem. And in the phloem it gets distributed. It, it flows naturally by physical properties, sourcing relationships, that is, that is, higher pressures here and there, munch flow, what we call munch flow hypothesis, sorts of things. And what, what, and what, whatever is able to take it up. The organs that are closest or the organs that are more efficient at unloading photosynthete are the ones that are going to get more of it and the proximity to the leaf. So if you think of the, if you think of the trees, phloem, which is the thing that mainly contribute or distributes the, the carbohydrates within the tree, the phloem are basically the conduit of, for carbohydrates to move. If you think about that as a, as a simple, as a, like a, like a sprinkler system in your yard. When the sprinkler, when, once, when one sprinkler goes on, that's a pressure, that's a, basically a pressure that's pushing the sprinkler to go. But that means that less of that water is going to go to another sprinkler and so on. And if you have lots and lots of sprinklers, the ones that are closest to the, to the source are going to get more water. And so on unless you have excess pressure. But I think in the, in the plant you don't have that excess pressure. So the other thing that we have to keep in mind, which people tend to forget about, is that you have the plants go through a day, night cycle of temperature. So during the, during the day in the summertime, the tops of the trees and the organs in the top of the trees tend to be warmer than the organs than the roots. But at night the roots tend to be warmer than organs at the top. So you have the potential also for, and temperature. The other big deal here is that temperature drives activities of sinks. And so higher temperatures during the day is going to mean that sinks in the top of the tree are going to probably have a better shot. But at night when that temperature is, or that gradient is reversed and so the root activity is going to be relatively higher during the night in the roots than in the top. So this is something that almost no one ever thinks about or talks about. But you have a lot of dynamism in the tree in terms of what these various organs are doing. And then on top of that, the timing of organ growth in trees tends to favor sort of growth of one part over the growth of the other part at different times. For instance, in the spring when you have, when the tree is growing quite quickly, we say that's a grand period of growth you have. Vegetative growth tends to be very rapid and, and this tends to be not occurring at the same time as rapid root growth in many, many plants and the same thing fruit. The maximum growth rate of fruits tends to be in the middle of the summer after the primary grand period of growth in the spring in terms of vegetative growth has already occurred. So you can have this sort of distribution of sink activities over time during the season. Now one of the problems that we like stone fruits, peaches, they're, they're not, I believe, stomach. They're naturally tend to grow fruit more in the middle of the summer and the fruit does then mature later in the summer. And that gives us a chance for the tree to grow its vegetative growth early in the spring. And yeah, there's flowering but relatively slow fruit growth early in the spring and then fast more rapid fruit growth later in the spring. But what we, what we've done is kind of messed that up because now we have very early ripening peach varieties. So you have very rapid growth, fruit growth in the spring over top of vegetative growth. But what's the main characteristic of those fruits? The yield of an Early Maripanic peach will be about a third or a quarter of the yield of a August or September ripening peach. So yields of peaches that are harvested in May or early June maybe are only about 6 to 8 tons per acre, whereas August ripening peaches, you can get up to 32 tons per acre.

So I have, I have two questions. What are there? The first question is are there nutritional management pieces? I'm assuming this determination of carbohydrate partitioning to different organs, first to vegetative growth and then second to fruit later in the season, is partially determined by or largely determined by genetic expression. But are there any factors that influence that can that be managed at all?

That's what, that's what a big part of horticulture is all about, understanding pruning and, and the effects of pruning on stimulating growth and so on. And also fruit thinning. The timing of fruit thinning is very important. It's important to realize that. So the one thing I didn't talk about is that organs also, virtually they grow according to a relative growth rate in general. So relative growth rate is basically in economics, it's a compound interest rate. So a fruit, when it begins, it's growing, it has a very high relative growth rate. It starts the size of a pin, a pinhead, and then, and then it grows. Relative growth rate is very high early in the spring, but over time it levels off and is almost the constant, relatively low relative growth rate over the rest of the season. But what that translates to, because it's a compound interest rate, it's compound, the growth is compounded on the initial size of an organ at any given interval. So if I have a, if I have a fruit that's the size of a ping pong ball versus the size of a pea, and the next, the next interval is going to be a function of that ball versus fall versus, versus the P. It's exactly the same thing as compound interest in the bank. Now the thing is the compound interest rate with fruit growth is declining in the spring. It declines and then levels off. But it's important to realize that if you don't thin your fruit early in the spring, then the size of the fruit that determines the sort of compounding effect for the rest of the season. So, so this is how, yes, all of this business is how is what we concern ourselves with when we're talking about pomology, horticulture, the same thing with pruning. One of the main reasons we prune heavily, peach trees for instance, or nectar trees or Plum trees heavily is to decrease the number of flowers for the following spring. Because if we start out a spring with, if we don't prune and a peach tree, you start out the spring with 10,000 flowers. When you can only, when you can only carry 500 fruit on a tree, there's no need to have those 10,000 flowers. And the sooner you, you decrease that 10,000 flowers down to 2,000 flowers and you do this by pruning in the spring now you only have 2,000 fruit that are left on the tree are potential fruit that's still too many. And then in the spring you have to thin those down to the 500.

Yeah. So one of the questions I've had this observation for over the last dozen or more years that in many cases the highest yielding crops are not the crops that have the most vegetative growth. And this was also true for, and this is across a number of different crop species, not even just trees.

Where.

There was this idea of a required leaf index that we need to have a certain number of certain leaf surface area. And it's been my hypothesis that actually what matters more than total crop leaf index is the size of the leaves and the total leaf index with the, for some of these crops with fruit associated leaves. So spur leaves, for example, in the case of spur bearing fruit and that that has perhaps more of an impact on overall fruit quality and harvest than the overall leaf index. Can you offer some insights and perspective on that?

Yeah, absolutely. So there's a lot of people that are talking about, or traditionally in palmology they say that this leaf to fruit ratio a certain number of leaves per fruit and so on. That's okay, that's sort of the general concept. But not all leaves are going to be equally exposed. And so if you have a very dense canopy you're going to, many of those leaves are, are fairly inefficient. And so I, I, I've really never liked that very much. I prefer to think of total light interception of a tree and then having, but also the goal of the grower is to have well distributed fruit and, and, and fruit distributed in, in areas where there's light. Now the big problem, the big problem we have with trees is that they weren't, they weren't original design, originally designed to be orchard in orchards. Very true. They were originally designed to put up with nature. And one of the big issues that nature brings is either limb breakage or browsing or ice storm or something like that. Trees are geared to take an occupy space, occupy area like the Difference between a tree and an annual plant like wheat plant or arabidopsis, the ultimate annual plant. Those plants are designed to have the seed germinate. The plant grows very rapidly and reproduces immediately. And so within, within either three weeks or six months, the entire life cycle of the plants is done. Now trees are on the opposite end of the spectrum. Trees are designed to. The seed germinates, the plant grows and the plant occupies space. So first it occupies space. In the case of trees, it's both space laterally but also vertically. And so and then, and they, most trees have a juvenile period where they don't reproduce at all for the first 2 to 5 to 10, 15 years. Most of our fruit trees, it's basically between 2 and 10 years juvenile period. But that juvenile period allows the plant to put all of its effort into growing vegetatively and occupying that space. And the plant then is geared to occupy that space. So the plant then has a built in fail safe mechanism. What happens if you have an ice storm or something that breaks all the branches, the, the plants, the, the trees adaptation of that is to grow what we call suckers or water sprouts. And these are, these are rapidly growing shoots that will grow the entire season long. And in case of, in case of an ice storm or something that breaks the tree down, the tree uses the resources that are in the roots and in the lower part of the tree to rebuild that entire tree again as fast as possible to reoccupy the space at once occupied. Now this is a built in mechanism. So you have these three different, you have a different kind of shoot. We call these water sprouts or epicormic shoots. And they, they have the ability to start growing and continue growing an entire season. Whereas the other shoots on a tree, the normal shoots, the shoots that grow out of lateral buds in a normal springtime, they're called proleptic shoots. And they typically only in peaches, they only grow a maximum of 33 nodes and many, in many trees, they, they only grow for the first two months in spring and then they're done. But these empicormic shoots or water sprouts cause the grower a problem. That is, it would be somewhat better for the, for the grower if they could somehow shut off the epicormic shoots and get. Now you get. We're getting back to the question you had a while ago. That is, that is, it's not necessarily the most big investment growth that gives you the most yield. In fact, one would, would argue that if we could shut off Epicormic growth or those water sprouts, if we could shut off those after the tree is full size, we would be much better off because really all you want is the fruit and shoots, the spurs and the short shoots fruiting to supply your photo and to carry your fruit wood and so on. But those water shoots are a natural phenomenon. And when growers use heading cuts, heavy heading cuts like topping or heavy pruning, cutting into two and three year old wood that stimulates the water sprouts and basically that's a, that's a wasteful cycle.

As you've been describing this process. My, my mind has been going back to what you described around the, the 24 hour circadian rhythm of and the temperature differential of how sugars or how organs grow and utilize sugars dependent on temperature. And that determines sugar flow throughout the various parts of the plant to the upper aerial parts of the plant or to the root system. What are the management implications for growing trees or just plants generally, but trees in particular perhaps at higher elevations where you have more rapid temperature swings during the day and nighttime temperatures versus, versus not there.

There are implications there and it hasn't been a whole lot of research, but we know that grow apples grown. One of the problems that the Netherlands has with apples is the apples tend to grow too big. This is because. And part of that reason is for some varieties, part of that reason is because their day lengths are longer and their temperatures are cooler on general. So the temperatures are rarely get above. 85 degrees maybe and so that, so respiration is not excessive but yet photosynthesis can carry on very well and it's for 16 to 18 hours a day. So latitude, so latitude can have a significant effect on, on fruit size and yields and so on. And I think, although I'm not sure, I'm not 100% my guess is the reason why you get very large cherries coming out of Canada toward the mid middle of the year, these huge cherries that come out of British Columbia and so on. I think it's because they have long day lengths and not such high temperatures and you get into the latitudes in Mexico. I, I've talked to growers, peach growers there in Mexico, they have a very hard time getting fruit size and peaches and I think it's because of their high respiratory rates.

So so far in our conversation, Ted, we've been having this discussion around principles and understanding the principles behind how trees work, which I think is so fundamentally important. But can you give us an example of what this looks like in actual practice, when we keep these, when we keep these principles in mind, how does that reflect itself in practice? How do we begin managing pruning differently or managing a tree differently as a reflection of understanding these practices well, or these principles well?

So in pruning, in terms of pruning, it would be largely understanding what drives the development of the epicormic shoots. That is, and going in and pruning, you can, if you go in and if you do heavy pruning everywhere, you're gonna, everywhere you're, where you cut into 2, 3, 4 year old wood and do a heading cut, you're going to stimulate a water sprout. Now, sometimes that's unavoidable, but what I would recommend then is going out in the springtime when the water sprouts become apparent, when they're only 12 to 16 inches long, and just pulling them out, don't prune them out, just pull them out. And you recognize that those are water sprouts, they're going to be that way and you're better off getting rid of them. And you can you treat those differently than you do your normal fruiting shoots, the normal ones that come out of buds from the previous season. So basically, water sprouts come out of what I call preventitious meristems. There it is. So, so what I teach in my classes, that is that you have two types of shoots growing, well, actually three types of shoots, but basically shoots that grow out of preformed buds. Those are your normal, normal fruiting shoots that are only grow to a certain length, but you also have fruits, peper, Cornish shoots, which grow out of their preventitious meristems that are buried in the wood at each node along the plant. And so if you understand, okay, I'm going to prune that hard, but I'm going to have to put up with that shoot coming. Then you have to deal with that shoot the problem spring, and you can deal with those separately. So, but understanding that basic thing is important, also understanding that by doing these hard heading cuts. So traditionally in California, we've had, we have the system. When you grow a tree, you grow it up and you do a hard heading cut in order to stimulate strong vegetative growth. The strong growth you're stimulating are the epicormic shoots. And so if you recognize, oh, in that hard pruning, I'm stimulating the leftover shoot that you, you, you can alter the way you prune, say, wait a minute, I'll leave that, and do thinning cuts on it rather than a hard heading, it's going to stimulate something to regrow. So if you understand what's stimulating which kind of sheep to grow, you can adjust how hard you prune and, and what, what shoots you do. Similarly, the principle of relative growth rate for fruit tells you inherently that the earlier that you thin the fruit, the earlier you thin the fruit and you get the number of fruit that, that the tree is going to carry through to harvest. The earlier you can get that done, the better off you are. So, so in terms of practically, what happens is we now have a we have mechanisms to do flower, flower bud reduction mechanically, and there's thinning. Thinning by doing that is never going to be precise. But if you can reduce that initial flower load from 10,000 flowers to 2,000 flowers, and mechanically, then following that up with a hand thinning later on is going to be a lot cheaper than if you're after thin. So each one of these sort of understandings of principles lead to better horticultural practices.

TED I haven't been asking many questions in this conversation because you've been anticipating every question. I was just about ready to ask you about fruit thinning, but I think the next question that comes to mind following fruit thinning is considering it's wiser to thin fruit earlier rather than later, as early as possible, because we're then not in essence, wasting the tree's energy. How does this translate to the idea of summer pruning versus dormant season pruning and pruning vegetative growth? Are we also better to prune vegetative growth earlier rather than later?

In a lot of senses, yes, especially. So there's two types of summer pruning, one that I would always recommend, and that is summer pruning to eliminate the, the water sprouts or to get, to get, to get those paired down to just a few, because those water sprouts are just going to grow very strong. They're not going they basically don't provide much energy back into the tree. They basically use up the energy to grow for the rest of the season. But in the meantime, they're also sitting on the top of the tree, so shading out the leaves that are feeding your fruit. So summer pruning water sprouts and doing it early I think is a really good practice and it could be done relatively efficiently. Now, some are pruning to select fruiting wood and all that sort of stuff, like in some crops like cherries and apricots, where we don't like to prune in the wintertime because of disease problems. We have shoot disease problems. If you do pruning cuts, have exposed pruning cuts in California in apricots and cherries, we prefer to prune those. That is, you're pruning even the fruiting wood right after harvest, but during summer. So those are two different kinds of pruning. And so, but again, understanding the different kinds of shoot growth and what each type of shoot growth is doing and so forth is it really helps you to improve your management practices.

Ted, as you've developed your understanding of carbohydrate partitioning and these various tree organs expressing themselves differently, how has that, how, how has that growing understanding reflected itself in changing management practices? Or maybe a better question to ask is with, with this foundation of really understanding trees, what are some of the common mistakes that you see growers making in unintentionally mismanaging their trees for less than optimal health?

Well, so I haven't really talked about nutrients, much nitrogen and so on in California. Now, nitrogen in the groundwater and all of that's really important. And we've come to realize that nitrogen uptake also by the tree is primarily when there's leaves on the tree and there's activity. And so managing our fertilizer regimes, we've gone to more where we fertilize primarily in the spring, but in small doses, when the tree's growing and when the fruit is is growing, like in almonds, it's recommended you do basically what we call spoon feeding. So if you can fertigate, putting fertilizer, fertilizer through the irrigation system, that you can spread that fertilizing out to the periods when the tree is primarily growing and when the fruit is primarily growing. And we in the old days, when I first started this, I would say most of the nitrogen was applied in the middle in the winter time, assuming that the nitrogen is going to stay in the soil available for the tree the following spring. And now we realize that, well, a lot of that nitrate goes down to the groundwater and doesn't stay. So now the recommendation and that trees don't take up nitrogen during the wintertime. So all of this has led to a much more efficient nitrogen fertilization practices, I think. And, and they're actually policies put in place now now in terms of managing orchards, fruit, certainly fruit thinning, timing of fruit thinning and so on. One of the things that I got involved in early on was that California here, the cling peach growers, and they still do it, which is kind of ridiculous, is that they wait until what they call Reference state to thin. So reference date is 10 days after PIT hardening by definition. So what they do is they cruise field and they begin, begin with a razor blade cutting back from the fruit back until they hit the pit. And if they get resistance on the pit or the pit is hardening, they say that's pit hardening. So we're going to wait 10 days and after that they begin thinning. So the notion for this was that they would do this and it's, and it was an industry ride recommendation. They would do this because you would get fruit drop. You potentially could have June drop. That is a natural fruit drop occurring before that date. And also if you thin before that date, you would tend to stimulate sweat thrs. Well, we start after we started studying fruit growth and the relative growth rate concept and so on. We said this makes absolutely no sense. So we made, we did several experiments two different years where we thinned down fruit in early April. One treatment and we waited until reference date and the other treatment and we gained as much as 8 tons per acre yield when we did the early thinning versus late thinning. And we had, we didn't have any more split kits. And we did this on four different cultivars in two different years in two different orders, both the north and south part. Yeah, so they did the ones in the south where they grow fresh market fruit. They tended, their practices tended to change and they thinned much earlier. But I still see north. It was too big a leap and they, they still don't do it necessarily now. Actually we've had a huge turnover of orchard managers even in the fresh fruit in California because we've had a lot of large operations going out of business, kind of bankrupt and so forth.

And.

So, so a lot of their understanding is no longer there. And, and people have been, we've been noticing people resorting back to old things because it's much cheaper to thin. When the fruit is bigger, the result is much poorer. But it's a lot, it's a lot cheaper. So if people don't, you've actually seen sort of retrograding of expertise in the stone and crude industry in recent years because of the huge turnover in management.

Yeah, that's unfortunate. And it's also, it's also a significant opportunity for the better managed orchards to excel and to excel into the future.

Yeah. Yep.

So, Ted, I really loved your book Concepts for Understanding Fruit Trees for all of our listeners. I'll include a link to it in the show notes. I also wrote a short piece about it on A blog post recently. What are the key pieces you would like for people to know about your.

Book that is not meant to be an exhaustive homology text, but it's meant to give them a fundamental understanding of how trees work and my concepts in terms of how trees work. And if anybody's interested, I still teach extension class every year in the spring at UC Davis. I teach it along with several other people and it's basically called the Print Port class. And it's open to people, anyone around the world to take the class and they for information if they want to see it, if they want. Sorry, if they want to. Information on the class go through the Fruit Nut Research and Information Center, UC Davis. That's fnric.

Wonderful. Well, thank you, Ted. Thank you for all of your thought and research over the years, all the work that you've put into this, and for sharing it so freely with everyone. I really appreciate the work that you're doing.

Yep, sure. My pleasure. And if people are interested in any of my research, they can go to tmdavis. Edu and look at for my website. I have a lot of my publications.

The website Wonderful. We'll include links to all of those.

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