This video discusses Leaf Brix relationship with insect resistance, summarized in the chart below.
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This chart does not apply to several genre of fruit trees nor to a number of pests in each of the listed groups for any genre of fruit tree.
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To which fruit tree types do you think the chart would apply? I would think the presenter meant the chart to be rule of thumb for common fruit trees and pests. The presenter is from East Coast (FL / NY) so perhaps he’s more familiar with pests there.
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The video is interesting. And I’m sure there’s a lot of truth in there. But if it’s all true then east coast fruit growers should be able to grow high brix fruit via proper nutrition. And that doesn’t seem to be the case. It also doesn’t explain how I grow high brix fruit on poor low organic soil with basically no fertilization.
No mention of the role of water in fruit tree brix. Lowering water level in the tree is the way that I’ve seen to increase brix. Deficit irrigation, ie a controlled water deficit, clearly increases fruit brix and I’d bet also leaf brix.
@alan take on this would be interesting. Sorry the video is 55 minutes.
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One way i select seedling fruits is by how damaged the leaves are in relation to the other seedlings. What i have found is the plant with the highest sugar is the highest target in the presence of insects. All that means is insects like people go for the highest calories in my belief. Provided we are talking about apples insects , people and animals consume them. Insects correct anything out of balance. Insects avoid pawpaw " Pawpaw fruit contains high concentrations of annonacin, which is toxic to nerve cells . In addition there have been case reports of possibly related nerve toxicity. Therefore, chronic use should be avoided."
American pawpaw. I’m merely pointing out pawpaw are very high in sugar.
" * Toxicity caused by two compounds, oxalic acid and caramboxin
- Oxalic acid, a vitamin C metabolite, can worsen renal function but does not cause neurotoxicity
- Caramboxin, an amino acid neurotoxin, stimulates glutamate receptors, which leads to seizures[1]"
“Although no specific mention has been seen for this species, it belongs to a genus where most, if not all members of the genus produce hydrogen cyanide, a poison that gives almonds their characteristic flavour. This toxin is found mainly in the leaves and seed and is readily detected by its bitter taste. It is usually present in too small a quantity to do any harm but any very bitter seed or fruit should not be eaten. In small quantities, hydrogen cyanide has been shown to stimulate respiration and improve digestion, it is also claimed to be of benefit in the treatment of cancer. In excess, however, it can cause respiratory failure and even death.”
I readily consume all 3 of these plants but insects and even many animals will not partake. Sugar content is often high in these fruits. There are many other sugary somewhat toxic plants. One indicator for me a person has a disease or illness is by how the insects behave around them. A friend was heavily mosquito attacked when we were fishing. I asked if he had diabetes and he said no. He was hospitalized for heart and diabetes within a year. A close friend was attacked heavily by chiggers and died a few years later from cancer. Neither the mosquitos or chiggers bothered me. Does sugar play a role in cancer, diabetes and other disease? Are the insects and animals telling us something other than what we realize they are?
Im not suggesting natural sugars are processed sugars. There is a correlation between excess sugar and disease.
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I’m always skeptical when I see information presented by folks who are promoting the sale of something
In this case it’s a $250 course in fruit tree care or perhaps $150 for a “Fruit Tree Pruning Masterclass”
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I agree. And he’s apparently recommending various fertilizers and who knows what else. Plus he’s offering his services to growers at I’m sure a hefty fee.
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There’s many things that were said in the video. This is my summary of his arguments.
Trees
- Sugar is the main product of photosynthesis
- The healthier the tree, the more sugar is in leaves (leaf brix)
- If a deficiency was fulfilled, leaf brix will raise when measured before/after
Insects
- Sufficient amount of leaf brix interferes with insect digestion
- Aphids (and scale) have simple digestive system aren’t particularly looking for sugar but rather nitrogenous compounds. They excrete much of the sugar out as honeydew. Tolerates lower leaf bix only.
- Larger Sap suckers (leaf hopper, stinkbug, lanternbug) have more complex digestive systems and can tolerate higher leaf brix than aphids
- Chewers (grasshoppers, JBs) have the most complex digestive system and can tolerate highest leaf brix
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There are many factors that cause it not to be that simple. As an example a deformed tomato is healthier than a perfect tomato off the same plant. More water = less sugars. @fruitnut shorts his fruits water increasing the brix. Have done so myself during a drought not intentionally. The results of less water are always sweeter fruit.
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Thank you for the summary. I did intend to question the validity of research produced by the PHD Entomologist. Very interesting research that could perhaps allow growers to produce the same quality fruit with fewer synthetic chemicals.
My comments were directed to the organization selling their fruit growing and pruning manuals for very high prices. I took a quick look at their website with the $249 fruit tree care course and chuckled
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That’s not necessarily true. Plants need water to photosynthesize and make sugar. If your plants are severely water-stressed and start losing leaves before fruit maturity, you are compromising the plant’s ability to produce and transport sugar to the fruit. Water stress can also cause plants to close their stomata to prevent water loss. Closed stomata = no CO2 uptake = no sugar produced. And for some fruits like grapes, water stress or extreme heat during ripening can cause sugars to increase due to water loss from the fruit, the end result being higher Brix but lower yield and sometimes fruit that has too much sugar while still tasting underripe.
For wine grape growers here in California, late summer becomes a struggle between irrigating enough to maintain a full canopy of leaves to ripen the fruit and prevent losses due to dehydration and sunburn and giving the vines enough water stress for optimal flavor and fruit quality.
I’ll admit I don’t remember my plant physiology courses super well, but from what I understand of plants and source-sink relationships, correlating leaf brix with plant health seems like an oversimplification that doesn’t take into account where the sugar in a plant is going. Leaves are factories that make a product (sugar) that is exported to downstream consumers, whether that is for metabolism or storage. For the most part, fully mature leaves use little of the sugars they produce. Instead, those sugars are transported to sinks; i.e. flowers, fruit, carbohydrate storage, and new growth. In fact, increased leaf sugar can mean that something is wrong with the transport system. Girdling a branch (and preventing photosynthates from moving into the rest of the tree) increases leaf brix. Some pathogens like viruses and phytoplasma cause an increase in leaf sugar levels at the expense of fruit sugar. And like a human factory, leaves have regulatory systems in place that lower production when demand is low. Several key genes involved in photosynthesis are downregulated when sugar levels increase. Most of the papers I could find that studied leaf sugar levels in relation to insect pests were looking at herbaceous forage crops, which have a very different carbohydrate assimilation process than fruit trees.
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All true and especially important for commercial production. From what I know and saw when I lived in CA, commercial growers there aren’t interested in a water deficit to increase fruit brix. They’re interested in yield and other factors associated with shipping and selling fruit. Plus, in CA in summer it’s so hot and dry that there is some water deficit by default. At least in comparison to eastern US growing conditions.
I thought that CA fruit, mostly stone fruit, bought at grocery stores and farmers markets was subpar. I can still remember the first bite of a really superb nectarine at a DWN fruit tasting in Reedley CA. I wasn’t able to duplicate that until I figured out deficit irrigation in my greenhouse here in west Texas.
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There is oversimplification and generalization where it fits the hypothesis, the facts are cherry-picked.
The definition of “healthy plant” on which these claims are based is questionable, indeed wrong. That insects do not attack healthy plants is simply not true.
Also, it’s not a new idea; this 1996 paper refutes such hypotheses, finding no correlation between brix/leafhopper population:
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Also, it’s not a new idea; this 1996 paper refutes such hypotheses, finding no correlation between brix/leafhopper population
Nice addition, @no07
That data looks pretty good to me. I think it’s fairly convincing- there does not seem to be a strong relationship between leaf Brix and leafhopper pressure, at least in grapes.
@no07 Thanks for providing that study. I read it and thought about it. My criticism of the study “Leaf sap brix and leafhoppers in vineyards” is that data is averaged per date, so we have no idea of the relationship between leaf brix and leafhopper density on one particular day at a particular site. The data could be compared against sites for a particular day, but the leafhoppers can’t chose the site, so it doesn’t appear a fair comparison. To me at an intuitive level, nature is about outrunning the other guy being chased by the bear. The way the data was averaged and presented, unfortunately eliminated all trace of selection done by insects pests.
Thanks for everyone’s input, I’m learning a lot.
@sockworth Thats not quite how I’m reading it. Looks like each figure is showing data from a single plot/vineyard and each data point is an average of 20 leaves. Would be nice to see as a boxplot rather than average per time point, but I think the average isn’t necessarily a bad measure.
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There is a point where a line is crossed making less water no longer desirable thats true!
Yes each data point is an average of readings at a particular date. Since the leafhoppers can’t jump through time or from one orchard to the next, you can’t see the selection done by the leafhoppers since the data is lost in the averaging.
I took about 10mins to read it, it’s possible I missed something.
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