But what does it do? Copper toxicity, that is.
If a nutrient gets too out of balance in the soil, it can become toxic to the plant and/or block the uptake of other nutrients. I’m not sure what the symptoms of soil copper toxicity are in fruit trees, but it can happen. According to this book, copper toxicity occurs when there is too much copper in the soil to begin with, or too many Bordeaux sprays.
Too much copper is also toxic to earthworms, and probably a good many other living things in the soil. It can also be toxic to fish.
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Bacterial spot is a pretty big issue with stonefruit in the humid regions as is peach leaf curl. Copper can be the ticket and I’ve never heard of even a commercial grower suffering serious consequences from excessive copper apps. Have you? The question is serious and I’m genuinely curious. Bordeax sprays may be an historic example of “copper gone bad” or may just be an anecdote passed around as so often happens in horticulture.
In my experience the worst spraying calamities have come from hort oil- either applied when it’s too hot or too cold or just during very poor drying conditions.
Of course, he shouldn’t include copper if he isn’t targeting an identified pest with it.
Here is a very comprehensive article about potential dangers of excessive copper app. I have some doubt if a single application annually to fruit trees poses a risk to normal soils with near neutral pH, but I’m only speculating.
https://link.springer.com/article/10.1007/s13593-018-0503-9.
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Timely thread. I generally don’t spray, but my little Seckel pear had blister mites pretty bad this past year, and its first real crop. I’m looking at dormant oil and copper. I’d do lime sulfur if I had it, but don’t and aren’t ready to jump right to off label.
The weather is clear, calm and the sky is mostly blue right now. Might even not rain for a few days.
I’m looking at 1 tablespoon of 8% copper (either Liqui-Cop or Kor-R-Spray) per gallon and 5 tablespoons of dormant oil per gallon. I’ve had the copper for a while without using it, will see if one looks better than the other.
Will go on pear, plum, pluot quince - we’ll see. I have a 4 gallon diaphragm pump I bought years ago and have yet to use.
Good luck, Murky. I tried copper on pear blister mites. Not working. Lime-sulfer has worked. Other said even just sulfur work for them at a bud break stage, not dormant.
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I have some sulfur. If I can psyche myself up, I may spray it in a couple of weeks from the oil.
Spraying is a pain, I can se why I haven’t bee doing it :). Doesn’t help that every tree is on its own schedule, several of them, more than one.
It will be interesting to see if I’ve caused any harm, and if I notice any difference, to any of my trees, that I can attribute to spraying.
I’ve also got to look into some better PPE if I’m going to make a habit of this. I used a KN95 mask and some foggy goggles, a long sleeve shirt, nitrile gloves, and a beanie for my bald head. It was hard to see what I was doing and I got sweaty out there in the sweltering 58 degree sun.
P.S. I’ve got tons of respect for real farmers and orchardists. I’m not cut out for it.
****“Historically, the most commonly used fungicides available to home gardeners have been the fixed copper products. For all copper-containing products, the active ingredient, copper, is listed as “metallic copper equivalent,” or MCE, on the label. Various product formulations differ widely in their metallic copper content. The higher the MCE, the greater the amount of copper and the more effective the product will be.”**from ipm.ucanr.edu
A fixed copper product, like Kocide (copper hydroxide), contain 30% elemental copper. As you stated, copper ammonium products, like Liquid-Cop and Cop-R-Spray, contain 8% elemental copper.
This year I’m alternating Kocide with Lime/Sulfur to battle last year’s really gross case of pear blister mite.
I did a search today about copper toxicity and fruit trees, and basically found nothing. I suspect it isn’t much of a problem even on a commercial scale.
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Thanks for the info. Some good facts and data.
Copper in soil may be toxic to plants (phytotoxic) at levels below those that are a concern for human health. At levels above 75-100 ppm in soil, copper can cause toxicity and stunted growth in some crops. This is more likely to be a concern if pH is low. http://cwmi.css.cornell.edu/Metals_Urban_Garden_Soils.pdf
In my latest soil test, Copper was 4.1 ppm. According to the analysis, that was considered “very high” I’m interested in others’ Copper results from a soil test.
But apparently very far from high enough to produce consequences. That suggests that if would be quite difficult to drive up rates in the soil to levels 20X higher than what is already considered “very high”.
It usually isn’t difficult to bring up the pH in soils to the approximate 6.5 considered ideal for most tree fruit.
My copper level on my soil test from last year was 15.76 ppm. I have never applied any copper. Ph 7.3 I would suspect that with the cdamarjian soil test, where it referred to 4.1ppm being very high was from a plant need aspect, not a toxicity perspective.
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Interesting comparison. The pH of my sample was 6.6. Perhaps lower pH means greater copper solubility and more leaching (diluting?) of copper in soil. ??
Will do another test right under drip line of peach trees, which have been receiving homemade Bordeaux mixture for 15 years. Compared with my baseline, that would better indicate the cumulative effect of copper application. Love the chemistry of botany!
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Some really great information here around copper and the toxicity. My old extension office made it sound like regularly using copper would kill the worms and other beneficial ground dwelling insects. It looks like pubmed.gov is saying similar to Cornel, around 100ppm for being lethal to earthworms. Looks like I will bring this back into my regular arsenal if needed.
As mentioned Kocide 3000 contains 30% actual copper. With one annual leaf curl spray for peaches, that adds about 1.5 ppm per year. Assuming zero initial copper in the soil (everyone’s soil is going to be different) it would take 50 years to reach the 75ppm threshold mentioned earlier.
According the link Alan posted Cu apparently doesn’t leach out of the soil profile very easily, in most soils.
“In most soils, Cu residues are likely to remain indefinitely and will continue to influence the health of the soil (Van Zwieten et al. 2004).”
Copper is obviously not going to a problem with an annual application in a backyard orchard. I suspect where they’ve seen problems of toxicity to plants are with repeated applications throughout the season (i.e. citrus orchards) or orchards which have been farmed for generations.
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These statements worries me.
Thats a nasty combination. 50 years to reach a treshhold that stays indefinitly 0_0
Lets look at nucleair power. (unarium based, not talking about deuterium fusion)
There is a natural background radiation everywhere. Mainly from sediment rocks but also concrete. see https://www.cdc.gov/nceh/radiation/building.html#:~:text=Radioactive%20materials%20in%20sandstone%2C%20concrete,into%20the%20radioactive%20gas%20radon. for example.
There are “acceptable” levels specified in most countries.
In theory you could spread out (dillute) your radioactive waste over an large enough area to stay within the acceptable levels. Still this does not seem like a good idea to me.
Mainly because of 2 reasons
1- because it stays there for multiple generations. You should not only take into account how much damage it does to yourself today. But also how much damage it will do to the people and organisems after you’r no longer here. (always try to leave a place “nicer” then you found it!)
2- just because something is withing acceptable levels and you don’t see immediate damage. Does not mean there is no damage at all or no damage will occur long term.
Especially if you combine these 2 factors.
A short half life herbicide that will lower crop yield bij 50% seems extreme compared to something that only lowers crop yield by 1%. However if those 50% yield reductions dissapear after 2 years, and the 1% reduction goes on for millenia. Suddenly the picture changes.
I see copper the same way.
What does this mean practically.
Will i ever use Copper. Yes probably, if the short term consequences are that dire that i don’t really have a choice. (just like with nucleair uranium power)
Should i use it when there is a sufficient alternative. Hell no.
Using copper once or twice, probably won’t spell disaster. You will probably never notice. But still it has really long term consequences. So keep those in mind. (in short, don’t be selfish 
)
-only use it when you have to. (if your loosing 100% crop i can imagine you have no choice)
-only use it on the species that absolutly need it. (if your stonefruit dies without. but your apples “only” loose 5% crop. Consider only using copper for stonefruit. )
-don’t use “left overs” just for the sake of it. If you sprayed enough, don’t spray more.
-don’t just dump left overs, try and make no more then needed. And try to properly dispose of leftovers. You could also try and compensate for your copper use. By taking extra care to recycle/repair electrical appliances and just taking care of the planet.
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This discussion has made me rethink my initial sanguine take on copper use in my own soil. I’ve been using a copper soap to reduce early blight on tomatoes and will apply it about 4 times on a weekly basis early in the season, stopping after tomatoes have been formed to the point of representing a crop.
If I don’t spray, my crop will be reduced quite a bit, but I’m thinking the better environmental approach is to use a couple of chlorothalonil sprays instead. Smaller harvests is more than inconvenient- it also represents bad ecological land management to me. Better to use less land and leave other fallow and in nature.
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I need to make a correction. I miscalculated the amount of copper above. I stated one application for leaf curl raises the copper 1.5 ppm in soil. That’s incorrect. One application adds 1.5 lbs. of copper per acre, but only increases the ppm by 0.375 ppm. So to get the 75 ppm, it would take not 50 years, but more like 200 years. Sorry for the error, and the resultant direction it took the thread.
As an interesting aside, Surround is a much more serious issue for soil contamination, imo. I don’t get very excited when I hear of commercial growers using Surround so they can be organic. Surround is about 5.5% aluminum, by mass.
That’s not a high percentage, but the huge amounts required on a per acre basis puts a significant amount of aluminum in the soil. For most crops 50 lbs./acre per application rate. It puts 2.75 lbs. of aluminum per acre on the soil. That’s still only about 0.68 ppm, but repeated applications are generally required throughout the season. With 3 seasonal applications, one increases the Al by 2 ppm.
I’ve never heard any concern of this, so maybe Al leaches out of the soil more easily than copper, but I doubt it. Or it may be that it’s so new (relatively speaking) that no one has seen toxic levels of Al in their soils yet.
Again, for a backyard grower with a few trees, it probably doesn’t make much difference, but for a commercial grower, they could possibly ruin a lot of land, in their lifetime.
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I either have missed part of discussion or you guy missed the part of fact that minerals recycle naturally by the trees/plants.
I understand the copper build up in the soil is a bad thing. But copper as one of plant essential minerals, isn’t it consumed by plants , stay in the roots, supply to the leafs which will be blow away by wind or cleaned up and hauled away in the fall? While we do plus on the copper ppm in the soil by copper spray, haven’t we thought of do minus on plant obsorbing the copper from the soil?
I see some plant foods contain copper, so it can’t be all bad.