What does copper do to fruit trees exactly?

Like any fruit grower I’m cautious what I apply to fruit trees and copper is a great friend and can be a bad enemy. See this article http://homeguides.sfgate.com/effects-copper-sulfate-plants-27633.html

“Soil Enrichment
Used in an area of copper-deficient soil, copper sulfate enriches the soil and provides an essential nutrient to growing plants. When soil is copper-deficient, young plants may develop chlorosis, a condition in which leaves yellow due to lack of chlorophyll. Copper deficiencies can also cause stunted or atypical growth; young plants in very nutrient-deficient soil may simply die. Wilting, lack of flowers and reduced fruit harvest are all likely effects of copper-deficient soil. Copper sulfate prevents these problems. Test soil regularly, and apply copper sulfate as needed in a spray or fertilizer preparation.
Fungus Protection
Copper sulfate has anti-fungal properties, and is a key ingredient in some commercial fungicides for farm and garden. These fungicides are typically mixed with water and either lime or soda ash, then sprayed onto the plants. The effect of such a copper sulfate fungicide is prevention or reduction of fungal infections that can disease or destroy the plant. If a plant is already affected by fungus, copper sulfate fungicides may be effective in removing the fungus. This use is effective only if the fungicide is applied soon after fungal infection occurs.
When copper sulfate is applied excessively, soil copper levels become toxic to plants. Plants growing in soil that has too much copper may develop discolored leaves as a result of iron chlorosis. Typically, leaves will become dark green, then turn white as chlorophyll fails to enable proper photosynthesis. Additionally, copper toxicity can cause damage to the roots of plants. When roots are damaged, plants are likely to grow more slowly, wilt or even die.
Effects on Fruit
In fruiting plants, copper affects the sugar content and flavor of the fruits produced. The effects of copper sulfate are most pronounced in blueberry, tomato, watermelon, onion, parsnip, lettuce, beet, carrot, cabbage, eggplant, celery and spinach plants. In general, water accumulation in a plant is lower, and therefore its taste is sweeter, when its conductivity is low. Excess copper sulfate increases conductivity, reducing the sugar concentration and flavor intensity of the fruit. If you want to grow sweet fruits that are not watery, ensure you are not over-applying copper sulfate to your plants.”
Copper is not a cure all. What has been your experience with copper?

I found this article to be of interest in better explaining the mechanism of how copper works:


From what I got out of the article, certain formulations of copper have low solubility in water, so what you’re spraying on your plants is essentially the copper in a suspension (as opposed to a solution.). The copper dries onto the plant. Now, the important thing to remember is that copper has LOW solubility in water, not 0 solubility. So each time, a certain amount of the copper becomes copper ions in the water. These copper ions are able to denature proteins, and since every cell depends on proteins for cell functions (including reproduction), this denaturing kills the pathogen.

And every time it rains, more copper ions are released.

What I found interesting was that water with an acidic ph dissolves much more copper into solution–leading to an increased chance of phytotoxicity. So, it would probably behoove the grower to spray the copper on when the water is as close to neutral as possible in order to lessen the chances for phytotoxicity.

Perhaps the is common knowledge, but I did not know this.

I guess it’s a case of the dose makes the poison. Just the right amount, and the copper kills the pathogens. Too much and the copper kills the pathogen and the plant.

Sorry if nobody else is interested in the kind of thing, but I always find I understand things better when I know the reasons why.


I knew water was a factor with sprays because many growers reduce the ph of their water by adding vinegar for the reasons you mentioned. Once spray is mixed with water you want to apply it asap. I did not think about coppers relationship to water though it’s obvious now that you brought it up. Thanks for bringing that up because I’m the type who would have eventually tried to lower my copper use by decreasing the water ph. You prevented a problem for me I would have eventually had to deal with.

In my area, Copper Hydroxide is normally used by commercial fruit growers rather than copper sulfate alone. Copper Hydroxide does not release all of the copper ions at once which makes it safer for the tree and the fruit. Copper sulfate (bluestone) is often mixed with lime to make Bordeaux mix which has been used on grapes for hundreds of years.

Copper hydroxide or sulfate are essentially biocides with the potential to kill green tissue on the trees. The dose and the timing are very important. The proper dosage is provided by the MCE number. Each copper product has a different MCE . I use Koicide 3000 where each pound of product is the same as .3 pounds of metallic copper (MCE). I just sprayed my apple trees where the suggestion was for 2.5# MCE per acre around 1/4 inch green. I mix copper with oil which works well and saves an extra spray. If I spray too far past 1/4 inch green, I run the risk of russet on my apples. The same concepts apply to peaches but copper for peaches is often sprayed again at a very reduced rate at petal fall or even shuck split.

Check out the link below from Penn State for the best info on the use of copper on fruit trees that I have seen.


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copper is murderous to microbes/fungi. And in some applications, extremely durable and only gets ‘consumed’ by friction.


There has been a lot of recent talk about copper on this forum so I wanted to bump this post.


How is copper working for everyone against fireblight?

I sure read a lot about neem oil yesterday and ended up ordering some. Neem oil is the cure all even to fireblight. While it doesn’t do anything to cankers, it does kill a lot of insects and correct a lot of diseases. I was pretty fascinated with what I read.

I have tent caterpillars on a bald cypress that I’ll use neem oil against this year instead of Malathion. This is worth reading. Probably took about 10 minutes:



It’s very hard to say. All my pome fruit got 2 sprays of Southern Ag Liquid Copper plus a sticker, per the fireblight instructions for silver to green tip. I’ve subsequently used Serenade plus a sticker multiple times. I’ve either had fireblight or blossom blast pretty badly on one tree, a pink lady., and minor strikes on other trees. I can’t tell the difference between fireblight and blossom blast at the early stages, and my current strategy is to remove the infected material at the very first sign of infection. It still hasn’t been as bad as last year, but we’ve got an extended period of favorable for fireblight weather ahead.

It’s interesting that the Southern Ag directions call for a fall spray to prevent blossom blast. I hadn’t noticed that until just now, and I wish I knew the reasoning.

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