Copper pesticides are copper compounds used as

bactericide A bactericide or bacteriocide, sometimes abbreviated Bcidal, is a substance which kills bacteria. Bactericides are disinfectants, antiseptics, or antibiotics. However, material surfaces can also have bactericidal properties based solely on thei ...

algaecide Algaecide or algicide is a biocide used for killing and preventing the growth of algae, often defined in a loose sense that, beyond the biological definition, also includes cyanobacteria ("blue-green algae"). An algaecide may be used for controlle ...

s, or fungicides. They can kill bacteria,

oomycete Oomycota forms a distinct phylogenetic lineage of fungus-like eukaryotic microorganisms, called oomycetes (). They are filamentous and heterotrophic, and can reproduce both sexually and asexually. Sexual reproduction of an oospore is the resul ...

s and algae, and prevent fungal spores from germinating. Common forms of fixed copper fungicides include

copper sulfate Copper sulfate may refer to: * Copper(II) sulfate, CuSO4, a common compound used as a fungicide and herbicide * Copper(I) sulfate Copper(I) sulfate, also known as cuprous sulfate, is an inorganic compound with the chemical formula Cu2 SO4. It ...

, copper sulfate pentahydrate, copper hydroxide, copper oxychloride sulfate,

cuprous oxide Copper(I) oxide or cuprous oxide is the inorganic compound with the formula Cu2O. It is one of the principal oxides of copper, the other being or copper(II) oxide or cupric oxide (CuO). This red-coloured solid is a component of some antifouling p ...

, and copper octanoate. Copper fungicides work by slowly releasing positively charged copper ions Cu⁺ and Cu²⁺ in concentrations that interact with nucleic acids, interfere with energy transport, disrupt enzyme activity, and affect the integrity of cell membranes of pathogens. Both ions have fungicidal and bactericidal activity. Following absorption into the fungus or bacterium, the copper ions will link to various chemical groups (

imidazole Imidazole (ImH) is an organic compound with the formula C3N2H4. It is a white or colourless solid that is soluble in water, producing a mildly alkaline solution. In chemistry, it is an aromatic heterocycle, classified as a diazole, and has non-a ...

phosphate In chemistry, a phosphate is an anion, salt, functional group or ester derived from a phosphoric acid. It most commonly means orthophosphate, a derivative of orthophosphoric acid . The phosphate or orthophosphate ion is derived from phosph ...

, sulfhydryl, and,

hydroxyl In chemistry, a hydroxy or hydroxyl group is a functional group with the chemical formula and composed of one oxygen atom covalently bonded to one hydrogen atom. In organic chemistry, alcohols and carboxylic acids contain one or more hydro ...

groups) present in many proteins and disrupt their functions. Copper ions can kill pathogen cells on plant surfaces, but once a pathogen enters host plant tissue, it is no longer susceptible to copper treatments at the prescribed concentrations. The prescribed copper ion concentrations lack post-infection activity. Higher copper ion concentrations harm the host plant.

Application

Copper pesticide is applied as a contact protective foliar spray, so it remains deposited on leaf surfaces. A small concentration of copper ions may be taken up by plants as essential nutrients. Copper foliar sprays are also applied to correct plant copper deficiency. Excess absorbed copper ions can kill sensitive cells in copper sensitive plants. The leaves of

stone fruit In botany, a drupe (or stone fruit) is an indehiscent fruit in which an outer fleshy part ( exocarp, or skin, and mesocarp, or flesh) surrounds a single shell (the ''pit'', ''stone'', or ''pyrena'') of hardened endocarp with a seed (''kernel' ...

trees are more sensitive to copper

phytotoxicity Phytotoxicity describes any adverse effects on plant growth, physiology, or metabolism caused by a chemical substance, such as high levels of fertilizers, herbicides, heavy metals, or nanoparticles. General phytotoxic effects include altered plan ...

than apple leaves. Copper tolerant plant families include

Cruciferae Brassicaceae () or (the older) Cruciferae () is a medium-sized and economically important family of flowering plants commonly known as the mustards, the crucifers, or the cabbage family. Most are herbaceous plants, while some are shrubs. The leav ...

Caryophyllaceae Caryophyllaceae, commonly called the pink family or carnation family, is a family of flowering plants. It is included in the dicotyledon order Caryophyllales in the APG III system, alongside 33 other families, including Amaranthaceae, Cactacea ...

Gramineae Poaceae () or Gramineae () is a large and nearly ubiquitous family of monocotyledonous flowering plants commonly known as grasses. It includes the cereal grasses, bamboos and the grasses of natural grassland and species cultivated in lawns and ...

, Leguminosae and

Asteraceae The family Asteraceae, alternatively Compositae, consists of over 32,000 known species of flowering plants in over 1,900 genera within the order Asterales. Commonly referred to as the aster, daisy, composite, or sunflower family, Compositae w ...

. Copper phytotoxicity worsens under slow drying conditions. Adding surfactants with copper fungicides may increase injury to plant foliage. Copper ions release more readily under acidic conditions and copper pesticides, except copper sulfate pentahydrate, should not be used with acid forming products. Copper fungicides can be highly effective if applied prophylactically and with complete coverage of all plant foliar surfaces, including the undersides of leaves where the pathogen typically sporulates. Copper pesticides must be used in quantities that minimizes long term copper accumulation in the soil. Accumulated copper in soils can inhibit root growth and adversely affect microorganisms and earthworms. Finely ground copper formulations are more active than coarsely ground formulations. Coarsely ground formulations should be avoided to limit long term bioaccumulation and toxicity. Copper occurs in soils in different forms (ionic, complexed and precipitated) depending on characteristics such as

soil texture Soil texture is a classification instrument used both in the field and laboratory to determine soil classes based on their physical texture. Soil texture can be determined using qualitative methods such as texture by feel, and quantitative methods ...

, organic matter and pH.

Effectiveness

A strategy to maximize the effectiveness of copper ions is to reduce the particle size of the active substance (

micronization Micronization is the process of reducing the average diameter of a solid material's particles. Traditional techniques for micronization focus on mechanical means, such as milling and grinding. Modern techniques make use of the properties of supe ...

) and copper microencapsulation. These improve relative coverage of treated plant surfaces or extend copper ion releases. Modern copper application dose rates may be as low as 200-400g per treatment per hectare. Copper pesticides can be effective in preventing bacterial diseases, including

Erwinia ''Erwinia'' is a genus of Enterobacterales bacteria containing mostly plant pathogenic species which was named for the famous plant pathologist, Erwin Frink Smith. It contains Gram-negative bacteria related to ''Escherichia coli'', ''Shigella'', ...

soft rot,

Pseudomonas ''Pseudomonas'' is a genus of Gram-negative, Gammaproteobacteria, belonging to the family Pseudomonadaceae and containing 191 described species. The members of the genus demonstrate a great deal of metabolic diversity and consequently are able t ...

and

Xanthomonas ''Xanthomonas'' (from greek: ''xanthos'' – “yellow”; ''monas'' – “entity”) is a genus of bacteria, many of which cause plant diseases. There are at least 27 plant associated ''Xanthomonas spp.'', that all together infect at least 400 ...

leaf spots, and fungal diseases including Botrytis,

Plasmopara viticola ''Plasmopara viticola'', the causal agent of grapevine downy mildew, is a heterothallic oomycete that overwinters as oospores in leaf litter and soil. In the spring, oospores germinate to produce macrosporangia, which under wet condition releas ...

Pseudoperonospora humuli ''Pseudoperonospora humuli'' is a plant pathogen that causes downy mildew on hops. Hosts and symptoms Downy mildew on hops is caused by the pathogen ''Pseudoperonospora humuli'', an oomycete protist. ''P. humuli'' is an obligate biotrophic pa ...

Venturia inaequalis ''Venturia inaequalis'' is an ascomycete fungus that causes the apple scab disease. Systematics ''Venturia inaequalis'' anamorphs have been described under the names ''Fusicladium dendriticum'' and ''Spilocaea pomi''. Whether ''V. inaequalis'' i ...

, Bremia lactucae, Peronospora destructor, Taphrina deformans, Stemphylium vesicarium, Cercospora beticola,

Phytophthora infestans ''Phytophthora infestans'' is an oomycete or water mold, a fungus-like microorganism that causes the serious potato and tomato disease known as late blight or potato blight. Early blight, caused by '' Alternaria solani'', is also often called "p ...

Puccinia triticina Wheat leaf rust (''Puccinia triticina'') is a fungal disease that affects wheat, barley, rye stems, leaves and grains. In temperate zones it is destructive on winter wheat because the pathogen overwinters. Infections can lead up to 20% yield ...

, Puccinia striiformis and

Alternaria solani ''Alternaria solani'' is a fungal pathogen that produces a disease in tomato and potato plants called early blight. The pathogen produces distinctive "bullseye" patterned leaf spots and can also cause stem lesions and fruit rot on tomato and tu ...

. Several bacterial pathogens have developed resistance to some copper ion concentrations. These include

Pseudomonas syringae ''Pseudomonas syringae'' is a rod-shaped, Gram-negative bacterium with polar flagella. As a plant pathogen, it can infect a wide range of species, and exists as over 50 different pathovars, all of which are available to researchers from intern ...

Erwinia amylovora Fire blight, also written fireblight, is a contagious disease affecting apples, pears, and some other members of the family Rosaceae. It is a serious concern to apple and pear producers. Under optimal conditions, it can destroy an entire orchard ...

and

Xanthomonas campestris ''Xanthomonas campestris'' is a bacterium that causes a variety of plant diseases, including "black rot" in cruciferous vegetables and bacterial wilt of turfgrass. It is also used in the commercial production of xanthan gum, a high-molecular-we ...

pv. vesicatoria. Copper pesticides may not prevent

Sclerotinia ''Sclerotinia'' is a genus of fungi A fungus ( : fungi or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as the more familiar mushrooms. These organisms are ...

blight, some

Phytophthora ''Phytophthora'' (from Greek (''phytón''), "plant" and (), "destruction"; "the plant-destroyer") is a genus of plant-damaging oomycetes (water molds), whose member species are capable of causing enormous economic losses on crops worldwide, a ...

, and

Rhizoctonia ''Rhizoctonia'' is a genus of fungi in the order Cantharellales. Species form thin, effused, corticioid basidiocarps (fruit bodies), but are most frequently found in their sterile, anamorphic state. ''Rhizoctonia'' species are saprotrophic, bu ...

Bordeaux mixture Bordeaux mixture (also called ''Bordo Mix'') is a mixture of copper(II) sulphate (CuSO4) and quicklime ( Ca O) used as a fungicide. It is used in vineyards, fruit-farms and gardens to prevent infestations of downy mildew, powdery mildew and other ...

, made by adding copper sulfate and calcium hydroxide to water, was one of the first fungicides used by Pierre-Marie-Alexis Millardet, a French viticulturist during the mid-1800s.

Use in organic farming

In the UK the

Soil Association The Soil Association is a British registered charity. The organisation activities include campaigning – against intensive farming, for local purchasing and public education on nutrition – and certification of organic foods. It was establ ...

(one of the organic certification authorities) permits farmers to use some copper fungicides on organic land used for the production of certified organic crops only if there is a major threat to crops. The compounds permitted are

, copper hydroxide,

copper oxychloride Dicopper chloride trihydroxide is the chemical compound with the formula Cu2(OH)3Cl. It is often referred to as tribasic copper chloride (TBCC), copper trihydroxyl chloride or copper hydroxychloride. It is a greenish crystalline solid encount ...

, copper ammonium carbonate (at a maximum concentration of 25 g/L), and copper octanoate. According to the Soil Association the total copper that can be applied to organic land is 6 kg/ha/year.Links to forms permitting application of copper fungicide on the website of the Soil Association
This limit is designed so that the amount of copper in the soil does not exceed the limits specified in the Soil Association standards for heavy metals.

Notes

{{reflist Pesticides Algaecides Fungicides Bactericides Copper(II) compounds