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Copper pesticide
View on WikipediaCopper pesticides are copper compounds used as bactericides, algaecides, or fungicides. They can kill bacteria, oomycetes and algae, and prevent fungal spores from germinating. Common forms of fixed copper fungicides include copper sulfate, copper sulfate pentahydrate, copper hydroxide, copper oxychloride sulfate, cuprous oxide, and copper octanoate.[1][2][3][4]
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.[5][6] Both ions have fungicidal and bactericidal activity. Following absorption into the fungus or bacterium, the copper ions will link to various chemical groups (imidazole, phosphate, sulfhydryl, and, hydroxyl 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.[7]
Application
[edit]
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.[8] Excess absorbed copper ions can kill sensitive cells in copper sensitive plants. The leaves of stone fruit trees are more sensitive to copper phytotoxicity than apple leaves. Copper tolerant plant families include Cruciferae, Caryophyllaceae, Gramineae, Leguminosae and Asteraceae.[9]
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.[10] 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.[11]
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.[12] Copper occurs in soils in different forms (ionic, complexed and precipitated) depending on characteristics such as soil texture, organic matter and pH.
Effectiveness
[edit]A strategy to maximize the effectiveness of copper ions is to reduce the particle size of the active substance (micronization) 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 soft rot, Pseudomonas and Xanthomonas leaf spots, and fungal diseases including Botrytis, Plasmopara viticola, Pseudoperonospora humuli, Venturia inaequalis, Bremia lactucae, Peronospora destructor, Taphrina deformans, Stemphylium vesicarium, Cercospora beticola, Phytophthora infestans, Puccinia triticina, Puccinia striiformis and Alternaria solani. Several bacterial pathogens have developed resistance to some copper ion concentrations. These include Pseudomonas syringae, Erwinia amylovora and Xanthomonas campestris pv. vesicatoria.[13]
Copper pesticides may not prevent Sclerotinia blight, some Phytophthora, and Rhizoctonia,[14]
Bordeaux mixture, 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
[edit]In the UK the Soil Association (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.[15] The compounds permitted are copper sulfate, copper hydroxide, cuprous oxide, copper oxychloride, 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.[16] 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
[edit]- ^ [1] Shane, Bill; Copper formulations for fruit crops; Michigan State University Extension; 2011
- ^ David Ritchie, Copper-containing fungicides/bactericides and their use in management of bacterial spot on peaches, Southeast Regional Newsletter. Vol. 4, No. 1, March 2004
- ^ [2] Reregistration Eligibility Decision (RED) for Coppers, USEPA, 2006
- ^ [3] Archived 24 October 2021 at the Wayback Machine Anna LA TORRE, Valeria IOVINO and Federica CARADONIA; Copper in plant protection: current situation and prospects; Phytopathologia Mediterranea (2018), 57, 2, 201−236 www.fupress.com/pm ISSN (print): 0031-9465 Firenze University Press ISSN (online): 1593-2095 DOI: 10.14601/Phytopathol_Mediterr-23407
- ^ [4] S. E. A. McCallan, The Nature of the Fungicidal Action of Copper and Sulfur, Botanical Review Vol. 15, No. 9 (Nov. 1949), pp. 629-643 (15 pages) Published By: Springer
- ^ [5] Pscheidt, Jay W. Copper-based Bactericides and Fungicides, Pacific Northwest Pest Management Handbooks, Oregon State University
- ^ [6] How Copper Sprays Work and Avoiding Phytotoxicity, T. A. Zitter, Cornell University Department of Plant Pathology & Plant-Microbiology and David A. Rosenberger, Professor of Plant Pathology, Cornell University's Hudson Valley Lab, 2013
- ^ [7] Amlal Fouad, Drissi Saad, Makroum Kacem, Maataoui Abdelwahed, Dhassi Khalid, Rahmani Abderrahim & Aït Houssa Abdelhadi (2020) Efficacy of copper foliar spray in preventing copper deficiency of rainfed wheat (Triticum aestivum L.) grown in a calcareous soil, Journal of Plant Nutrition, 43:11, 1617-1626, DOI: 10.1080/01904167.2020.1739294
- ^ Xiong Z.T. and H. Wang, 2005. Copper toxicity and bioaccumulation in Chinese cabbage (Brassica pekinensis Rupr.). Environmental Toxicology 20, 188–194
- ^ [8] GARVER ERNEST, EMMALEA; CAUTION WITH COPPER FUNGICIDES AND SPRAY SURFACTANTS IN VEGETABLES AND FRUITS, University of Delaware Extension, 2013
- ^ [9] Stone, Alex et al; Organic Management of Late Blight of Potato and Tomato with Copper Products; Oregon State University, Published 18 March 2010
- ^ [10] Dave Rosenberger, Options, Benefits, and Liabilities for Copper Sprays in Tree Fruits; Hudson Valley Laboratory, Cornell University; Fruit Notes, Volume 77, Spring, 2012
- ^ [11] Archived 24 October 2021 at the Wayback Machine Anna LA TORRE, Valeria IOVINO and Federica CARADONIA; Copper in plant protection: current situation and prospects; Phytopathologia Mediterranea (2018), 57, 2, 201−236 www.fupress.com/pm ISSN (print): 0031-9465 Firenze University Press ISSN (online): 1593-2095 DOI: 10.14601/Phytopathol_Mediterr-23407
- ^ [12] A. R. Chase, All Coppers Are Not Created Equal, GrowerTalks Pest Management, 2020
- ^ Section 4.11.11, Soil Association Organic Standards for Producer, Version 16.1, April, 2010[permanent dead link]
- ^ Links to forms permitting application of copper fungicide on the website of the Soil Association Archived 15 October 2009 at the Wayback Machine
Copper pesticide
View on GrokipediaHistory
Origins and Invention
The invention of copper-based pesticides traces to the late 19th century, primarily through the development of Bordeaux mixture by French botanist Pierre-Marie-Alexis Millardet. In 1885, amid severe outbreaks of downy mildew (Plasmopara viticola) threatening Bordeaux vineyards—introduced via imported American rootstocks in the 1870s—Millardet observed that grapevines bordering roadsides, treated with a copper sulfate and lime slurry to deter theft by making leaves bitter, remained unaffected by the disease.[10] This empirical observation prompted controlled trials confirming the mixture's fungicidal properties, leading to its formal recommendation for vineyard protection by 1886.[4] Bordeaux mixture, comprising copper(II) sulfate (CuSO₄) at concentrations of 0.9–1.2 kg per 100 liters of water mixed with hydrated lime (Ca(OH)₂) in a 1:1 ratio by weight, represented the first effective chemical control for foliar fungal pathogens on a commercial scale.[11] Its adoption spread rapidly across Europe, credited with averting widespread vine devastation and preserving the French wine industry, which faced potential losses exceeding 80% of production without intervention.[10] Earlier, limited applications of copper existed, such as Prévost's 1807 method of steeping seeds in copper sulfate solution for smut control, but these were narrow in scope and predated systematic pesticidal use.[12] The mechanism underlying its efficacy—copper ions disrupting pathogen enzymes and spore germination—was not fully elucidated until later, but its immediate success stemmed from direct field evidence rather than theoretical models.[13] By the 1890s, variants like Burgundy mixture (copper sulfate with sodium carbonate) emerged, but Bordeaux mixture remained the foundational copper formulation, influencing subsequent inorganic fungicide development amid rising synthetic alternatives.[4]Expansion in Modern Agriculture
The introduction of synthetic fungicides in the mid-20th century, such as dithiocarbamates and benzimidazoles during the 1940s and 1950s, initially curtailed copper pesticide applications in conventional agriculture by offering greater efficacy at lower doses—reducing typical copper rates from 20-30 kg/ha/year or higher in Europe to more targeted uses.[5][14] However, escalating issues with synthetic fungicide resistance, environmental persistence, and regulatory bans—exemplified by EU restrictions on substances like maneb and chlorothalonil—reinvigorated copper's role as a reliable, broad-spectrum alternative with minimal resistance development due to its multisite mode of action.[15][16] This resurgence accelerated with the expansion of organic farming from the 1990s onward, where copper compounds like Bordeaux mixture and copper hydroxide are among the few permitted fungicides for controlling pathogens such as Plasmopara viticola in grapes and Phytophthora in potatoes.[17] Global organic agricultural land grew from 11 million hectares in 1999 to over 96 million hectares by 2023, amplifying copper demand as organic production emphasized non-synthetic inputs amid rising consumer preference for residue-free crops.[18] In the EU, organic regulations cap copper at 6 kg/ha/year (with a 28 kg/ha five-year average allowance), yet actual usage in 12 countries reached 3,258 metric tons of copper metal annually as of 2017, concentrated in perennial crops like grapevines (accounting for ~50% of applications), olives, and almonds.[19][20] Market data underscores this trend: the global copper fungicides sector, valued at $385 million in 2023, is forecasted to expand to $587 million by 2032 at a 4.79% CAGR, driven by organic sector growth and integrated pest management in conventional systems for high-value crops like citrus, tomatoes, and walnuts.[21] In regions like the Mediterranean and California, copper applications persist at 2-4 kg/ha/year in organic vineyards, sustaining yields against foliar diseases where synthetic alternatives face phase-outs.[19] This expansion, while enabling pathogen control without reliance on single-site synthetics, has elevated soil copper levels to over 500 mg/kg in intensively treated orchards and vineyards, prompting ongoing research into minimization strategies like precision spraying and bioalternatives.[14][15]Chemical Composition and Mechanism
Common Compounds and Formulations
Copper-based pesticides primarily utilize fixed copper compounds to minimize phytotoxicity while providing effective fungicidal and bactericidal action. The most prevalent active ingredients include copper hydroxide (Cu(OH)₂), which constitutes the majority of fixed copper fungicides due to its low solubility and reduced risk of copper ion release compared to soluble forms.[2] Copper oxychloride (approximately Cu₂Cl(OH)₃) is another widely used compound, often formulated as a 50% wettable powder (WP) containing 50% metallic copper equivalent, valued for its stability in storage and adhesion to plant surfaces.[22] Tribasic copper sulfate (a complex of cupric sulfate, tricupric hydroxide, and hemihydrate) and cuprous oxide (Cu₂O) serve as alternatives in specific applications, offering varying rates of copper release tailored to disease pressure.[23] The foundational formulation, Bordeaux mixture, emerged in the late 19th century and consists of copper sulfate pentahydrate (CuSO₄·5H₂O) combined with hydrated lime (calcium hydroxide, Ca(OH)₂) in water, typically in a 1:1:100 ratio by weight (e.g., 1 kg copper sulfate, 1 kg lime per 100 liters water for a 1% concentration).[24] This mixture forms an insoluble basic copper sulfate precipitate that adheres to foliage, releasing copper ions slowly upon contact with moisture and pathogens; higher concentrations, such as 10-10-100, are used for pastes or severe infections but increase phytotoxicity risks.[1] Modern fixed copper products often incorporate these compounds into emulsifiable concentrates, wettable powders, or flowable suspensions, with inert ingredients like surfactants enhancing dispersion and coverage; for instance, copper hydroxide formulations may include fatty acids to form soap-like suspensions for better leaf wetting.[7]| Compound | Chemical Formula | Typical Formulation Type | Key Characteristics |
|---|---|---|---|
| Copper Hydroxide | Cu(OH)₂ | Wettable powder or flowable | Low solubility, common in organic-approved products; metallic copper content ~50-60%[2] |
| Copper Oxychloride | Cu₂Cl(OH)₃ | 50% WP | Stable, good adhesion; used globally for broad-spectrum control[22] |
| Bordeaux Mixture | CuSO₄ + Ca(OH)₂ | Tank-mix suspension | Insoluble precipitate; classic but requires on-site preparation to avoid instability[24] |
| Tribasic Copper Sulfate | Complex (CuSO₄·3Cu(OH)₂·½H₂O) | Granular or dispersible | Intermediate release rate; less phytotoxic than pure sulfate[23] |
Mode of Action Against Pathogens
Copper pesticides operate as contact protectants, releasing copper ions (primarily Cu²⁺) from formulations such as copper hydroxide or copper oxychloride upon application to plant surfaces, where they exert toxicity against fungal and bacterial pathogens through direct interaction with spores or cells prior to plant infection.[2][25] These ions are sparingly soluble in fixed copper compounds, providing a slow-release mechanism that maintains effective concentrations on leaf surfaces, enhanced by environmental factors like dew or low pH, which increase solubility without systemic uptake into the plant.[2] Classified by the Fungicide Resistance Action Committee (FRAC) as Group M1, copper-based fungicides exhibit multi-site activity, targeting multiple essential cellular components in pathogens rather than a single enzyme or pathway, which confers a low risk of resistance development compared to single-site inhibitors.[26] The core mechanism involves non-specific denaturation and disruption of proteins and enzymes; copper ions bind to sulfhydryl (-SH) groups and solvent-accessible sulfur atoms in iron-sulfur (Fe-S) cluster proteins, such as those involved in amino acid biosynthesis (e.g., isopropylmalate dehydratase) and DNA replication/repair, thereby inhibiting critical metabolic and replicative processes.[27][28] Further toxicity arises from copper's redox cycling between Cu⁺ and Cu²⁺ states, generating reactive oxygen species (ROS) that induce oxidative damage to pathogen membranes, lipids, and additional proteins, compromising membrane integrity and leading to cell leakage and death.[27] Against fungal spores, this prevents germination by interfering with early cellular development, while in bacteria like Xanthomonas or Pseudomonas, it similarly disrupts enzymatic functions and energy production without curative effects post-infection.[2][28] Copper's broad-spectrum action extends to oomycetes but lacks activity against established infections, necessitating preventive timing in disease management programs.[25]Agricultural Applications
Targeted Crops and Pathogens
Copper-based pesticides function as broad-spectrum protectants against fungal, oomycete, and bacterial pathogens in diverse agricultural crops, with particular reliance in organic systems where synthetic alternatives are restricted.[25][2] They are applied preventively, as their contact action requires coverage before pathogen establishment.[25] In perennial crops like grapes, copper formulations such as Bordeaux mixture target downy mildew caused by Plasmopara viticola and provide partial control of powdery mildew.[25] For tree fruits including apples, pears, peaches, plums, and nectarines, they manage fire blight (Erwinia amylovora), bacterial canker (Pseudomonas syringae), peach leaf curl (Taphrina deformans), shot hole disease (Wilsonomyces carpophilus), scab (Venturia inaequalis in apples), and moniliosis (Monilinia spp.), often via dormant-season sprays such as a 3% copper sulfate solution (300 g per 10 L water) applied in early spring (February-March) before bud swell at average daily temperatures of +5–6°C to target overwintering pathogens. For young trees, a 1% solution is often preferred to avoid phytotoxicity; thorough application covers branches, trunk, and soil under the tree, and should be avoided after bud break to prevent burns.[29][25][30] In nuts such as walnuts and olives, copper controls walnut blight (Xanthomonas campestris pv. juglandis) and olive leaf spot.[29][25] Among vegetables and field crops, solanaceous plants like tomatoes and potatoes receive applications against bacterial spot and speck (Xanthomonas spp.), early blight (Alternaria solani), and late blight (Phytophthora infestans).[31][2] Brassicas such as cabbage and collards benefit from control of black rot (Xanthomonas campestris pv. campestris), while peppers and parsley are protected from bacterial spot.[2] Leafy greens like spinach and lettuce, as well as cucurbits like squash, use copper for downy mildew (Peronospora spp.) and Alternaria leaf spot.[25][2] Citrus crops employ dormant Bordeaux mixture applications to suppress bacterial blast, Phytophthora brown rot, and Septoria spot.[29]
| Crop Category | Key Targeted Pathogens/Diseases |
|---|---|
| Grapes | Downy mildew (Plasmopara viticola), powdery mildew[25] |
| Stone Fruits (Peach, Nectarine, Apricot) | Peach leaf curl (Taphrina deformans), shot hole (Wilsonomyces carpophilus), bacterial canker (Pseudomonas syringae)[29][25] |
| Pome Fruits (Apple, Pear) | Fire blight (Erwinia amylovora)[29][25] |
| Tomatoes/Potatoes | Bacterial spot/speck (Xanthomonas spp.), early blight (Alternaria solani), late blight (Phytophthora infestans)[31][2] |
| Brassicas (Cabbage, Collards) | Black rot (Xanthomonas campestris pv. campestris), Alternaria leaf spot[2] |
| Citrus | Bacterial blast, Phytophthora brown rot, Septoria spot[29] |
| Walnuts/Olives | Walnut blight (Xanthomonas campestris pv. juglandis), olive leaf spot[29][25] |
Methods of Application and Dosage
Copper pesticides are predominantly applied via foliar spraying to achieve direct contact with plant surfaces targeted by fungal and bacterial pathogens.[2] This method involves using pressurized sprayers, boom sprayers for field crops, or air-blast equipment for orchards and vineyards to ensure uniform coverage of leaves, stems, and fruits.[32] Formulations such as liquid concentrates, wettable powders, or dispersible granules are diluted in water, often with adjuvants like horticultural oils or surfactants to improve adhesion and penetration, though compatibility must be verified to avoid phytotoxicity.[33] Fixed copper compounds, exemplified by Bordeaux mixture, require on-site preparation by combining copper sulfate with hydrated lime to reduce phytotoxic free copper ions.[25] Application timing emphasizes prevention, with sprays initiated just before periods of high disease risk, such as prolonged wet weather or early-season pathogen activity, rather than as a curative measure post-infection.[34] Reapplications occur at intervals of 7-14 days, adjusted for rainfall and disease pressure, using higher rates during conducive conditions.[35] Dust formulations exist but are less common due to drift risks and uneven coverage compared to sprays.[2] Dosages are specified on product labels in terms of metallic copper equivalent (MCE), standardizing efficacy across formulations, and vary by crop, disease severity, and regulatory limits.[2] For instance, liquid copper concentrates like Bonide Liquid Copper are applied at 12 ounces per gallon of water to thoroughly wet plants, repeated every 7-10 days.[36] Copper oxychloride formulations recommend 2-3 grams per liter of water for most crops.[37] In organic systems, the European Union caps annual copper application at 6 kilograms per hectare for perennial crops, with certification bodies enforcing recognition of these rates to minimize accumulation.[38] United States guidelines defer to label instructions without a federal annual limit, though state laws and best practices advise consulting extension services for crop-specific rates, such as 0.5-2 pounds MCE per acre per application for vegetables.[39] Higher rates are used under high disease incidence, but always balanced against phytotoxicity risks at elevated concentrations above 1-2% copper.[35]| Crop Example | Formulation | Typical Rate (MCE basis) | Source |
|---|---|---|---|
| Vegetables (e.g., tomatoes) | Copper hydroxide | 0.25-1 lb/acre per application | [40] |
| Fruits (e.g., citrus) | Copper-based with oil | <0.5% copper equivalent | [41] |
| Grapes | Bordeaux mixture | Up to 6 kg Cu/ha annually (EU organic) | [38] |
Efficacy Data
Field Trials and Empirical Evidence
Field trials have consistently demonstrated the efficacy of copper-based fungicides, such as Bordeaux mixture and copper hydroxide, in controlling fungal pathogens in various crops, particularly through contact action that disrupts pathogen spore germination and mycelial growth. In replicated plot experiments on potatoes, applications of copper fungicides, including Bordeaux mixture, provided foliage protection against Phytophthora infestans (late blight) comparable to standard treatments, resulting in significant yield increases over untreated controls; for instance, eight trials showed reduced blight severity and higher tuber yields with copper oxychloride and other formulations applied at intervals of 7-14 days.[42][43] For grapevines, field studies on downy mildew (Plasmopara viticola) have shown copper hydroxide formulations achieving high control rates, with disease incidence limited to under 5% in treated plots versus over 50% in untreated ones when applied preventively every 7-10 days during high-risk periods; combining copper with adjuvants like chitosan further enhanced efficacy, reducing sporulation by 80-90% in multi-year trials across European vineyards.[44][45] Reduced-dose strategies, using 1-2 kg/ha elemental copper, maintained efficacy above 85% while minimizing accumulation, as validated in organic viticulture trials.[45] In citrus, copper hydroxide trials against bacterial canker (Xanthomonas citri) reported lesion reductions of 70-90% on grapefruit foliage with weekly sprays, outperforming untreated benchmarks without inducing resistance due to its multi-site mode of action.[46] Similarly, for coffee leaf rust (Hemileia vastatrix), field applications of copper combined with systemic fungicides extended protection durations up to 6 weeks, lowering disease severity by 60-80% in commercial plots in regions like Colombia.[47] These results underscore copper's reliability in empirical settings, though efficacy is weather-dependent, with rainfastness improved by formulation type.[48]Comparative Performance Against Synthetics
Copper-based pesticides, functioning primarily as contact protectants, demonstrate reliable preventive efficacy against fungal and bacterial pathogens but typically underperform modern synthetic fungicides in overall disease suppression, particularly where curative or systemic action is required. Synthetic alternatives, including multi-site contacts like mancozeb and single-site systemics such as metalaxyl or dimethomorph, often achieve 10-20% higher levels of disease control in high-pressure scenarios due to their ability to penetrate plant tissues and halt established infections. For example, in field trials on potato late blight (Phytophthora infestans), combinations of metalaxyl + mancozeb reduced disease severity more effectively than copper hydroxide or mancozeb alone, with the systemic formulation yielding superior tuber protection and minimizing defoliation.[49] [50] In grapevine downy mildew (Plasmopara viticola), copper formulations like Bordeaux mixture provide 70-90% preventive control when applied frequently, yet synthetic systemics such as ametoctradin or cymoxanil deliver comparable or superior suppression (up to 95%) with fewer applications and better persistence under wet conditions. Empirical data from European vineyards highlight that copper's rain-washoff necessitates 10-15 sprays per season for adequate coverage, whereas synthetics maintain efficacy with 6-8 applications, reducing labor and improving cost-effectiveness.[51] [52] However, copper's multi-site mode of action confers a lower risk of pathogen resistance development compared to single-site synthetics, enabling sustained performance in integrated programs over multiple seasons without efficacy loss.[53]| Crop/Pathogen | Copper Efficacy (% Control) | Synthetic Efficacy (% Control) | Key Reference |
|---|---|---|---|
| Potato Late Blight | 60-75% (preventive) | 80-90% (systemic/contact combo) | [web:45 URL] |
| Grapevine Downy Mildew | 72-89% (high dose) | 85-95% (systemic) | [web:38 URL] |
