Choosing between copper 8-hydroxyquinoline and an inorganic copper product is not a question of which is stronger – both work – but of which failure mode costs more in a given programme. Inorganic copper is cheap and effective and will mark sensitive fruit. Chelated copper is expensive and gentle and delivers less copper per kilogram. This page sets out the comparison in the terms that matter for a spray programme.
The fundamental difference
|
Inorganic copper |
Copper 8-hydroxyquinoline |
| Common members |
Bordeaux mixture, copper hydroxide, copper oxychloride, copper sulphate |
Copper oxinate, copper quinolinolate – a chelate |
| Copper at application |
Largely free ionic copper |
Chelated, released gradually |
| Solubility |
Some are soluble, some are suspensions |
Essentially insoluble – a deposit on the leaf |
| Copper content |
Varies by product; often 25-50% Cu |
About 18% Cu, in a much heavier molecule |
| Mechanism |
Free copper disrupts microbial enzymes |
Copper delivered into the cell via the ligand, interfering with the same systems |
| Cost per kilogram |
Low |
High |
The three trade-offs that decide it
| Trade-off |
Inorganic copper |
Chelated copper |
How to decide |
| Phytotoxicity |
Real risk – leaf burn, fruit marking, particularly in cool slow-drying conditions and on young tissue |
Substantially lower, because the copper is not freely available at the surface |
If the crop is sensitive or the tissue is young, the saved crop value usually exceeds the price difference |
| Use rate and copper load |
Higher rates; counts fully against annual copper caps |
Lower copper per hectare for comparable protection |
Where a copper cap binds, the chelate lets you stay inside it with fewer sprays or lower rates |
| Cost per hectare |
Lower per kilogram and often lower per application |
Higher per kilogram; the economics only work if it prevents a loss or saves sprays |
Compare cost per hectare per season, not per kilogram of product |
Where inorganic copper is still the right answer
| Situation |
Why inorganic wins |
| Dormant sprays on woody crops |
No green tissue at risk; the cheapest effective option |
| High disease pressure with tolerant varieties |
Raw copper dose is what is needed, and the crop can take it |
| Cost-constrained programmes on commodity crops |
The margin does not support a chelate |
| Bordeaux mixture prepared on farm |
Extremely cheap; the handling drawbacks are accepted as routine |
Where the chelate is worth the money
| Situation |
Why the chelate earns its cost |
| Young tissue and flowering |
Lower risk of marking the very fruit that sets the price |
| Sensitive varieties |
Inorganic copper would need a reduced rate, which reduces protection – the chelate lets you keep both |
| Programmes close to the copper cap |
Fewer grams of copper per hectare for the same protective effect |
| Cool, slow-drying conditions |
Free copper stays in the droplet longer on the leaf and does more damage |
| Mixed spray programmes |
Better compatibility with other actives in many tank mixes |
Copper caps and regulatory pressure
The regulatory trend is the strongest argument for chelated copper, and it is worth stating plainly: several markets cap total elemental copper applied per hectare per year, and those caps have been tightening. That converts the comparison from “which is cheaper per kilogram” to “which delivers the required protection within a fixed copper budget”.
| Constraint |
What it means for product choice |
| Annual copper ceiling |
Every formulation has to be evaluated on copper delivered, not on product mass |
| Organic certification |
Copper is restricted rather than freely allowed; whether a specific chelate is listed depends on the certifier |
| Residue and export requirements |
Some destination markets have their own limits, which can bind before the domestic one |
| Water framework rules |
Runoff and drain contamination rules affect when and where copper can be applied |
The specification differences that matter
| Parameter |
Why it is more critical for a chelate |
| Chloride |
Chelated copper is used on sensitive tissue, where chloride burn is exactly the failure you were trying to avoid – a 0.01% limit is not a formality |
| Sulphate |
Residual from the copper salt; contributes to formulation instability and to phytotoxicity |
| Content |
The dose is calculated on chelated copper, so assay errors translate directly into under- or over-application |
| Loss on drying |
Affects wettable powder dispersion and the assay basis |
| Particle size |
Suspension stability and spray coverage – specify if you mill or blend |
We supply technical material and make no efficacy claims. Crop, rate, interval and permitted claims are defined by the registration in each market, held by the marketing authorisation holder. Confirm the registration position before planning a programme.
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