Patent Review: Inorganic Copper Oxides in Pesticides and Fertilizers

Authors: Xie Ting, Tan Hui — Patent Examination Cooperation Sichuan Center, Patent Office, China National Intellectual Property Administration


Patent analysis of copper oxides

1 Global filing situation

Copper oxide and cuprous oxide are inorganic pesticides with a long history of application; they were already used for fungicidal purposes as early as the 19th century. However, patent applications concerning the application of copper oxides in pesticides appeared relatively late: in 1913, British patent GB191304571A sought protection for a technical solution in which copper oxide was compounded with phosphates, carbonates, etc., to prepare a disinfectant; in 1925, British patent GB241430A sought protection for the use of copper oxide as an auxiliary in the preparation of a bactericidal and deodorising agent. From the year-by-year volume of patent applications, it can be seen that patents relating to the application of copper oxide and cuprous oxide in the pesticide field appeared in large numbers after 2000, were relatively concentrated in 2005–2017, and reached a maximum annual filing volume of about 160 in 2013. In terms of filing trend, after 2000 the overall number of filings showed a rapid growth trend.

2 Analysis of technical composition

From the global distribution map of application technologies, the largest share of all patent applications is fungicides, followed by insecticides; the number of fungicide and insecticide applications accounted for more than 60% of global applications. Copper, as a trace-element fertiliser essential for plant growth, also played an important role and occupied a place in patent applications, accounting for about 15% of the total.

Analysis of the technical development route of copper oxides

1 Technological evolution in the fertiliser field

Copper is an indispensable trace element for plant growth; although required only in very small amounts, it plays a pivotal role. As early as 1931, GB356195A proposed compounding copper oxide with other compounds to provide fertilisers, insecticides or herbicides. In the years that followed, copper oxide was mostly used as a copper fertiliser in complete nutrient solutions. By 1991, CN1053051A proposed mixing a variety of nutrient elements with rare earths to form a rare-earth fertiliser that could serve both as a culture medium and as a source of multiple nutrient elements. In 1997, CN1165802A proposed a multifunctional compound fertiliser technology, compounding fertiliser components such as copper oxide with other preparations (such as fungicides, herbicides and soil conditioners) as required to obtain different functions. A year later, CN1196345A proposed an organic-inorganic formula fertiliser, formulating the corresponding fertiliser according to soil test results and the types and amounts of nutrient elements required; this was nutrient supply tailored to soil needs and was of epoch-making significance. In 2010, CN101671207A proposed compounding a photosynthesis promoter, a growth regulator, a fungicide and a trace-element fertiliser so as to promote plant photosynthesis, plant growth and yield while controlling plant diseases. By 2015, CN105061084A proposed a controlled-release pesticide fertiliser, applying controlled-release technology to the combination of fertiliser and fungicide/biocide, which can delay the release of the active ingredient and produce a long-lasting effect, and can to a certain extent improve the utilisation rate of the agent and reduce the application rate.

2 Technological evolution in the fungicide field

As early as 1938, GB484115A proposed the combined use of copper oxide and zeolite to prepare a dry-powder fungicide. Then in 1958, GB788668A proposed a technical solution for antibacterial compounding of streptomycin and copper oxide. In 2004, with the development of nanomaterials, US20040067159A1 proposed a technical solution using copper nanoparticles in combination with other biocides to improve the adhesion of the active ingredient on the plant surface and enhance the control effect. In the same year, CN1552456A also proposed using Cu2+ as an antibacterial catalyst. Subsequently, technical solutions for antibacterial compounding of copper oxide and cuprous oxide with various compounds appeared, such as terpene derivatives, mineral salts (US6849276B1), free-radical compounds of copper (KR100752528B1) and microbial spores (US20110033436A1). In 2011, CN101933525A proposed a technical solution for preparing a photocatalytic fungicide by compounding nano cuprous oxide–copper oxide. In 2015, CN104542707A proposed a technical solution in which nano copper oxide is compounded with the pesticide thiram to achieve synergistic, enhanced fungicidal action and photocatalytic degradation.

3 Technological evolution in the insecticide field

Copper oxide is a well-known inorganic copper insecticide in this field; as early as 1949, GB620600A used copper oxide as a sensitiser in insecticidal fumigant compositions. In 1951, FR970319A proposed that combining copper oxide with a substance capable of generating ammonia could effectively control plant pests. In 1990, CN1041354A proposed combining copper salts, insecticides, nutrient elements and plant growth regulators to provide a multi-effect disease control agent. In 2007, KR100752528B1 proposed a technical solution for preparing an insecticide by combining a free-radical compound of copper with copper oxide/copper hydroxide. Subsequently, technical solutions also appeared in which microbial spores were combined with copper salts to slow the development of resistance and improve the control effect.

4 Technological evolution in the plant growth regulator field

In 1991, CN1051112A proposed that copper oxide could serve as a plant growth regulator while also acting as a trace-element fertiliser. In 1996, US5575112A proposed combining a binder with an insoluble inorganic copper compound to regulate the growth of plant roots; the data showed that copper oxide affects indicators such as root length and root fresh weight, and this was the first evidence directly showing that copper oxide can regulate root growth.

Discussion

Because copper fungicides are low in toxicity, safe, broad-spectrum, low in residue, effective against both fungi and bacteria and environmentally safe, they are listed as recommended agents in the production of pollution-free fruit, especially copper preparations such as iron sulfate, copper oxychloride, copper oxide and cuprous oxide. However, copper fungicides are not entirely safe and reliable; abuse and misuse can also cause problems such as phytotoxicity in fruit trees, mite outbreaks and soil pollution. In addition, certain fungi, especially the genus Monilinia (brown rot fungi), are highly copper-tolerant, and their copper-tolerance mechanism is closely related to the production of oxalic acid; oxalic acid acts on copper ions to produce insoluble crystals, inactivating the fungistatic action of copper and thereby reducing its fungistatic toxicity. Therefore, how to improve the control effect of the agent and reduce resistance has become an urgent problem to be solved.

In recent years, with the development of nanomaterials, nano copper oxide has also found certain applications in the pesticide field. Because of their small particle size, nanomaterials are more easily absorbed by plants, which is conducive to improving efficacy. In addition, degradable pesticides are attracting increasing attention, and low-toxicity, high-efficiency, residue-free and environmentally friendly pesticides have increasingly become the goal pursued by people. Nano copper oxide has photocatalytic degradability; using this characteristic to compound inorganic copper oxide with other fungicides/insecticides can effectively reduce drug residues and improve efficacy, and this will become a development trend.