Developments in copper fungicides

First used on cereal seeds in the 18th century, copper sulphate became a standard routine treatment to prevent bunt on wheat through the 19th century. It was discovered by chance later that century that a mixture of copper sulphate and lime applied to vines, to discourage theft of the grapes, also prevented the loss of leaves from the plants. Further research revealed that the mixture had the unexpected benefit of controlling downy mildew in grapes. The study of such diseases through subsequent years and into the early part of the 20th century provided a clearer understanding of the basic principles of disease control and led to the development of various treatments.

by Francisco Torres, Certis Europe Portfolio Lead – Trees & Vines

By the 1940s proprietary fungicide products were available but dose rates were extremely high, control was variable and some products could be phytotoxic. Drastic reductions in the use rates and new products provided more effective and selective control. The pressure to reduce dose rates is ongoing and has further driven the evolution of low Copper use rated products in recent years.

The European market
Since the early days, copper fungicides, still used in seed dressings as well as plant sprays, have become indispensable in preventing plant diseases worldwide. Europe represents approximately 50% of the US$970 million global market for copper fungicides. Developed countries look for well formulated products, respecting requirements to protect workers from exposure, provide ease of use, etc., whilst emerging markets prefer cheaper, commodity style products. Kocide LLC, established through Mitsui’s acquisition of DuPont’s copper business in 2014, is now one of the world’s largest suppliers of copper products. Production is based in Germany and in the USA and copper fungicide distribution in Europe is through Certis Europe and Spiess Urania.

Advantages
Copper has a very broad spectrum of control of fungal and bacterial pathogens and has been used globally to control more than 200 disease species. The only active ingredient with such a broad disease spectrum, it also has broad crop labelling and is used on more than 120 crops, including vegetables, row crops, citrus, top and soft fruits, vines, turf grass and greenhouse crops. Copper also has the advantage of being safe to plants, animals and the environment and it is accepted in organic production.

With a low risk of developing resistance due to its multi-site activity, copper is an excellent resistance management tool when used with other fungicides with different modes of action (e.g. triazoles, Qols, etc.) and is helping to reduce reliance on synthetic fungicides, some of which are already showing significant resistance problems.

Copper value to soil and plants
Copper is a required mineral for all plant and animal life. However, Cu++ ions are the only biologically active component that can affect target and non-target organisms. They are readily bound to soil organic matter and components (proteins, sulfides, sulfates, etc.) and can only be released by acidic conditions. Copper is therefore used to correct soil deficiencies and as a mineral supplement for animals.

Copper fungicide mode of action
Copper fungicides are protectants that must be applied prior to infection: they have no curative or systemic action. They provide multi-site activity and Cu++ ions interfere with biomolecules (due to their chelating properties) and affect protein structure, the function of enzymes, energy transport systems and membranes. Copper fungicides are different in their physical (crystal) and chemical forms but the active form is always soluble with Cu++ ions actively taken up by fungal spores and bacteria. Once toxic concentrations move inside the cells, the infection process is stopped, offering effective disease control.

Figure 1 How fixed copper compounds (contact fungicides) function: 'BioActiveTM' – essential for biological activity. Source: Kocide LLC

Cu++ ions are the only biologically active (bioactive) component of any copper fungicide responsible for disease control. Copper fungicides do vary in the efficiency of Cu++ ion release, which affects performance.

Figure 2 Comparison of Copper Hydroxide with other copper compounds used as fungicides/bactericides. Source: Kocide LLC

Evolution of copper products
Over the years continuing pressure to reduce rates of copper has led to an evolution of the existing formulations. This has resulted in improved formulations, efficiency and plant safety through new processes and changes to particle surface area and size.

A new process used in the latest Kocide formulations includes a patented co-formulant that surrounds cupric ions in a protective film to create a bioavailable form of copper, which is already broken down and immediately available for disease control. This means that two forms of copper are available: bioavailable copper for immediate usage and fixed crystals for residual activity, thus providing an effective carrier of the Cu++ ions to the target pathogen and sustained release of Cu++ ions in water. The new formulation offers optimum particle shape and size for increased coverage and performance on the plant.

Figure 3 Kocide 2000 contains two sources of active copper. Source: Kocide LLC

These developments in processing and formulation have led to superior disease control in a wide variety of crops including Bacterial diseases in tomatoes, Late Blight in potatoes, Peacock spot in olives, Downy Mildew in vines, broccoli, etc.. In addition there have been improvements in residual effect, rainfastness, suspension and speed of dispersion, compatibility and handling of the products as well as a reduction in dose rates. Such positive developments in response to industry demands for lower rates whilst delivering excellent crop safety with less environmental impact and no effect on beneficial insects and mites will surely help to ensure the future of copper as a valued protectant for a wide variety of crops against a broad spectrum of diseases.

Figure 4 Kocide 2000 combining healthier plants with excellent disease control. Source: Kocide LLC

Francisco Torres, Portfolio Lead for Trees & Vines and responsible for Kocide products within Certis Europe, emphasised their value to growers, “This is an important element of our portfolio, particularly in Southern Europe, providing an excellent tool for growers to protect their specialty crops, to manage diseases resistant to other fungicides and grow their businesses in a sustainable way.”

For more information:
Certis Europe
www.certiseurope.com