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How Copper Sprays Work and Avoiding Phytotoxicity

June 26, 2013

How Copper Sprays Work and Avoiding Phytotoxicity
Copper has been widely used in both conventional and organic production for some time. Copper was one of the first elements used as a plant fungicide (the other was Sulfur). Its discovery can be traced back to the famous origin of Bordeaux mixture, containing a mixture of copper sulfate (CuSO4) and slaked lime, and used for downy mildew control in French vineyards.

Recently, growers have asked me questions regarding the mode of action of copper and had  concerns about phytotoxicity. First, let's begin with how copper controls pathogens. Copper is usually applied in the fixed form which lowers its solubility in water. Fixed coppers include basic copper sulfate (e.g., Cuprofix Ultra Disperss), copper oxide (e.g., Nordox), copper hydroxide (e.g., Kocide, Champ), copper oxychloride sulfate (e.g., COCS), and copper ions linked to fatty acids or other organic molecules (e.g., TennCop, Cueva). The spray solution is actually a suspension of copper particles, and those particles persist on plant surfaces after the spray dries. Copper ions are gradually released from these copper deposits each time the plant surface becomes wet. The gradual release of copper ions from the copper deposits provides residual protection against plant pathogens. At the same time, the slow release of copper ions from these relatively insoluble copper deposits reduces risks of phytotoxicity to plant tissues. Copper ions denature proteins, thereby destroying enzymes that are critical for cell functioning. Copper can kill pathogen cells on plant surfaces, but once a pathogen enters host tissue, it will no longer be susceptible to copper treatments. Thus, copper sprays act as protectant fungicide/bactericide treatments, but lack post-infection activity.

Because different formulations have different properties when used as spray materials, growers need to learn how to read and interpret labels. The effectiveness of copper sprays is highly correlated with the amount of elemental copper that is applied. The metallic copper content varies widely by product. Potency also varies by how the product is prepared. Finely ground copper products are more active than coarsely ground ones. Professor Tom Zitter of Cornell University suggests that for vegetable crops. Begin by choosing a copper product with at least 20% or more copper as the active ingredient to insure the greatest release of copper ions.

There are several suggestions for avoiding phytoxicity (or plant injury) with copper sprays. Limit the copper ion concentration on plant surfaces by using copper products that are relatively insoluble in water, i.e. fixed copper. Copper can accumulate to high levels on plant tissue when sprayed repeatedly to cover new growth and there is no rain. In this situation, after a rain event, a large amount of copper ions may be released leading to phytotoxicity. Solubility of fixed coppers increases under acidic conditions. Copper sprays will become more phytotoxic if they are applied in an acidic solution. Most copper products are formulated to be almost insoluble in water at pH 7.0. As the pH of water decreases the solubility of the copper fungicides increases and more copper ions are released. If the water used is too acidic (below pH 6.0-7.0 depending on the copper formulation) excessive amounts of copper ions could be produced which may cause damage to fruit and foliage. Formulations vary in solubility hydroxides are more soluble than oxychlorides which are more soluble than tribasic copper sulphates and cuprous. Less soluble formulations are usually more persistent. Check the pH of your water source. Copper sprays generally cause more phytotoxicity when applied under slow drying conditions, such as when it's wet and cool.  Always read the label instructions follow the Copper and tank mix partner labels.
For a comprehensive list of Copper Products Used for Vegetable Disease Control see
http://vegetablemdonline.ppath.cornell.edu/NewsArticles/CopperFungicides2012.pdf


Sources: T. A. Zitter, Cornell University Department of Plant Pathology & Plant-Micrbiology and David A. Rosenberger, Professor of Plant Pathology, Cornell University's Hudson Valley Lab


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Upcoming Events

Vegetable Pest and Cultural Management Meeting for Auction Growers (Ontario)

Event Offers DEC Credits

June 27, 2023
Rushville, NY

This on-farm meeting will feature pest management in fresh market vegetables in both field and greenhouse (high tunnel) vegetables, primarily for those growing for wholesale auction. A hands-on demonstration of weed, insect and disease identification in vegetables including management options such as inter-row cover crops, grafting and, where appropriate, spray options will be used to educate growers. Details on each topic will focus on field observations at the farm.

DEC recertification credits will be offered (1.75 credits in categories 10, 1a, 23, 24). 

view details

Vegetable Pest and Cultural Management Meeting for Auction Growers (FLPA)

Event Offers DEC Credits

July 12, 2023
Penn Yan, NY

This meeting will feature pest management in fresh market vegetables in both field and greenhouse (high tunnel) vegetables, primarily for those growing for wholesale auction. A hands-on demonstration of weed, insect and disease identification in vegetables including management options such as inter-row cover crops, grafting and, where appropriate, spray options will be used to educate growers. 

DEC recertification credits will be offered (1.75 credits in categories 10, 1a, 23, 24). 

view details

Vegetable Pest and Cultural Management Meeting for Auction Growers (Seneca)

Event Offers DEC Credits

August 2, 2023
Romulus, NY

This meeting will feature pest management in fresh market vegetables in both field and greenhouse (high tunnel) vegetables, primarily for those growing for wholesale auction. A hands-on demonstration of weed, insect and disease identification in vegetables including management options such as inter-row cover crops, grafting and, where appropriate, spray options will be used to educate growers. 

DEC recertification credits will be offered (1.75 credits in categories 10, 1a, 23, 24). 

view details

Announcements

Ag Water Test Sample Drop-Off Sites in WNY

If you are curious about the quality of your irrigation ponds, streams, wells, or other surface water source, water testing is an important tool to consider. Getting the right test and doing so in a timely manner has been a challenge. Water testing that provides meaningful results requires a quantified generic E. coli test or an Enumeration E. coli test. Some water testing labs only do a potable water test called a presence/absence test. The Enumeration test provides test results as in numbers of (bacterial) colony forming units (CFU or most probable number MPN). Having a number allows you to track the results with a comparable baseline. Each water source should be tested 3-4 times a season and do this each growing season.

Water testing drop-off/pick-up sites have been set up in a number of locations across the region by Lozier Environmental Consulting in Rochester. Water test sample bottles, forms, and information are available at each site. Additional sites are available:
  • A new site has been added in the greater Lockport (Niagara County) area: Flint Brothers Hardware, 2769 Main St, Newfane, NY, 716-778-9654. Samples must be received at this location by Wednesday 9:00am.
  • If you are in Ontario County, contact Nancy Anderson at the CCE Ontario County office in Canandaigua at 585-394-3977 x427. You can pick up the supplies (forms, bottles, instructions, and takes payment) at the CCE office. You will be required to take your sample(s) to a drop-off site in Canandaigua; the bottles will be picked up and delivered to Life Science Labs in Syracuse for analysis.
For assistance in understanding the water test results, contact Robert Hadad or the lab.


New Ag Climate Factsheet Released

The intersection of agricultural production and greenhouse gases is gathering increasing attention. This is an opportune time to consider how vegetable production interacts with carbon sequestration and greenhouse gas emissions, and how using cover crops may alter this picture.

The factsheet, Greenhouse Gases and Soil Organic Carbon in Vegetable Production and the Role of Cover Crops, written by Zach Spangler, Ag Climate Resiliency Specialist with CCE Harvest NY, and Elizabeth Buck, Fresh Market Vegetable Specialist, CCE Cornell Vegetable Program, discusses:
  • Sequestration of atmospheric carbon in agricultural soils as soil organic carbon (SOC). Is vegetable production impacting SOC?
  • Net greenhouse gas emissions of carbon dioxide (CO2), nitrous oxide (N2O), and methane (CH4) from the soil.
  • Impact of cover crops on soil organic carbon, nitrous oxide emissions, and other GHG emissions.


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