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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

Chautauqua Winter Vegetable Meeting

Event Offers DEC Credits

February 10, 2023
Clymer, NY

Meeting will feature growers from Ohio sharing their production know-how and thoughts on food safety. Other topics include weed control, pesticide safety, and the impact of poor crop nutrition. 0.75 DEC credits in 1a, 23 plus 0.5 in CORE, which is good for all categories. Trade show booths available. 

Meeting cost is $20/person, includes snacks and educational materials. Registration required by 4 pm on Friday, February 3. 

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Orleans Regional Vegetable Meeting

Event Offers DEC Credits

February 15, 2023
Albion, NY

Offering presentations in pesticide safety, tips for managing diseases in vegetable crops, how to attract beneficial insects to your field, herbicide options for cole crops, and strawberry disease information. Meeting cost is $10 per person, payable at the door via cash or check. Pre-registration requested by 5:00 pm on Monday, February 13.

DEC credits available: 2.25 in 1a and 10; 2.0 in 23; 1.5 in 22; and 0.5 in CORE (used in all categories)!!

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NYS Processing Vegetable Industry Roundtable Meeting

Event Offers DEC Credits

March 15, 2023 : Morning Session: Snap Beans, Sweet Corn, and Peas
Batavia, NY

Processing vegetable industry members who grow, manage, or support snap bean, sweet corn, or pea production for Nortera and/or Seneca Foods, should attend this session of the roundtable meeting. You will:

  • Network at this in-person meeting.
  • Learn the results of industry-funded research.
  • Have a voice in Cornell research and extension.
  • Earn 2.0 DEC credits in categories 1a, 10, 23 and CCA recertification credits.

This FREE event is followed by lunch! Pre-registration requested.


March 15, 2023 : Lunch Break and Networking

Lunch is FREE to anyone attending either the Morning Session or the Afternoon Session of the NYS Processing Vegetable Industry Roundtable Meeting. Registration is required.


Event Offers DEC Credits

March 15, 2023 : Afternoon Session: Beets and Carrots
Batavia, NY

Processing vegetable industry members who grow, manage, or support beet or carrot production for Nortera, Seneca Foods and/or Love Beets, should attend this session of the roundtable meeting. You will:

  • Network at this in-person meeting.
  • Learn the results of industry-funded research.
  • Have a voice in Cornell research and extension.
  • Earn 2.0 DEC credits in categories 1a, 10, 23 and CCA recertification credits.

Lunch is provided before this session. It's FREE! Pre-registration requested. 

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Announcements

2022 Year in Review Released

Our 2022 Year in Review report highlights some of our 2022 projects and community outreach efforts impacting commercial vegetable, greenhouse, potato, and dry bean producers in 14 counties of western and central New York, and beyond.
  • Education and Technical Assistance Provided to Providence Farm Collective
  • Engineering Improvements in Biodegradable Mulch
  • Perseverance Leads to Solution for Perennial Sowthistle in Onion
  • Potato Programming Spans Farms of All Sizes
  • Improving Winter High Tunnel Soil Nitrogen Management
  • Laser Scarecrows Tested on Local Farms
  • New York Vegetable Industry Support
Cornell Cooperative Extension is Your Trusted Source for Research-Based Knowledge!

Small-Scale Fresh Mkt Potato Variety Trial Results

This year, the Cornell Vegetable Program planted a potato variety trial focused on commercially available fresh market potato varieties, with the small-scale potato grower in mind. This trial allowed us to test different varieties of potatoes that might be of interest to consumers at farm markets and see how well they perform in a western NY climate. 

We've posted a brief overview of our results on the Potato page.

If you would like the full report (PDF with photos and yield data) emailed to you, email Margie Lund.

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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