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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

2018 Empire State Producers EXPO

Event Offers DEC Credits

January 16 - January 18, 2018
1.25 hr sessions throughout each day
Syracuse, NY

The 2018 Empire State Producers Expo combines the major fruit, flower and vegetable associations of New York State in order to provide a comprehensive trade show and educational conference for New York producers, as well as the surrounding states and Eastern Canada. 
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Growing, Washing and Packing High Tunnel Winter Greens: Doing It and Doing It Well

January 18, 2018
9:00 AM - 4:00 PM
Saratoga Springs, NY

NOFA-NY 2018 Winter Conference: Pre-Conference Event
This event promises to help growers bring their winter greens production to the next level -- both in the high tunnel and in the packshed. There will be an emphasis on best management practices in the high tunnel, especially practices which support long term soil health and fertility. In the packshed, processing efficiency and food safety will both be stressed.

The day will begin at 9:00 am in conference room Broadway 1, with workshops on issues and opportunities in winter high tunnel production and best practices for postharvest handling, including food safety concerns.

Upon completion of the workshops at 10:30 am, everyone will board a bus and travel to Paul and Sandy Arnold's Pleasant Valley Farm in Argyle, NY for a farm tour and farmer-led discussions in the high tunnel and packshed. A farm to table lunch, with a vegetarian option, will be served at the farm. After lunch, the tours and discussions will continue and then everyone will come together for a Q&A session with hot cider and light snacks. The bus will leave the farm at about 3:15 pm and should be back at the hotel by 4:00 pm. 
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Produce Grower Food Safety Training - FSMA and GAPs/HGAPs

January 30, 2018 : FSMA and GAPs/HGAPs Produce Safety Alliance Training Course

January 31, 2018 : Workshop on Farm Food Safety Plan Writing

This program is for fruit and vegetable growers who need Food Safety Modernization Act (FSMA) certification or GAPs/HGAPs (Good Agricultural Practices/ Harmonized Good Agricultural Practices) training required by buyers (i.e. 3rd-party food safety audits based on a written food safety plan) or if you are just interested in learning about produce safety.

Over the course of the training, certified Produce Safety Alliance trainers will cover content contained in these seven modules:
  • Introduction to Produce Safety
  • Worker Health, Hygiene, and Training
  • Soil Amendments
  • Wildlife, Domesticated Animals, and Land Use 
  • Agricultural Water (Part I: Production Water; Part II: Postharvest Water) 
  • Postharvest Handling and Sanitation 
  • How to Develop a Farm Food Safety Plan
An optional farm food safety plan writing workshop is offered on January 31. Separate registration required.
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Announcements

Cornell Commercial Vegetable Guidelines Available

The 2018 Cornell Integrated Crop and Pest Management Guidelines for Commercial Vegetable Production are now available!

Written by Cornell University specialists, this publication is designed to offer producers, seed and chemical dealers, and crop consultants practical information on growing and managing vegetable crops in New York State. Topics include general culture, nutrient management, transplant production, postharvest handling, organic production, and managing common vegetable crop pest concerns. A preview of the Vegetable Guidelines can be seen online.

Highlighted changes in the 2018 Vegetable Guidelines include:
  • Updated pesticide options for economically important vegetable crop pests.
  • Significantly revised pest management practices.
  • New onion and sweet corn IPM scouting report forms.
Cornell Crop and Pest Management Guidelines are available as a print copy ($41), online-only access ($41), or a package combining print and online access ($57.50). Shipping charges will be added to your order. Cornell Guidelines can be obtained through your local Cornell Cooperative Extension office, or from the Cornell Store at Cornell University or call (844) 688-7620.

Available: 2017 Certified Seed Potato Directory

The 2017 NYS Certified Seed Potato Crop Directory is now available. There is a wealth of information on NYS potato seed certification, as well as on the varieties grown for certification in 2017. The varieties include standards for processing and tablestock, newer varieties and numbered lines, and specialty/heirloom varieties. Brief summaries of the varieties' maturity, appearance, yield potential, and major disease susceptibility are included. Contact info for the growers with seed supplies of each variety is included. There is also a listing of the inspectors from the NYS Department of Agriculture and Markets in Albany and Syracuse.

Growing for Wholesale Guidelines Available

Grading and packing guidelines are now available for 16 commonly grown specialty crops in NYS: broccoli crowns, Brussels sprouts, corn, green peppers, cucumbers, green cabbage, red cabbage, savory cabbage, cauliflower, eggplant, green beans, jalapenos, poblanos, Hungarian hot peppers, summer squash, and zucchini.

Acceptable quality standards and common defects that should be sorted out on the grading line are depicted in these resources, both visually and in outline form. Find all of the grading sheets here.

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