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Copper Sprays: How they work and avoiding plant injury

Teresa Rusinek, Vegetable Specialist
Eastern New York Commercial Horticulture

June 7, 2018

You may be considering a copper spray to control or prevent certain diseases, particularly bacterial diseases in your crops.  Here's a quick review of 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., 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. 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.  A copper spray acts as a protectant fungicide/bactericide treatment, but lacks post-infection activity.

Because copper products come in different formulations and have different properties, it is important to read all the information on the labels. Besides rates, you will want to know about compatibility with other pesticides, adjuvants, and fertilizers.  Many growers are tank mixing biological fungicides and plant activators with coppers, while many are compatible, some are not, so make sure to check both labels for compatibility or call the manufacture/distributer for technical assistance.

The effectiveness of copper sprays has been correlated with the amount of elemental copper 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 Emeritus 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 phytotoxicity (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. Check the pH of your water source. 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 /solution in spray tank 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. Copper sprays generally cause more phytotoxicity when applied under slow drying conditions, such as when it's wet and cool.   Always read the label and follow copper tank mix partner label instructions.

For a comprehensive list of Copper Products Used for Vegetable Disease Control see:

http://vegetablemdonline.ppath.cornell.edu/NewsArticles/CopperFungicides2012.pdf

and for specific information on copper fungicides in organic disease management see:

http://vegetablemdonline.ppath...

Sources:  Dr. T. A. Zitter, Cornell University and  Dr. David A. Rosenberger, Cornell University

 

This article was published in the June 7th 2018, ENYCHP Vegetable News.  Click here to view the full newsletter.



 



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Upcoming Events

October Last Monday Grant Webinar for Fruit and Vegetable Growers

October 28, 2019
4:00 pm

Are you curious about what grants are available to help your farm business?

To help disseminate information on grants on a consistent basis, ENYCH is offering a "current grants" webinar on the last Monday of every month at 4:00pm

Each month's webinar focuses on 1 grant.  The October webinar topic is TBD but might feature Ag Labor Housing Grants.
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Produce Safety Alliance FSMA Grower Training Course

October 30, 2019
8am - 5pm
Canajoharie, NY

A grower training course developed by the Produce Safety Alliance (PSA) that meets the regulatory requirements of the Food Safety Modernization Act (FSMA) Produce Safety Rule.  At least one person per farm producing more than $25,000 worth of fruits and vegetables must attend this course once.  Participants will receive a certificate of course completion by the Association of Food and Drug Officials. 

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Tarping for Reduced Tillage Workshop

November 2 - November 19, 2019

Are you a vegetable farmer already using tarps? Or are you wondering if and how tarps could work best on your farm?

The Cornell Small Farms Program is excited to announce a series of workshops on tarping for reduced tillage in small-scale vegetable systems, to be held in Maine and New York this fall. The Reduced Tillage (RT) project of the Cornell Small Farms Program supports farmers in adopting scale-appropriate RT practices that can lead to healthy, productive soils and greater profitability. Through the evaluation of novel tools and methods using systems-based field research and on-farm trials, the project helps farmers learn about the approaches that can work for their farm. This work is accomplished in collaboration with the University of Maine, and with support from Northeast SARE.

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Announcements

Resources from CCE ENYCHP!

We are developing new ways to connect with the CCE ENYCHP team this year! We have a Youtube page located at this link. Check out videos on Table Grape Production, Pest Updates and the 20 Minute Ag Manager - in 4 Minutes series

We have a Facebook Page here as well as an Instagram page. We keep these places updated with current projects, events, and other interesting articles and deadlines.

There are also text alerts available. Fruit and vegetable farmers in 17 Eastern NY counties can now receive real time alerts on high risk disease and pest outbreaks texted directly to their cell phone. The Eastern NY Commercial Horticulture program, which is supported by local Cornell Cooperative Extension associations, will now offer text alerts to those that enroll in our program in 2019. 

The text alerts will be reserved for important crop alerts that could impact management decisions immediately. For instance, if there were an outbreak of Late Blight in the area, this would be transmitted to vegetable growers.

Farmers can choose the crop for which they wish to receive updates. Additionally they can request that Ag Business Alerts be sent to them. These alerts might include due dates for crop insurance deadlines, market opportunities etc.

If you have questions, please contact enychp@cornell.edu


Podcasts

Climate Change Adaptations

September 30, 2019
In this episode regional vegetable specialist Elisabeth Hodgdon interviews University of Vermont PHD student Alissa White about a series of interviews with growers in the north east concerning climate change adaptations.

Listeners can access Alissa White’s climate change adaptation survey report and additional information on the project by clicking on the following link:

https://adaptationsurvey.wordpress.com/results/
Alissa’s project was sponsored by a Northeast SARE Graduate Student Grant (GNE17-163).

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