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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

Ag Manager Webinar Series: Ag Tax Topics - Sales Tax and Property Tax Issues for Ag in NYS

August 27, 2019
12:30 - 12:50pm

Join Liz Higgins from the CCE ENYCHP every other Tuesday at 12:30pm throughout the summer as she discusses pertinent business topics for busy farm managers.
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Willsboro Farm High Tunnel Twilight Meeting

August 27, 2019
5:00pm - 7:00pm
Willsboro, NY

Join vegetable specialists Elisabeth Hodgdon, Jud Reid, and farm manager Mike Davis for a high tunnel and field tour at Cornell's Willsboro Research Farm, where they will share research results for the following projects: 
  • Striped cucumber beetle management suing netting and row cover
  • Varietal differences in cucumber susceptibility to striped cucumber beetle
  • Ground cherry and goldenberry production in field and high tunnel environments
  • Overwintered high tunnel spinach nitrogen fertility 

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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

Biweekly Vegetable News Podcast - Episode 9 - 08/21/19

August 21, 2019
The August 21st, 2019 edition of the Eastern New York Vegetable News covers the following topics:

Changes to Worker Housing Regulations in the Farmworker Fair Labor Practices Act (1:25)
Managing Alternaria Leaf Spot and Head Rot on Broccoli (4:25)
Gauging Winter Squash Maturity for Harvest (10:05)
Insects in Hemp, especially European Corn Borers (18:33)
Guidance on the Dropped Covered Produce Provision of the Food Safety Modernization Act (22:53)
Cucurbit Downy Mildew Management Update (27:02)
Report from the BioControl Field Day and Weed Management Recommendations (31:07)
Day Neutral Strawberries (40:33)

Here are links to additional resources mentioned in the episode:

Current Housing Regulations for Seasonal and Migrant Farmworkers
(On January 1, 2020, these will now apply to farms housing any number of seasonal and migrant farmworkers)

Public Health Law, section 225, NYCRR Title 10 Health, Part 15, Migrant Housing: https://www.health.ny.gov/regulations/nycrr/title_10/part_15/

Managing Alternaria Leaf Spot and Head Rot in Broccoli

Sue Scheufele “Can Alternaria Leaf Spot Be Managed Organically?” http://www.hort.cornell.edu/expo/proceedings/2013/Cole%20Crops/Cole%20Crops%20Scheufele%20Alternaria.pdf

Christy Hoepting “Control of Alternaria head rot in broccoli featuring exciting results from 2018 on‐farm fungicide trial” http://www.hort.cornell.edu/expo/pdf/20190115-all-day-hoepting.pdf

Dropped Covered Produce:
FDA Factsheet on Dropped Covered Produce: https://www.fda.gov/media/129568/download

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