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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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Lorsban is Banned: What Now?

Cabbage maggot (CM) feeds on brassica seedlings by tunneling into the stem of the plant just below the soil line. Their feeding can result in unsightly and unmarketable produce in the case of root brassicas like turnips, and in stunting, reduced stand, and reduced yield in head and stem brassicas like cabbage and broccoli. Lorsban and other formulations containing the active ingredient chlorpyrifos were the first line of defense for control of cabbage maggot in several brassica crops, because 1) at ~$10 per acre, it was affordable, and 2) it was easy to apply and avoided worker exposure as a directed spray at the base of the plant.

Unfortunately, Lorsban and all of its generic products for food and feed uses were banned in New York as of July 31, 2021, and in the United States as of February 28, 2022. In the absence of Lorsban and other chlorpyrifos-containing insecticides, NY brassica growers have 6 products belonging to 4 chemical classes available to manage cabbage maggot. This article, Lorsban is Banned: How to Control Cabbage Maggot in Brassicas Now?, written by Cornell Vegetable Program Specialist Christy Hoepting and Brian Nault of Cornell AgriTech, provides our "2022 Top Picks" to use instead of Lorsban plus results of Cornell research trial results related to application method, rate, and cabbage maggot control.


Propagating Strawberry Plants Through Runners

The production of strawberry plants is challenging due to the rigorous sanitation needs that must be met, especially in field propagation settings, but also in greenhouse settings. To add to that, growers in New York may find it more difficult to obtain their preferred strawberry varieties in the coming years, as fewer nurseries are propagating strawberries. The solution: strawberry plug plants propagated from runners in a controlled environment such as a greenhouse or high tunnel.

Plug production of rarer varieties that do well in New York State will fetch a higher price than dormant bare-root plants due to the higher cost of production and lower availability in the Northeast, especially if plants are available in August. Propagating Strawberry Plants Through Runners, written by Anya Osatuke of CCE Harvest NY and Brad Bergefurd of The Ohio State University, only discusses production and marketing potential of plug plants because successful field production of bare-root strawberries is very difficult to achieve without the use of highly restricted soil fumigants. 



Cornell Commercial Vegetable Guidelines Available

The 2022 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.

Cornell Crop and Pest Management Guidelines are available as a print copy ($43.50), online-only access ($43.50), or a package combining print and online access ($61.00). Shipping charges will be added to your order. Cornell Guidelines can be obtained through many local Cornell Cooperative Extension offices (call to confirm availability), or from The Cornell Store at Cornell University or call (844) 688-7620.


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