Expert: Deborah J. Meier, Ph.D., Technical Development, Kocide LLC

Growers have heard that copper rates are being reduced by regulators around the world. The US EPA just published its proposed guidelines for reducing copper use rates for many crops, including some tree nuts. What does this mean for California tree nuts?

Answer: Copper products have been a mainstay of IPM programs for tree nuts (and many other crops) for years. In fact, copper products have been used for hundreds of years to provide protection against bacterial and fungal diseases. The concern regulators around the world have is related to ecological risks, not danger to humans (copper is necessary for all living creatures). The regulatory concerns about crop use include accumulation in soil (especially on perennial crops), increased copper levels in run-off waters, and effects on fish, soil microbe and invertebrate populations.

Most ecological risks are mitigated through label language and directions for use.  The EPA is proposing to reduce maximum annual copper use for three nut crops: walnuts, pecans and hazelnuts. In California, walnuts will be the nut crop affected the most by the new proposed rule (almonds and pistachios are not of concern with respect to rates). The maximum annual metallic copper use rate for walnuts will be reduced from 32 pounds to 24 pounds per year. It is proposed the pecan use rate be reduced from 8.4 pounds to 6.3 pounds and hazelnut from 24 pounds to 18 pounds per year. Additionally there will be proposed changes made to labels regarding drift management. Label changes may be implemented in early 2019 if the EPA adopts the proposed new rules.

Growers will need to carefully select the copper product they use to make sure they have enough metallic copper to use in a season, especially if environmental conditions are conducive for disease. Walnut blight, caused by the bacterium Xanthomonas arboricola pv. juglandis, is the predominant pathogen that can reduce yields in walnuts. Copper is one of the few active ingredients that is effective at reducing this yield-robbing disease. Walnut growers typically spray 3 to 6 times per year. It is recommended that copper be tank-mixed with mancozeb.

Kocide^® products with their advanced formulation technology provide growers with ideal choices for walnut blight control. Under the new proposed regulations - Kocide^® 3000 could be sprayed 11 times per year if using the maximum single use rate of 7 pounds each time it is sprayed. Kocide 3000 provides walnut growers with a tool that provides peace of mind for walnut blight, because they won’t have to be concerned with the number of times it is used (it is hard to imagine there would be a need to spray more than 6 to 8 times even in extremely wet years). Growers often use less than the maximum copper rate when they are tank mixing with mancozeb. This combination is recommended to achieve maximum disease control (especially in orchards where copper-tolerant races are known). Kocide 3000 provides more disease control with less copper, thus less copper per acre is applied per year, which reduces copper accumulation in the soil.    

I address how to figure out copper rates based on the active copper ion in the Dec. 7 issue of Ask the Expert.