Question of the Week
I am starting an organic peach orchard. What are the disease and pest concerns associated with growing peaches? Is it acceptable to paint the trunk with white latex paint mixed with copper sulfate to prevent fungus from infecting the tree?
Answer: All the answers you are looking for are contained in the ATTRA publication Peaches: Organic and Low-Spray Production, available at https://attra.ncat.org/attra-pub/summaries/summary.php?pub=6. This publication covers all major (and most of the minor) pests and diseases of peaches and their control using organic methods. Geographic location and climate play a particular role in the incidence and severity of peach diseases and pests. Commercial scale production of organic peaches in the eastern U.S. is very, very difficult; in fact, it is virtually non-existent. As you read the entire publication and pay special attention to a couple of add-ons at the end of the publication, "Postscript: The Peach Problem and Local Food" and "Appendix I: Hypothetical Pest-Control Calendar for an Eastern Organic Grower."
Regarding the "Hypothetical Pest-Control Calendar for an Eastern Organic Grower," note that a cost analysis of such a program was not included. For this there are a number of reasons but, suffice it to say, it would almost certainly be considerably expensive given the usual high cost for some organic pest and disease controls. You would almost certainly have to get an organic premium for the fruit in order to recoup the costs of production.
Another thing to pay special attention to in the publication is post-harvest control of brown rot (and other rots) on the fruit. Currently, this is difficult for organic peach growers in the West, but it would be of paramount importance to someone in the East where disease pressure is more intense. Perhaps the most important post-harvest factor for an organic peach grower to consider is speed; i.e., get peaches cooled down and to market as quickly as possible after harvest.
Latex paint is not allowed in certified organic production because it is considered "synthetic." Copper fungicides, in general, are allowed in organic production but be sure to check with your certifying agent to find out which formulations and brands are registered for organic production. Not all are. I'm not positive which disease you're trying to control on the trunks with paint and copper, but I'm relatively certain you're talking about bacterial canker. The evidence for control of bacterial canker with copper is mixed, some studies indicating that it is only of minor or no help. The white paint is used to reflect the winter sun shining on the south and southwest facing parts of the trunk; otherwise, the winter sun warms up those sides and then subsequent freezing can cause bark cracking, which then becomes the infection site for the causal organism, Pseudomonas syringae. The best organic alternative I would recommend is homemade whitewash (see http://homeguides.sfgate.com/homemade-whitewash-trees-30913.html for an online recipe). Do not use any paint with petroleum distillates (e.g., paint thinner, kerosene) as it can penetrate the bark and kill live plant tissues.
Finally, I'd like to urge some general caution. One of the foundational strategies for disease and pest control in annual crops is crop rotation, something that you can't do with perennial fruit crops. Indeed, a disease like brown rot builds up in the orchard if you're not extremely careful, and you can't rotate out of it. On the other hand, peaches are one of the most precocious of the tree fruits, often setting fruit the second year after planting, so you should be able to figure out relatively quickly what you're going to be up against. With peaches, experiment with a small planting first and don't get fooled by the first fruiting year, the so-called "honeymoon year" because it's before the pests and diseases have found the peaches and settled in.
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