Treated Wood in Organic Farming Frequently Asked Questions

Let's begin with the bad news: MOSA does not know of any commercially available wood preservation treatments that are allowed for direct contact with organic crops, livestock, or soil. Nor are there any on the approved inputs lists from the two main third-party organic material review agencies, the Organic Materials Review Institute (OMRI) and the Washington State Department of Agriculture (WSDA). There is, though, plenty still to discuss in this article about treated wood, including which treatments are less prohibited (and toxic) than others, effective intervention strategies to protect organic products from contact with wood treatments, and uses of treated wood on organic farms that are acceptable.

Let's begin with a very brief history of chemical wood preservation in the US. By the middle of the twentieth century, three heavy-duty wood preservatives had been developed for lumber installations in the US to resist decay and insects:

Creosote, obtained from coal tar and used in industrial applications like railroad ties and utility poles;
Chromated Copper Arsenate (CCA), a blend of copper, arsenic, and chromium that was pressurized into lumber for outdoor residential and industrial uses;
Pentachlorophenol (Penta), a petroleum-based herbicide and mossicide used in industrial applications, mainly utility poles.

But by the end of the twentieth century, a host of environmental and human health concerns regarding these three chemical compounds had been researched and documented: chemicals leaching into soil and groundwater were toxic to plants and aquatic animals years after installation, off-gassing fumes contributed to human respiratory diseases, and all three directly exposed people to deadly carcinogens.

Early in our current century, the US Environmental Protection Agency and the manufacturers of the three toxic preservatives agreed to restrict the use of the treatments to non-residential, industrial, and agricultural uses. For residential lumber, the industry stopped using CCA by the end of 2003 and pivoted to several water-based, less toxic compounds. However, the EPA continues to allow agricultural use of certain CCA-treated lumber types: plywood, fenceposts, and laminated building columns.

When the USDA's National Organic Standards were issued in 2002, the crop pest control standard (205.206) included this prohibition regarding treated lumber: "The producer must not use lumber treated with arsenate or other prohibited materials for new installations or replacement purposes in contact with soil or livestock." In 2016, the National Organic Program supplemented this directive from the Organic Standards by issuing the seven-page "NOP 5036: Treated Lumber (Draft Guidance)", which clarified some particular areas around treated wood for farmers and certifiers. For instance, the Guidance stated that use of treated wood does not delay organic transition or necessitate a new three-year transition, and the document provided examples of lumber that do and do not contact organic products.

Over the past 25 years, MOSA has used the prohibition in the Organic Standards along with the 2016 Guidance to formulate detailed responses for our staff and farmers around particular uses of treated wood on MOSA-certified organic farms. That guidance shapes the following responses to the frequently asked questions MOSA staff receive about treated wood from our organic farmers.

Q. Which wood treatments are prohibited for new installations or replacement purposes in contact with organic crops, livestock, or soil?

A. Copper chromated arsenate (CCA), creosote, pentachlorophenol (penta). Typically, this prohibits organic farmers from re-using railroad ties, telephone poles, and old pressure-treated lumber (likely treated with CCA), and excludes the use of any new CCA-treated agricultural lumber, particularly fenceposts and plywood.

Q. What if I already have lumber on my farm that contains prohibited wood treatments when I apply for organic certification?

A. The presence of treated lumber doesn't prevent you from applying for certification and doesn't require a longer transition of an affected field. You must arrive at a plan that MOSA approves for preventing the treated wood from contacting organic crops, livestock, and soil. You may want to replace the wood with less toxic alternatives if possible.

Q. Which wood treatments are considered restricted for new installations or replacement purposes in contact with organic crops, livestock, or soil?

A. Any of the newer, water-based preservatives, including ACQ (alkaline copper quaternary), Borates (Disodium octaborate tetrahydrate), CA (Copper azole), MCA (micronized copper azole, including version AC2). These newer treatments are considered less toxic than the older, oil-based preservatives, but they still consist of synthetic substances that are not allowed in organic farm production.

Q. Are there any allowed wood preservatives?

A. As mentioned above, MOSA does not know of any commercially available wood preservatives that are allowed for direct contact with organic crops, soil, or livestock, and none are listed by third-party material review agencies OMRI or WSDA. To be acceptable, the input would need to consist of all-natural ingredients or synthetic substances included in Organic Standard 205.601, the list of synthetic substances allowed for use in organic crop production.

Q. What are acceptable barriers to prevent already-installed treated lumber from contacting organic products?

A. Any inert material that prevents organic livestock or crops from contacting the treated wood, such as electric or barbed wire, or a covering of metal (without unsafe, sharp edges), fiberglass, rigid plastic, or untreated wood. Note that paint is not an acceptable barrier, since paint also consists of unnatural materials that are not on the list of allowed synthetic substances.

Q. What are some examples of lumber that does contact soil, crops, or livestock?

A. Feed bunks and hay racks, greenhouse baseboards within 2' of in-ground crops and their roots, livestock stalls, paddock fences that livestock touch, greenhouse benches if contacting plants, hay mows, plant trellises and stakes, planting boxes, watering troughs, perches for poultry.

Q. What are some examples of lumber that does not contact soil, crops, or livestock?

A. Distant pasture fence posts that do not contact cattle, orchard posts that support trellis wires but do not contact plants, trailers that do not contact crops, baseboards in greenhouses without in-ground production, equipment storage sheds, tables in greenhouses if plants and soil do not contact the wood, treated wood with an effective barrier.

Q. What are acceptable alternatives to treated lumber?

A. Posts made of metal, plastic, fiberglass, or naturally rot-resistant wood (e.g. cedar, locust, cypress, Osage orange, redwood).

Q. What are some other considerations regarding processed wood?

A. Untreated plywood is allowed in organic production unless the glued edges begin to peel or separate. Chipboard or particle board, in which the synthetic glue reaches the board surface, is not allowed for direct contact with organic crops, soil, or livestock. For in-ground production, MOSA requires a 2' distance between the treated wood (such as a hoophouse baseboard) and organic plants and their roots.

As it has in the past, the topic of wood preservatives and their compliance with the Organic Standards will continue to evolve. If you have a question about treated wood that has not been answered here, please contact MOSA's Client Services Team (844-637-2526, customerservice@mosaorganic.org). Also, let us know if you have a homemade wood preservative blend that you would like MOSA to review for you, and our Material Review Team will gladly determine if it is acceptable. Treated wood on organic farms certainly represents a corner of the organic agriculture movement where our commitment to growing feed and food without the use of synthetic, unsafe chemicals has identified a market opportunity for the development of a safe, compliant, effective wood preservative that is fully allowed in organic farming.