By Island County Extension Agent, Donald B. Meehan
EPA RESTRICTS USE OF WOOD PRESERVATIVES
This year the Environmental Protection Agency designated three types of wood preservatives as "Restricted Use" pesticides. This will have an impact on many homeowners and small farmers who don't want to go to the lengths of getting a license to buy the newly-restricted materials.
The wood preservatives which will be taken out of general use next month on November 10th, 1986, are pentachlorophenol, creosote, and inorganic arsenicals. Most of us are familiar with pentachlorophenol. We generally call it "Penta". The inorganic arsenicals comprise those wood preservatives which have arsenic as a component. They are not often found available.
In order to purchase and apply any of these types of chemical pesticides, a person will have to be licensed by the Washington State Department of Agriculture. Lumber yards, farm supply stores and hardware stores will all be required to have dealer licenses to sell these products. They will be required to see documentation that a buyer has been properly licensed. Information about licensing can be obtained by contacting me.
Since people are going to find it harder to buy wood preservatives over-the-counter, many may turn to already treated lumber products. If this is the case, I would like to take a few moments to share some information about commercially-treated wood. This is an area I get a number of questions about each year.
One of the big concerns people have about treated wood is whether it will pose a health hazard to them if used in vegetable gardens and whether it will damage plants grown next to it. These are difficult questions to answer. There is not a great deal of information about the transfer of these kinds of pesticides into plants. Hence, I will not be able to address that issue very well. What I will address is the kinds of chemicals used as commercial wood preservatives.
Let's begin with "Penta" and Creosote. Both are oil-type preservatives and don't generally leach into the soil. They have a very restricted use in the commercial field. Neither of these compounds should be used in gardens or greenhouses for planting beds. Plants cannot handle the toxic fumes from these chemicals. Cuprinol, by the way, is the only wood preservative which is safe for plants, especially inside a greenhouse.
About 90% of all commercial wood treatments are pressure-type using waterborne preservatives. The advantage is that this process allows for a clean and paintable surface when done. There are no odors and the treatments will extend the life of wood for 20 years or more.
There are several types of chemicals used in these commercial pressure treatments. They are acid copper chromate, ammoniacal copper arsenate, chromated copper arsenate, chromated arsenate chloride and fluor chrome arsenate phenol. Notice that all of these compounds contain either chromium or arsenic. These metals are both poisonous, hence the use of them in a compound means the compound will be poisonous. All are water-soluble and can leach in wet soil to some degree.
As a purchaser of lumber products treated to prevent decay, how will you know what has been used? Lumber which has been treated must be marked to indicate the type of chemical and process used. It will be the rare case, if ever, that you would see the words "treated with chromated copper arsenate". What you are most likely to see or read is a trade name for their particular treatment process. Some of the more common trade names are Wolmanized, Celcure and Chemonite. All of these processes use either chromium or arsenic compounds, which are excellent fungicides.
There is a way to differentiate which chemical treatment, but you need to have access to a guide for interpretation. If the lumber is properly labeled, it will have letters such as CCA stamped on the product. This indicates that Chromated Copper Arsenate was the chemical.
The University of Wisconsin-Extension has developed a publication which helps you sort out what the letters mean. It is called, "Preservative Treatment of Wood for Farm Use". A copy can be obtained from our office for a small fee.
Return to Articles Index
Return to Garden Page
Providing Educational Support to the Island County Community