Popular fungicides for peach leaf curl phased-out

Two important fungicides that home gardeners have used for years to control peach leaf curl have been withdrawn from the market. Home garden uses of lime sulfur spray (calcium polysulfide) were canceled by U.S. EPA, effective Dec. 31. Another fungicide, Microcop (tribasic copper sulfate) sold by Lilly Miller, was recently discontinued by the manufacturer although existing supplies can be sold and used. As a result of these actions, home gardeners now have very limited and less-than-ideal options for treating peach and nectarine trees during the dormant season to prevent leaf curl.

Two products, Kop R Spray by Lilly Miller and Liqui-Cop by Monterey Lawn and Garden, which contain copper ammonium complex, are still available. These products only contain 8 percent copper and are less effective than Microcop, which contains 90 percent tribasic copper sulfate. Their effectiveness can be increased by adding 1 percent horticultural spray oil to the spray mix. The fungicide, chlorothalonil, is effective against leaf curl, but it is listed as a likely carcinogen and can cause severe eye or skin irritation, if the product is mixed or sprayed carelessly.

Do-it-yourself gardeners can make their own fungicide spray to control peach leaf curl by following the directions in UC Pest Note 7481, Bordeaux Mixture (do an Internet search for “UC Pest Note 7481”). The process requires buying a small quantity of copper sulfate and agricultural lime to make a stock solution of each chemical, which are then combined and diluted with water to make the final Bordeaux spray. It is very effective against leaf curl, but finding the ingredients and mixing them may be more work than some gardeners want to do to protect one or two trees.