NEWS OVERVIEW: Researchers develop alternatives to methyl bromide fumigation

Abstract

finding alternatives to News overview Researchers develop alternatives to methyl bromide fumigation T Brad Hanson ime is running out for California grow- ers who still use methyl bromide. This soil fumigant is just short of a miracle for pest management — a single treatment before plant- ing controls nematodes, diseases and weeds. But methyl bromide is also a health and environmental hazard, and is being phased out under an inter- national ban. To help growers make the inevitable transition, UC and U.S. Department of Agriculture (USDA) researchers just spent 5 years testing methyl bromide alternatives for key western crops with a $5 million grant from the USDA. The program’s research is presented in the current and the coming October–December issue of California Agriculture. “One goal of the program was to identify methyl bromide alternatives that were immediately use- ful and economically feasible,” says Greg Browne, a USDA plant pathologist at UC Davis who was project coordinator for the research program. “Another was to foster development of non-fumi- gant strategies for managing soilborne pests.” Growers have used methyl bromide since the 1960s to effectively sterilize fields before planting. But this toxic gas is so volatile that more than half of the amount injected into soil can eventually end up in the air. When methyl bromide rises high in the atmosphere, it contributes to thinning of the ozone layer (the layer that shields us from ultravio- let radiation). In 2005, developed countries banned methyl bromide under the Montreal Protocol, an international treaty signed in 1987 to protect the stratospheric ozone layer. Even so, the treaty still allows limited use of methyl bromide in certain cases today. These in- clude critical use exemptions for strawberries, almonds and other crops that lack alternatives that are both effective and affordable, as well as quar- antine and preshipment exemptions for rootstock, Alternative fumigants such as 1,3-D may be the best option in the short term for nursery stock, which must be completely nematode-free to meet California’s phytosanitary certification requirements. bulbs and other nursery crops that could spread pests to new places. This authorized use shrinks each year, however, and will soon end. In the United States, recent methyl bromide use is down sharply from the 1991 baseline of 28,000 tons. The nationwide exemption for 2013 is 2.2% of baseline, or about 620 tons, and in 2014 this will drop further to 1.7% of baseline, or about 480 tons. The exemp- tion for 2015, if any, is unknown. For comparison, California alone used 3,550 tons of methyl bromide in 2004, the year before it was banned. Other restrictions on methyl bromide use in- clude seasonal bans to cut air pollution, and the requirement of buffer zones to protect people’s health. While methyl bromide depletes the protec- tive ozone in the stratosphere, it adds to ground- level ozone or smog. Thus, its use is prohibited during the warm months in parts of the state with poor air quality, including the San Joaquin Valley and Ventura County. Moreover, methyl bromide– free buffers are required around sites that are hard to evacuate, such as schools, hospitals and jails, because high concentrations of this fumigant can cause lung, eye and skin damage as well as respira- tory and central nervous system failure. Finding alternatives Most of the dwindling U.S. methyl bromide allotment goes to California and Florida, so the USDA Agricultural Research Service launched twin research initiatives to help find alternatives for growers in these regions. “The programs focused on the most important needs in the west and south- east,” says Browne. “The crop mixes were based on the views of growers and other stakeholders.” The western program, called the Pacific-Area Wide Integrated Methyl Bromide Alternatives Program, includes production crops such as grapes, strawber- ries and tree nuts as well as nursery crops such as cut flowers, forest trees and sweet potatoes. The South Atlantic Area Extension Program for Methyl Bromide Alternatives, the southeast program, in- cludes crops such as strawberries, tomatoes, cucum- bers and peppers. Finding alternatives is a challenge because methyl bromide sterilizes soil so well. “Methyl bro- mide is a one-shot control. It does so much that it’s hard to find a true replacement,” says Brad Hanson, a UC Cooperative Extension (UCCE) weed special- ist at UC Davis. In addition, the best alternative varies, depending partly on the primary benefit a particular crop gets from methyl bromide. For ex- ample, the biggest problems for production crops may be diseases or weeds. But the biggest problem http://californiaagriculture.ucanr.edu • JULY–SEPTEMBER 2013