The United States Congress recently postponed for four years a ban on the widely used fumigant methyl bromide, a chemical implicated in the depletion of the Earth’s ozone layer. The Congressional move allies US law with the Montreal Protocol, which calls for methyl bromide use to be reduced in increments, beginning with 25% less in 1999, 50% less in 2001, 75% less in 2003 and then eliminated in 2005. The action renews the sense of urgency felt by farmers nationwide for ways to maintain their economic viability in the absence of the pesticide.
Methyl bromide solves an array of problems for farmers. Applied in the field before planting, the gas kills most old plant roots, weed seeds, nematodes, soil fungi and bacteria – organisms that sap vigor from a crop. After harvest, methyl bromide fumigation can ensure that produce being shipped to markets worldwide is free of pests. When the ban takes effect, this extremely effective broad-spectrum pesticide will be replaced with a variety of alternatives. The alternatives are now being developed and the limitations of the alternatives are now being studied by an army of University of California scientists. A sampling of their research follows:
- Solarization of Strawberries Surprisingly Successful Alternative to Methyl Bromide
- Methyl Iodide can be an Effective Alternative
- "Thermal Death Database" to Help Growers Kill Pests with Solar Energy
- Destroying Old Plant Roots without Methyl Bromide
- Nursery Industry to get New Certified Methyl Bromide Alternative
- Lasers, Radio Waves Zap Microbes and Soil Bugs
- Mulch is Good Alternative in Nursery Containers
- Alternate Irrigation Practices could Save Pear Orchards
- Carbon Dioxide may Provide Alternative for Treating Harvested Fruits and Vegetables
Solarization of Strawberries Surprisingly Successful Alternative to Methyl Bromide Soil solarization worked as well as methyl bromide in the first San Joaquin Valley field trials comparing the two treatments in strawberries. UC Cooperative Extension farm advisor Richard Molinar and UC Integrated Pest Management plant pathologist Jim Stapleton found that both methyl bromide and soil solarization increased yields more than 30% over untreated plots. Because solarization is much cheaper than methyl bromide treatment, farmers stand to profit $800 to $1,000 more per acre by tapping the sun's energy instead of fumigating with the soon-to-be-banned chemical. "This is the first year of the study, so we can't go ahead and recommend soil solarization to farmers at this point," Molinar said. "But some who have observed our trials and seen the results are beginning to experiment on their own." Molinar said the San Joaquin Valley is a "perfect fit" for strawberry field solarization. Farmers can treat the soil in the heat of the summer, just in time for the traditional fall planting, and enjoy what appears to be excellent control of weed seeds and soil-borne diseases. For more information contact Molinar at (559) 456-7555, rhmolinar@ucdavis.edu. Tip by Jeannette Warnert, (559) 225-5611, jwarnert@uckac.edu.
MethylIodide can be an Effective Alternative Methyl iodide is an effective soil fumigant for such crops as strawberries, vegetables, melons and nursery products and has the potential to improve farmworker safety, according to UC Riverside scientists. "It's going to do the same job as methyl bromide, it will enhance worker safety and, from what we know of its atmospheric chemistry, its potential for contributing to ozone depletion is minimal," said Jim Sims, UC Riverside plant pathologist. Unlike methyl bromide, methyl iodide is injected into the soil as a liquid. Methyl bromide is used as a gas, which dissipates in the atmosphere more readily and is more difficult to contain than a liquid. The ozone depletion potential of methyl iodide is insignificant compared to that of methyl bromide because ultraviolet light in the atmosphere decomposes nearly all methyl iodide before it can reach the Earth's protective ozone layer in the stratosphere. "In melons the fungal disease Monosporascus cannonballus is controlled better with methyl iodide fumigation than with methyl bromide fumigation," Sims said. He also has promising data on replanting peaches into old orchards and replanting grapes into old vineyards using preplant treatment with methyl iodide. Methyl iodide is an experimental chemical which could be available to farmers in the future. The company MIF Partners has licensed the patent for methyl iodide and is working on its registration as a pesticide. For more information contact Jim Sims at (909) 787-4127, jsims@ucrac1.ucr.edu. Tip by Pam Kan-Rice, (510) 987-0043, pamela.kan-rice@ucop.edu.
"Thermal Death Database" to Help Growers Kill Pests with Solar Energy Soil solarization is one of the most promising new techniques for killing weed seeds, nematodes and fungal pathogens in warm, inland valleys or desert areas. To solarize soil, farmers cover the ground with clear plastic and allow the sun’s energy to raise soil temperature to lethal levels. However, since there can be great differences in heat sensitivity among these organisms, UC scientists are conducting experiments to identify "thermal death" calculations for different species. "We're developing guidelines that growers can use to predict when they've cooked the soil long enough," said Jim Stapleton, UC Integrated Pest Management plant pathologist. He, IPM weed ecologist Tim Prather, UC Davis weed science specialist Clyde Elmore and UC Riverside nematologist Mike McKenry first test the technique in large tanks under laboratory conditions and again under commercial conditions in the field. Eventually, growers will have an Internet-accessible database telling them how to kill off specific species of nematodes, fungal pathogens and weeds. For additional information contact Stapleton at (559) 646-6536, jim@uckac.edu. Tip by John Stumbos, (530) 754-9554, jdstumbos@ucdavis.edu.
Destroying Old Plant Roots without Methyl Bromide An outdated variety. Rootstocks not tolerant to new diseases. A simple change of heart. There are as many reasons for farmers to replace their "permanent" crops as there are farmers. Many have successfully used methyl bromide to kill, among other things, living plant roots left behind when old trees and vines are removed. The roots provide a food source to maintain damaging nematodes until the new plant roots can be attacked, severely stunting the growth and vigor of the new crop. UC Riverside’s Mike McKenry, based at the Kearney Agricultural Center near Parlier, has found a new way to destroy roots that, left undisturbed, can live underground for as many as eight years. Farmers can chop off trees or vines above the soil line, paint an herbicide on the cut trunk, then wait one year before planting. "You do lose an entire growing season, but the organisms that thrive on live roots are overtaken during that time with organisms that thrive on dead roots. Those organisms will leave the new plants alone," McKenry said. For more information, contact McKenry at (559) 646-6554, mckenry@uckac.edu. Tip by Jeannette Warnert, (559) 225-5611, jwarnert@uckac.edu.
Nursery Industry to get New Certified Methyl Bromide Alternative Early next year, the nursery industry will have a new method certified by the California Department of Food and Agriculture for preparing soil, which is now sometimes done with methyl bromide. Three scientists at the UC Kearney Agricultural Center near Parlier – UC Integrated Pest Management plant pathologist Jim Stapleton, UC Riverside nematologist Mike McKenry and UC Davis horticulturist Louise Ferguson – developed a system for solarizing soil in nursery pots. The pots are filled with planting mix, placed on a pallet and covered with a double layer of clear plastic held up like a tent by a frame or wire hoops. "The soil gets much hotter than in an open field," Stapleton said. "In the San Joaquin Valley, the soil temperature can go higher than 160 degrees." At that temperature, after just 30 minutes, the treatment is complete. Certification, expected in March 1999, will allow growers to use the method in the production of nursery plants, which by law must be guaranteed not to harbor economically important nematodes. For more information contact Stapleton at (559) 646-6536, jim@uckac.edu. Tip by Jeannette Warnert, (559) 225-5611, jwarnert@uckac.edu.
Lasers, Radio Waves Zap Microbes and Soil Bugs
Mulch is Good Alternative in Nursery Containers
Alternate Irrigation Practices could Save Pear Orchards Oak root fungus is a huge problem in many California tree and vine crops. When it gets bad enough, farmers typically rip out the crop, fumigate the soil with methyl bromide and start over. Until recently pear growers believed they were immune to the problem. However, when farmers switched from flood to sprinkler irrigation 15 to 25 years ago to increase fruit size, the disease became more common in North Coast pear orchards. Researchers at UC Davis are investigating whether oak root fungus can be managed by modifying irrigation practices. "We're trying to find a middle ground," said plant pathologist David Rizzo, who, with water relations scientist Ken Shackel, have set up an experimental pear orchard at the Armstrong Research Plots on the Davis campus. "We're trying to find a way to avoid a problem that takes a long time to get established," Shackel said. One device under study shoots out air at a high speed to blow dirt away from tree roots, allowing scientists to see the roots -- and the fungus on infected trees -- underground. Exposing the roots may alter the growing conditions enough to kill off the fungus. For more information, contact Shackel at (530) 752-0928, kashackel@ucdavis.edu or Rizzo at (530) 754-9255, dmrizzo@ucdavis.edu. Tip by John Stumbos (530) 754-9554, jdstumbos@ucdavis.edu.
Carbon Dioxide may Provide Alternative for Treating Harvested Fruits and Vegetables In addition to its use in the field, methyl bromide is used by packing houses to fumigate harvested fruits and vegetables exported to certain foreign countries and sometimes to other states. California strawberries, for example, must be fumigated before being shipped to Japan. UC Davis researchers are looking at several materials that could be substituted following the methyl bromide ban. Cooperative Extension Pomology Specialist Elizabeth Mitcham has been testing combinations of carbon dioxide at cold-storage temperatures on pests found in table grapes -- western flower thrips, Pacific spider mites, omnivorous leafroller and grape mealybug. The technique is showing promise and could eventually open international markets now closed to US exports. "The carbon dioxide treatment is pretty encouraging," she said. "But it's not the answer for everything. It fills an important niche and has the added benefit of being non-chemical." Mitcham will also be testing the technique on lettuce, asparagus and broccoli in collaboration with Cooperative Extension Vegetable Crops Specialist Marita Cantwell. For more information, contact Mitcham at (530) 752-7512 or ejmitcham@ucdavis.edu. Tip by John Stumbos (530) 754-9554, jdstumbos@ucdavis.edu.