Research for MeBr Alternatives May Benefit Organic Growers

The Agricultural Research Service’s methyl bromide alternative research program is investigating a wide range of approaches to replace methyl bromide. Many of these may fit well with organic farming practices. Because of that, organic growers could reap benefits even though the research may not be specifically directed toward helping them.

Even though efforts to research chemical alternatives still continue, ARS and other institutions are also focusing research on finding cultural and biological alternatives that organic farmers can put to use. For example, Dan Chellemi with ARS’ U.S. Horticultural Research Laboratory in Fort Pierce, Florida, is working on soil solarization systems that could be incorporated into conventional or organic vegetable production systems to help control nematodes and weeds. While soil solarization has long been used by organic growers, Chellemi has developed ways to improve the technique by incorporating organic amendments to create an effective nonchemical alternative to methyl bromide.

Working with Vero Beach, Florida, organic grower Kevin O’Dare, Chellemi has been testing a combination of manures and recycled yard materials added to the beds. The beds are then wet down before they are covered with clear plastic to start the solarizing. “The organic amendments encourage the buildup of beneficial microbes,” Chellemi says. “And as this compost-soil mixture heats up, it produces gases—primarily methane—that displace soil oxygen. As a result, weeds are unable to germinate.” The organic amendments could also be used alone, but Chellemi believes some sort of combination will be the most effective control.

O’Dare claims that using Chellemi’s system of organic amendments and solarization has saved his business. “I can’t say enough for it,” O’Dare says. Purple nutsedge was close to taking over the ten acres of his Osceola Organic Farm, and would have been difficult to control even with chemicals. By O’Dare’s second year of solarization, production was up 30 percent, labor was down 75 percent, and profits were up 100 percent. O’Dare’s ten varieties of lettuce, tomatoes, peppers, squash, eggplant, and culinary herbs require less water and fertilizer with Chellemi’s system. “It’s a very sustainable system,” O’Dare says.

Jim Stapleton, an integrated pest management plant pathologist with the University of California, has also been looking at combining soil amendments and solarization as an alternative to methyl bromide for vegetables, ornamentals, and strawberries. His approach is essentially the same as Chellemi’s, but he is developing the biologically based technique to work in an arid, desert environment instead of a humid, subtropical climate.

“The trick we need to figure out to make the system work for conventional farmers is how to tailor soil amendments to specific crops,” Stapleton says. He is experimenting with a variety of crop rotations and amendments that best suit his climate and the economics of the region.

Many large farmers in California are committed to an intensive production schedule, growing two or three crops a year on the same land. Some crop sequences are more likely to result in fewer soil pests. “The residue of one crop can keep down the pests of the next crop if you use the right sequence,” Stapleton explains.

Organic farmers have been quicker to adopt the solarization and soil amendments techniques. “It has been really easy working with organic growers to test the new systems—they pick it up and run with it,” Stapleton says. “It is harder for corporate farms to convert to knowledge-based systems like solarization and tailored amendments because the work on such large farms is more partitioned—with a separate irrigation person and a pest manager and all the rest. Everyone has to accept the new idea and decide to apply it. The small organic farmers make all or most of their own decisions. If they buy into a new strategy, they can institute changes almost immediately,” he says.

And methyl bromide has worked so well for so many years, there has been no impetus for non-organic growers to look for alternatives. “Now, with the ban coming, other farmers are more willing to look at techniques that organic farmers have been quicker to adopt because they had to have something besides chemicals,” Stapleton adds.

Stapleton is also working on the problem of producing clean nursery stock for farm planting without the use of methyl bromide. The California Department of Food and Agriculture recently accepted a protocol he developed using solarization to kill nematode and fungal pests in soil and containers that are then used to raise clean nursery stock. Solarization can be used to bring the soil to a temperature of 70° C (158° F) for at least 30 minutes, under the new regulation. Stapleton is currently looking at the effectiveness of lower temperatures, such as 60° or 65° C, for longer periods of time.

Soil solarization is not optimal for strawberry nurseries in California because many of them are in northern California at high elevations, where it is too cool to depend on the sun for solarization, Stapleton points out. He is looking at the potential for using artificial heat sources to produce clean nursery stock. “But a containerized system is going to be easier to disinfect than trying to do it in a field situation,” Stapleton says.

Jim Cochran, an organic strawberry grower in Santa Cruz, California, has been using organic farming methods for 15 years. He uses crop rotation systems with crops such as broccoli and cauliflower, along with soil amendments. “I hope researchers can find effective methods that can be used by organic farmers,” he says. “But I don’t expect any magic results within the next couple of years. Organic farming is a complex system that requires a long-term commitment.”

Cochran also agrees with Stapleton’s point that, in some cases, farmers have been moving much faster than researchers when it comes to biological alternatives to methyl bromide. “Many major growers in our region have moved large blocks of prime farmland into organic production, but the research community continues to spend only a tiny percentage of its resources on nonchemical research,” he says. He hopes that researchers will look at a broad systems approach and try to understand soil biology and that more cooperation between farmers and researchers will result in new and more effective farming methods.

One of his most important concerns is what will happen to nursery stock with the loss of methyl bromide. Organic growers, like all growers, depend on certified nursery stock, which is currently grown with the help of methyl bromide to be disease and pest free. “I have some ideas on alternative methods that use a sterile medium and manipulation of temperature and day length,” he says. “The problem is that my ideas are expensive.”

ARS plant pathologist Carolee Bull, at the Crop Improvement and Protection Research Unit in Salinas, California, has been focusing on biologically integrated cropping systems for disease control. “We have developed an integrated research program that involves farmers and other scientists in multidisciplinary approaches to the problems that face our local farmers,” says Bull. The lab is working on several projects involving organic agricultural systems that could be alternatives to methyl bromide use.

One of Bull’s most significant projects is the BASIS-OASIS (Biological Agricultural Systems in Strawberry-Organic Agricultural Systems in Strawberry). “Our goal is to develop a set of biological approaches for growers to use in addition to their current management practices,” Bull says. The interdisciplinary project is funded by the University of California Sustainable Agricultural Research and Education Program (SAREP) and involves the efforts of farmers, plant pathologists, weed scientists, entomologists, soil scientists, and erosion control specialists. Biological approaches, including bacterial biological control agents that were developed for conventional farming, are being tested in organic systems. Research includes the enhancement and release of beneficial species such as soil inoculants, beneficial predatory insects, insectary plants, nonchemical weed control methods, trap cropping, and erosion control methods.

SAREP associate director and lead scientist for the methyl bromide alternatives grants program at the University of California, Jenny Broome, who is funding Bull, points out that “instead of replacing one chemical with another, farmers learn from other successful farmers and from researchers about biological farming systems that are less reliant on chemical controls.” The project is still in its first year, but researchers hope it will provide lasting benefits to the strawberry industry.

Bull and her team are also trying to determine what role plant pathogens may play in the lower yields reported in organic production. They are evaluating biological control agents for their ability to increase growth and yields in nonfumigated soils. Among the tested agents are commercially available inoculants as well a mychorriza isolated from the strawberry rhizosphere. “We have found agents that increase plant growth and yield,” Bull says. “The difficulty is extrapolating from a conventional production system to an organic system.” These agents may be useful to the organic industry if the companies marketing the products are interested in pursing OMRI [Organic Materials Review Institute] registration.”

Specifically helping organic farmers was not in ARS plant physiologist Aref Abdul-Baki’s mind when he began developing a basically nonchemical production system for fresh-market tomatoes, using hairy vetch as an organic mulch. But his system has proved so successful in the mid-Atlantic region that he is now collaborating with scientists and officials in Florida and California to tailor a version of the system for winter tomatoes and other vegetables that can combat root-knot nematodes. These nematodes are one of the major problems faced by tomato producers in south Florida and southern California.

Abdul-Baki’s system integrates a number of cultural choices, including growing nematode-resistant cover crops such as cowpea varieties, white clover, and sunn hemp; selecting nematode-resistant tomato cultivars such as Sanabel and Sunjay; and each planting season rotating with crops that are not hosts to nematodes, such as wheat, rye, and sorghum, followed by tomatoes. He is currently finishing the first year of testing to find the most effective cover crop for subtropic regions.

“A single change that is as effective as methyl bromide is almost impossible,” says Abdul-Baki. “While no one approach is likely to lead to effective control of all nematodes, integrating several cultural practices into one alternative production system could result in an effective approach. Vegetable and cover crop cultivars can be rotated to reduce the incidence of soilborne pathogens and populations of root-knot nematodes,” he says.

Last Updated: October 1, 1999