All four projects are funded with a special allocation from the state legislature in 1998 linked to a bill (AB 1998) promoting the development of alternatives to methyl bromide, sponsored by Assemblymember Helen Thomson (D-Yolo County) and administered through the Department of Pesticide Regulation. One of the four projects also receives funding from the Biologically Integrated Farming Systems (BIFS) ag chemical use/risk reduction program. The BIFS program was the original funding target of Thomson’s bill.

Methyl bromide is often used as a pre-plant fumigant to eliminate nematodes, weeds and pathogens in agricultural systems such as strawberries and orchard crops including almonds, walnuts and stone fruits; it is also commonly used as a postharvest treatment to control insect pests. Methyl bromide is designated a Class I ozone depleter scheduled for a 100 percent use reduction in the U.S. by 2005. More than four million pounds of methyl bromide were applied to strawberries in California in 1998.

“We’re pleased at the progress of the projects specifically targeting methyl bromide alternatives, and the more general demonstration effort aimed at ag chemical use/risk reduction called Biological Agriculture Systems in Strawberries, or BASIS,” Swezey says.

Swezey also notes that there is added impact due to some cooperation among the four SAREP-funded strawberry projects. Some researchers are cooperating on component work in UC test plots and nurseries, while BASIS participants are incorporating recent work into their demonstration plots on farms.

Dave Riggs, president of the California Strawberry Commission, is pleased to see the four strawberry projects underway. He has been particularly supportive of the outreach effort that is part of the BASIS project, whose demonstration plots are located in Santa Cruz and Monterey counties.

“We’re particularly gratified by this project of biologically oriented solutions integrated into the matrix of conventional farming,” he says.

Carolee Bull, principal investigator for the BASIS project and a research plant pathologist at the USDA Agricultural Research Service office in Salinas, notes that the project management team now includes herself and two UC scientists, an outreach coordinator, two research managers, three grower members, two pest control advisors and two ex-officio members from the California Strawberry Commission. The project also has added an industry partner, Soil Technology, which is providing materials for some of the below-ground research sites and is working with the team to have the products useful in organic systems registered by Organic Materials Research Institute (OMRI).

“The mycorrhizal inoculant we are using as part of the biological system stimulates plant growth and can control some soilborne diseases, and is now registered thanks to our industry partner,” Bull says.

Bull’s team is demonstrating and studying insect, weed, pathogen, fertility and soils management options in strawberries and evaluating possible new techniques to add to the alternative farming system.

“With this approach we hope to provide growers with biological tools to help them manage their pest problems,” she says. “We’re using mentor growers to showcase farms which employ innovative biointensive management strategies. These farms are demonstrating the BASIS template.”

In the fall of 1998 the BASIS team established three field plots with biologically based systems for control of soil-borne diseases and weeds including soil solarization with tarps and broccoli residues, and five field plots for insect control, including the use of trap crops to concentrate insect pests. So far the biologically based system for the control of weeds provides 50 to 70 percent control compared to 100 percent for methyl bromide and Vapam.

Team members have discussed their work at several field days and have signed on new growers. In addition to developing the BASIS template, Bull reports that significant progress has been made in developing an organic agriculture template called OASIS (Organic Agriculture Systems in Strawberries) and is enrolling organic strawberry producers. The 1999-2000 field season has seen the number of acres enrolled in BASIS double for conventional production and more than double in organic production.

“Many larger growers are curious about organic production,” Bull says. “We hope the increased number of organic acres now part of our study will help answer some of the questions they have.”

Bull says survey results from the 1997-98 season are serving as the baseline reference point for evaluating the project’s progress and performance. Baseline data will be compared with the pesticide use data gathered from BASIS and OASIS plots this year.

“We’re happy team members are interacting with growers, and now we’re seeing the BASIS program begin to integrate its multiple components,” she says.

UC Davis plant pathologist John Duniway is directing a project aimed at finding soil microorganisms to improve root health, growth and yield of strawberry plants without methyl bromide soil fumigation, which can be integrated with other cultural, biological and chemical treatments.

“While no individual microorganism or combination of beneficial microorganisms is likely to reproduce the large yield increase we get with methyl bromide and chloropicrin fumigation of the soil, inoculations with specific microorganisms [to stimulate growth] are likely to increase yield significantly,” Duniway says.

Duniway’s team evaluated four different species of bacteria and several application regimes in inoculation trials at the Monterey Bay Academy site in Watsonville.

“Since we’ve just begun to pick fruit to determine yields in early April, differences among these treatments are still small,” he says. He notes that the bacterial treatments found to increase yields in greenhouse trials so far do not appear to increase yield when used alone in the field, but in combination with a low dose of chloropicrin they increased growth significantly.

Duniway says preliminary results from his tests at the UC South Coast Research and Extension Center in Irvine are similar.

“At Irvine we inoculated with three different bacteria using both plug plants developed by Kirk Larson [a principal investigator on another project mentioned in this article] and bare root transplants,” he says. He notes that growth and yield differences through March were small, and so far only fumigation treatments have increased yield.

“We are continuing to screen additional bacteria for beneficial effects on strawberries in the greenhouse,” he says. “Some of our recent isolates show considerable activity.”

Currently, the most economically feasible alternatives to methyl bromide for strawberry production are other chemical fumigants, Duniway notes, but most are less effective or more variable than methyl bromide and all have risks and some do not have full registration or public acceptance.

“Nonchemical approaches are needed to supplement chemical alternatives or possibly replace them in the longer term when used in integrated systems,” Duniway says. “Introducing beneficial microorganisms with transplants is one such approach that warrants research for strawberries, especially since the method can be combined with current practices and, in the future, with other approaches into less pesticide-intense systems.”

Duniway says that the results obtained so far show some of the potential benefits and pitfalls of using biological agents to help replace methyl bromide. Inoculations with bacteria were beneficial only in combination with a low level of a chemical fumigant, while most of the inoculation treatments alone attempted in the field this first year were not beneficial.

“Clearly, these results are very preliminary and more research needs to be done to know if and when beneficial bacteria might be used to advantage in commercial strawberry production,” he says.

In the 1999-2000 production year, California farmers planted 600 million bare root strawberry transplants. Annual plantings of pathogen- and pest-free transplants have been the basis for high productivity and successful strawberry integrated pest management (IPM) programs for decades. These “clean” bare root transplants are produced in a process that includes at least three field propagation cycles, with preplant soil fumigation used in advance of each cycle. Currently, strawberry nurseries fumigate with mixtures of methyl bromide and chloropicrin to ensure the production of pathogen- and nematode-free transplants.

One of the SAREP-funded methyl bromide alternative projects is determining the potential for using containerized strawberry transplants to produce pathogen- and pest-free planting stock in soil-less media, thus eliminating the need for methyl bromide soil fumigation. This research is evaluating the potential to make a major change in the way strawberry planting material is produced with possible reductions in the use of the ozone-depleting methyl bromide.

Kirk Larson, an associate pomologist and associate UC Cooperative Extension specialist at UC Davis, is working at the UC South Coast Research and Extension Center in Irvine and other locations in the state to develop suitable methods for propagating and conditioning strawberry plugs under California conditions. Larson is also evaluating plug performance in the state’s major strawberry production regions. Although strawberry plugs are used in other parts of the U.S., there is little information regarding propagation and use of plugs for strawberry production in California.

Larson and co-investigators conducted strawberry plant propagation research using disease-free, soil-less media in a commercial nursery in Redding during the 1999 propagation season. Despite the preliminary nature of the results obtained so far, it is possible to draw certain conclusions, he says.

“There appear to be clear benefits to yield and fruit quality by growing strawberry plug plants in a high elevation,” he says, “Also, plug plant age appears to have significant effect on fruit production, with the older more mature plugs outperforming younger plug plants.”

Larson says neither result is entirely unexpected, as the benefits of runner plant age and high elevation propagation have been shown before, however, in the conventional bareroot production systems the information is crucial to make this new system work.

Larson confirms what many home gardeners have found to be true: It’s not hard to propagate strawberries. Take a cutting from a strawberry plant runner, put it in the ground, and it will tend to grow and produce, he says.

“The key is the quality of the plant and the fruit,” he says. Quality is the critical variable for California strawberry growers as they compete with other California growers and with strawberries produced in Florida and other locations. “It’s important because the market is very competitive, except maybe in December when consumers will buy anything red,” Larson adds.

Larson is conducting field trials in test plots in Irvine, where he is testing 17 plug treatments in replicated plots. He is looking at results when plugs are different ages at planting, when different container sizes are used, and when plugs are conditioned at different nursery locations (in MacDoel, or in Redding either on benches in a nursery or stored in coolers at night to try to replicate higher elevation conditions).

He notes that while productivity is important, quality has always been the stumbling block.

“Plug plants can produce large amounts of fruit, but the fruit quality is often inferior-small and misshapen,” he says.

Thus far, his results show that achieving fruit quality from plug plants is going to involve some kind of conditioning for the plugs at high altitudes and latitudes. His trials have taken place at MacDoel, which has an elevation of 4200 feet at the Oregon border, and in coolers in Redding.

He says the shorter days and cooler nights beginning in late summer in high elevation nurseries somehow lead to strawberry plugs that have higher yields and quality. Larson tried to duplicate these natural conditions in Redding by putting the transplants into coolers at 4 p.m. daily beginning in early September.

“We were hoping that our coolers would duplicate the outcome,” he says, “but we weren’t very successful in mimicking the total high elevation environment.”

Larson says he is targeting two main variables in this research: 1) the location (elevation, temperature, daylight hours) of the nursery, and, 2) the timing/mechanics of the propagation system.

Regarding the mechanics of the propagation system, Larson says the main variable appears to be plug age, with plug container size having less of an effect. He used plug plants that varied from six to 10 weeks in age; older plugs tended to out perform the younger plants.

“We need to produce a more mature plug plant by September, which probably entails starting the mother plants in April rather than May,” he says.

Larson notes that turn-around time and space for plants with long runners is an issue for commercial plant nurseries. “We’re learning a lot about the ins and outs of this system and we’ve made a lot of progress,” he says. “We know it is important for the use of plug plants to remain cost effective, which is part of my task.”

His plans for the next season include cutting the runner tips earlier in the propagation cycle, so they can have a month to six weeks of high elevation conditioning.

Elizabeth Mitcham, an extension specialist in the UC Davis Department of Pomology, is the principal investigator in a project focusing on the possible use of acetaldehyde and carbon dioxide rather than methyl bromide as fumigants to control insects on harvested strawberries. Developing postharvest alternatives to methyl bromide is critical for California’s growing export market, as the chemical is used for quarantine control of insects on fruit exported to Japan and Australia.

“We’re trying to determine the effectiveness of acetaldehyde fumigation alone and in combination with carbon dioxide to kill western flower thrips and two-spotted spider mites,” Mitcham says.“We have preliminary data that looks interesting, but we need more work.”

Mitcham says experiments so far have shown that if the levels of acetaldehyde are too high, in addition to killing insects it can give “off” flavors to the strawberries. “However, the right amount of acetaldehyde enhances the aroma of the fruit,” she says. “It increases the amount of volatile compounds, which is where the aroma comes from, and can make a big difference in the aroma.”

Mitcham says that even though acetaldehyde is a natural compound, because it would be used in higher concentrations then would naturally occur in the fruit, its safety would have to be checked. “It might be a ’Generally Recognized As a Safe’ [GRAS] compound, but that remains to be determined,” she says.

Tests with thrips and mites exposed to acetaldehyde at the same levels that were not damaging to the fruit look promising for pest control, she says.

“However,” she says, “when we put the fruit and the pests and the same level of acetaldehyde together, the fruit absorbs the acetaldehyde so quickly that there is not enough left for good insect control. Now we’re testing insect mortality with the fruit present to see if there’s a different strategy to use to get insect control without damaging the product.”

“It’s been a fun project and we’re guardedly optimistic,” she says. “We’re not home free, but we still think it has a lot of potential.”

If successful, this treatment could provide consumers with less chemical residues and potentially enhanced flavor and aroma. This approach could also be used for other commodities, Mitcham says.

“We experienced a learning curve in methodology development,” she says. “Our early work with acetaldehyde was much more variable and difficult to interpret. Improvements in methods and techniques have removed most of this variability, and some of the earliest work will be repeated. We’ll also look at the effects of CO₂ with acetaldehyde on both insect mortality and fruit tolerance in more depth.”

Practical Help

Reggie Knox, a cooperator on the BASIS project from the Community Alliance with Family Farmers, is pleased to see the four SAREP-funded strawberry projects underway.

“Strawberry growing is very complex and tremendously capital-intensive, costing growers $25,000 to $30,000 per acre in labor and inputs,” he says. “So it’s easy to see the challenges in replacing a product like methyl bromide, which has been very effective in getting yields up, or in experimenting with an approach that looks at the entire farming system.”

“When we’re starting to look at a biological system in strawberries there are a tremendous amount of variables, whether it is below-ground doing inoculant trials with mycorrhizal fungi to stimulate growth, or above-ground looking at different trap crop plants to concentrate destructive pests like lygus,” he says. He notes that the partnerships of scientists and growers in the strawberry projects are important in finding solutions for the industry.

Dave Riggs, Strawberry Commission president, is glad research priorities are aimed at practical help for growers.

“The strawberry commission has been looking at methyl bromide alternatives for many years,” Riggs says. “Thirty years of work has given us a good understanding of alternatives that exist, but the SAREP grants allow us to go beyond what is currently available to offset the loss of methyl bromide.”

Additional methyl bromide alternatives projects funded by SAREP, “Cultural Control and Etiology of Replant Disorder of Prunus spp.,” Greg Browne, Russell Bulluck, Tom Trout; “Development of Grape Rootstocks with Multiple Nematode Resistance,” Howard Ferris; and “Alternatives to Methyl Bromide for Control of Soil-borne Fungi, Bacteria and Weeds in Coastal Ornamental Crops,” James MacDonald, Clyde Elmore, Steve Tjosvold, will be described in the next issue of Sustainable Agriculture (Volume 12, No. 3).