Conventional growers can use a pesticide spray on the trap crops, but that’s not an option for organic growers. However, tractor-mounted vacuum units known as “bug vacs” are one of the tools available for organic systems. “I worked on research of the original proprietary bug vacs for the strawberry industry back in the late 1980s,” recalls Swezey. “But back then we were using more of a shotgun approach, vacuuming all of the crop fields, which in a way was equivalent to using a pesticide because it affected all the insects in the fields—both pests and beneficials. This seemed to me to be as non-selective as an insecticide application.” Swezey and Larry Eddings, president of Pacific Gold Farms, speculated that by concentrating the pests in one place, an effective trap crop could be managed with bug vacs, thus eliminating the need for growers to run vacuum units across their entire strawberry plantings. If effective, the approach would not only decrease WTPB damage to the strawberry crop, but would save time and energy by cutting down on the area that needed to be vacuumed, and would conserve populations of beneficial insects in the crops. In 2002 and 2003 the Center research team of Swezey and research assistants Janet Bryer and Diego Nieto worked with Eddings and his staff at a Pacific Gold Farms site in Prunedale to test their theory. Grants from the Organic Farming Research Foundation and the US Department of Agriculture’s Western Sustainable Agriculture Research and Education program supported the work.Using a hand-held suction device, Bryer and Nieto collected insect samples in the trap crop plantings weekly beginning in January 2003.
The samples were then frozen and insects were identified and counted under a dissecting microscope. They also monitored insects in row 1 of the strawberry plantings using the same technique. The radish trap crop flowered from February through the end of May, when it was removed. The alfalfa trap crop began flowering in mid April and continued to flower through September. On April 11,strawberry gutter system collaborators from Pacific Gold Farm began vacuuming the beds and trap crops with a tractor-mounted unit that includes three rectangular vacuum collectors that generate a suction of approximately 28 miles/hour . Operators drove the tractor at 1.2 miles per hour when vacuuming the rows, passing over the strawberry canopy at canopy height once a week, and over the alfalfa trap crop row two days a week each week through the season . In mid April, in addition to monitoring the trap crops, Bryer and Nieto began monitoring insects in strawberry rows 1, 2, 4, 8, and 16. They also examined berries from four randomly selected clusters of four strawberry plants ; each week, developing berries that showed signs of distinct WTPB damage were counted and removed, while undamaged berries were counted once they matured. Adult WTPB were first found in the radish trap crop vegetation on January 7, and in the alfalfa trap crop in mid April, when it began to flower. Based on a heat unit accumulation model1 initiated when the first adult was found on January 7, the researchers predicted that a second-generation adult would not mature until July 19 at the earliest; therefore, the WTPB adults found any time before this date had migrated to the crop . This result suggests that there is a six-month period during which migrant WTPB adults are attracted to trap crop vegetation at the edge of strawberry fields.
Figure 1 shows total accumulation of WTPB in the unvacuumed trap crop treatments and the adjacent row of strawberries. Significantly more WTPB were found in the alfalfa than in either the radish trap crop or row 1 of strawberries. For seven weeks in April and May, when both the radish and alfalfa trap crops attracted adult WTPB or nymphs hatched in the vegetation, and when the grower was conducting commercial field vacuuming treatments, alfalfa attracted or retained over 7 times more WTPB than the radish trap crop. Although it flowers and matures somewhat later in the spring, alfalfa was a significantly more effective trap crop for WTPB. This result has management implications for central coast growers. “We’d experimented with a variety of trap crops through the years, including radish, mustard, alyssum, and other flowering annuals and perennials,” says Swezey. “But we’ve found that the radish and some of the other crops can become difficult to deal with once they begin to die back in the summer. Given the results of this study, which show that alfalfa is far more effective at attracting WTPB, we are focusing on alfalfa.” Because heavy spring rains often continue through April, tractor-mounted vacuum management of a trap crop can only begin in early May, when muddy conditions have diminished. This is an optimum time to begin alfalfa trap crop vacuuming. Pattern of WTPB Numbers and Strawberry Damage by Treatment and Row In June, weekly, tractor-mounted vacuuming of the alfalfa trap crop reduced total WTPB by 70% compared to the unvacuumed trap crop . The vacuumed trap crop treatment had the same accumulated WTPB as either the whole-field vacuuming treatment or the untreated control. In contrast, the unvacuumed trap crop consistently accumulated higher numbers of WTPB in strawberry rows 1, 2, 4, and 8. There were no differences among treatments at row 16, indicating that the trap crop’s effect on WTPB numbers ended somewhere between rows 8 and 16. Why the total WTPB numbers in the untreated control were consistently low in June is not clear. It’s possible that whole-field vacuuming in the commercial fields surrounding this experiment lowered the general level of WTPB in the small test plots. Movement or “sinking” of WTPB to nearby trap crops could also explain the low numbers in the control plots.
As shown in figure 3 , the vacuumed trap crop treatment had a significantly lower percentage of damaged strawberries than either the whole field vacuuming or the untreated control . Blueberries offer small-scale growers a potentially profitable “niche” crop that can be developed as a U-pick operation or incorporated into other marketing activities. Although the plants need several years to get established and require careful soil preparation and fertility management, a successful blueberry crop can generate $30,000 to $50,000 per acre . To learn more about the best-performing varietal options for organic growers on California’s central coast, the Center initiated a variety trial of mostly low-chill, high bush blueberries at the UCSC Farm in the fall of 2003. This project is being conducted in collaboration with Aziz Baameur, Small Farm Program Advisor for Santa Clara County’s UC Cooperative Extension office, and Mark Bolda, UCCE’s central coast Strawberry and Caneberry Advisor. Blueberries need well-drained, acidic soil in order to thrive. In November 2003, UCSC Farm manager Jim Leap applied sulfur to the trial site at a rate of approximately 2,000 pounds per acre as well as 3–4 inches of acidic mulch, then created raised beds for the plants. With the help of second-year apprentices Aaron Blyth, Carissa Chiniaeff, Allegra Foley, Estrella Phegan, Ratoya Pilgrim, and Matthew Sutton, the research team planted out 17 varieties of blueberries in January 2004. The trial includes 4 replicates of each variety planted on 3-foot plant in-row spacing with 5 feet between rows. Peat was applied in the planting hole to further lower the pH. Varieties being tested are: Biloxi, Bluecrop, Duke, Emerald, Jewel, Jubilee, Misty, Oneal, Ozarkblue, Millennia, Santa Fe, Sapphire, Sharpblue, Southern Belle, Southmoon, Star, and Windsor. After planting, the beds were mulched with several more inches of acidic bark, and drip tape was laid on top of the mulch. Plants are irrigated weekly with the drip tape, and during each irrigation vinegar is injected into the irrigation water to maintain a low pH. Phytamin, a liquid nitrogen fertilizer, is being applied through the drip lines monthly during the summer to maintain adequate nitrogen levels and get the plants off to a strong start. Over the next several years, the research group will evaluate a variety of factors,grow strawberry in containers including overall plant vigor, disease and pest resistance, and eventually, harvest dates, fruit taste and quality, and fruit production. Although the first harvest is still 12 to 18 months away, Leap is excited about the trial. “Blueberries offer a great marketing opportunity for small scale organic growers,” he says, adding that, “this project has also created great opportunities for interactions between the Center and our local UCCE advisors.” A blueberry field day organized by the Center, UCCE, and the Community Alliance with Family Farmers was held in early June, bringing farmers and gardeners to the UCSC Farm for a look at the new plantings. Speakers included Baameur, Leap, and Bolda, as well as UCCE researchers Richard Smith, who discussed organic weed management, and Laura Tourte, who talked about blueberry economics and marketing.As an environmental scientist, Center faculty affiliate Deborah Letourneau believes policy decisions should be based on the best information available at the time. That’s why she’s trying to fill an information gap with her latest research on genetically modified plants.
As insect-resistance is bred into major crops, Letourneau wonders how those crops’ wild relatives might be affected if they pick up the new traits. “There’s been a lot of research on crop-to-crop movement,” said Letourneau, referring to the contamination of organic corn grown adjacent to genetically modified corn. “But we don’t know that much about the biology of wild crop relatives. If genes transferred, would it make them more weedy, more hardy, more invasive?” To address these questions, Letourneau, a professor of environmental studies at UCSC, along with doctoral candidate Joy Hagen and Ingrid Parker, an associate professor of biology, have begun a three-year study to see what the consequences would be if GM genes transferred from Brassica plants through cross-pollination to their wild relatives. Plants in the Brassica, or cole, family include many vegetable crops, such as broccoli, Brussels sprouts, cabbage, cauliflower, and kohlrabi, as well as common weeds like wild radish and wild mustard. “Weed problems translate into economic problems for farmers,” said Letourneau, noting that 75 percent of cole crop production in the United States is concentrated on the Central Coast of California. Stubborn weeds require more herbicide applications, with accompanying higher labor costs and environmental impacts, she said, adding that highly invasive weeds can threaten native species on non-agricultural lands, too. Letourneau is a leading authority on the genetic modi- fication of plants. A member of the National Academy of Sciences’ 12-member panel investigating the environmental consequences of GM plants, she also coedited the 2002 book, Genetically Engineered Organisms: Assessing Environmental and Human Health Effects. Parker’s background is in applying mathematical models to ecological risk assessment for GM crops. More than 25 percent of corn grown in the United States has been genetically engineered to contain the toxin of the Bacillus thuringiensis soil bacterium, which disrupts the digestive system of a caterpillar. Transgenic cotton and potatoes also produce Bt toxin. Little is known about the role Bt-susceptible herbivores, including caterpillars, play in regulating the health and spread of wild crop relatives. In their research project, Letourneau and Hagen are protecting wild relatives from caterpillar damage to see what could happen if modified genes moved from Brassica crops to their wild relatives. The simulation is necessary because the research is being conducted in open fields—not inside greenhouses—where risks of contamination by GM plants would be high, said Letourneau. To mimic an effect of gene transfer, the UCSC researchers are spraying Bt on wild radish and wild mustard growing adjacent to commercial cole crops, and they will use models to evaluate the subsequent fitness, weediness, and invasiveness of the weedy relatives, said Letourneau. “We can’t use real transgenic crops, but we wanted to conduct this work where wild relatives live side-by-side with commercial crops,” said Letourneau. Research sites include the Center’s on-campus Farm and agricultural parcels adjacent to natural ecosystems from Wilder State Park to Elkhorn Slough Reserve. Genetic links between crops and weeds are remarkably common, and cole crops are no exception, noted Parker. “In the past, the evolution of many weeds has been driven by genes coming from crops,” she said. “Now those genes will be specially engineered by humans.” Research on consequences for wild relatives is overdue, said Letourneau, noting that field-testing of GM cole crops for California has been under way since 1999. “This kind of research is important now, during the process of risk assessment, to know whether new modified crops should be deregulated or not,” she said. “There are a lot of Bt crops in the pipeline.