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Delta Fruit Farms Curb Pest Sprays
Picking that perfect pear or tarnish-free tomato at harvest time has historically required spraying pesticides - sprays that can end up in Bay- Delta soils and water and affect farmworker health. But some Delta growers are trying out new pest controls that bedevil bugs and blight while sparing the environment.
On Randall Island, UC Berkeley's Dr. Steve Welter has teamed five pear growers and five pest advisors in a three-year experimental project aimed at interrupting the breeding cycle of the destructive codling moth. The little moth gives big headaches to growers - a single moth infesting a single pear can affect all the pears surrounding it - in a market that only tolerates 2% damage to fruit. To control the moth, growers typically spray Guthion, a broad-spectrum organophosphate pesticide. But according to Welter, a "cluster of resistance" has evolved among Delta moths, which appear to have better biochemical mechanisms for detoxifying pesticides than moths in other areas. In other words, more Guthion has had less effect.
As an alternative, Welter and his five growers have been experimenting with sex pheromones, which females moths emit to attract males for breeding. Using twist-ties, the growers have attached pheromone-saturated plastic disks - around 400 per acre - to pear tree branches over 760 contiguous acres of orchards on the island, blanketing the orchards with pheromones.
"For the moths, it's kind of like being in junior high school," says Welter. "They can smell sex everywhere, but they don't know where to find it." The disoriented males can't find females, so in effect, the moths stop breeding, and the females lay unfertilized eggs.
The pheromone-using pear growers reduced Guthion use by an annual estimated average of 70% over the three-year project while keeping the infestation rate to just 7/10 of 1%. In a separate study, the cost of pheromone use was initially high, but equaled that of conventional pesticide treatment by the third year.
Welter found a "cascade" of accompanying positive benefits, including increasing control of other secondary pests and increasing natural populations of beneficial predators and parasites. And introducing and establishing exotic beneficial insects is more successful in orchards not uniformly treated with broadly toxic organophosphate insecticides, he says.
Welter expects the Delta moths' resistance to Guthion to diminish over time, meaning that the pesticide could be effectively used in small amounts to control border areas or heavy infestations, where pheromones are less successful. Welter says the experiment required a new cooperation-based approach for growers. "We're asking them to behave in a very different way - they have to share information about who has a problem where, and to what extent," he says. "The program won't work if you just hand out the ties."
Elsewhere in the Delta, five Campbell Soup tomato farmers are trying out a set of integrated pest management (IPM) techniques on over 2,500 acres as part of the company's statewide pesticide reduction program. According to Campbell's Bob Curtis, the company decided to aggressively market the program to growers in response to consumer and environmental concerns about pesticides.
Tomato growers can be involved in the program at any of three different levels. In the first, the company splits a field with a grower - the grower uses conventional pesticides and practices, while Campbell's demonstrates its IPM approach. "We pay for any losses incurred in the IPM-test portion of the field," says Curtis, "so it's a low-risk, low-heartburn situation." Curtis says this "foot-in-the-door approach" often evolves to the second level, where Campbell's and growers use cooperative monitoring of field conditions to further reduce pesticide use. At the third level, Campbell's and growers jointly fine tune monitoring techniques and conduct pest control research projects.
At all three levels, a sophisticated new statewide disease-forecasting model that employs daily monitoring information from in-field computers has proved effective, says Curtis. The computers record temperature and moisture conditions - leaf and fruit wetness - in fields representative of eight California microclimates, two of which are in the Delta. Scientists track these parameters in relation to the conditions required for tomato blackmold and other diseases to flourish.
"We found out the best time to spray is just before the disease takes off," says Curtis. "This model allows us to figure out exactly when to apply fungicides to protect the plant."
To expand its data collection and forecasting abilities for the California tomato industry, Campbell's is working with the state and the University of California to install regional networks that eventually could provide, for example, a daily area fungicide report that cues growers when it's time to spray. In the meantime, Campbell tomato growers statewide have dropped synthetic pesticide applications by 30%.
Whether to stop a moth from mating or a mold from germinating, these two projects clearly show that creative work with nature and high technology can do much to reduce growers' use of chemicals that all too easily run off their fields and into Estuary waterways.
Contact: Bob Curtis (916)395-5086; Dr. Steve Welter (510)642- 2355
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