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IPM on coastal lettuce adds 4 cents extra cost per carton

The three-year Central Coast Vegetable IPM Project showed use of “soft” insecticides instead of conventional chemicals on head lettuce costs four cents more per carton than standard production costs.

Bill Chaney, Monterey County farm advisor and coordinator of the project, recently told the California Lettuce Advisory Board meeting at Seaside that yields and quality were the same for both grower standard treatments and IPM.

Grower standard included all registered materials for the crop, and IPM excluded organophosphates, carbamates, and pyrethroids, wherever alternatives were available.

Although the project originally set out to craft strategies against the pea leafminer, problems with that pest declined and the lettuce aphid emerged as a major threat.

Realigned to deal with the new aphid pest, the project continued to explore the impact of a system that would exclude pesticides under scrutiny of the Food Quality Protection Act (FQPA).

While the trials demonstrated efficacy of softer products, they also revealed a continuing need for the standard chemistry to fill “holes” in pest control, Chaney said.

The series of commercial-scale field demonstrations during the 1998, 1999, and 2000 seasons were conducted with a broad collaboration between growers, pest control advisors, pesticide manufacturers, University of California Cooperative Extension, and the funding organization, the Pew Charitable Trust.

The project was carried out at 46 field demonstrations on 667 acres from Watsonville to Oxnard. “This acreage,” Chaney said, “represented a risked investment of $2 million, conservatively, by the grower cooperators, which does not include the great expense of staff time donated to cooperating in the project.”

Credits PCAs

Insect populations and damage were monitored by project staff and cooperating PCAs, but treatment decisions were made by the PCAs. Chaney credited PCAs involved with the project as being “aggressive in reducing the use of pesticides.”

Harvest data, along with yield and quality indicators, was gathered for each trial and pesticide costs and yield data were calculated for per-carton costs for each treatment.

Chaney told the lettuce board the reduction in number of IPM applications compared with applications of the three standard insecticide groups was 87 percent for head lettuce, 88 percent for romaine lettuce, and 72 percent for celery.

“However,” he said, “the project clearly shows that eliminating these FQPA-targeted materials is not possible at this time. One or more of the excluded pesticides was used on the IPM treatment for 38 percent of the head lettuce, 29 percent of the romaine, and 100 percent of the celery.”

Chaney also said harvest quality and quantity differed little between the two methods. Yields for romaine and celery were essentially the same between treatments, although in head lettuce, 12 percent of the field trials had significantly higher yields from the IPM treatments.

On the other hand, many of the newer and softer IPM materials are more expensive, contributing an average of four cents more to per-carton costs.

Acre, carton costs

Overall average costs for the 1998, 1999, and 2000 seasons were $308.80 per acre, or 40 cents per carton, for the standard treatment and $358.09 per acre, or 44 cents per carton, for the IPM treatment.

By-products of the IPM project are new photographs and identification materials to distinguish the lettuce aphid from other aphids.

“Lettuce aphid has been a hit-and-miss problem over the last three years. It's been bad but not as severe as we suspected it might be,” Chaney said.

Chemical control is difficult because lettuce aphids move deep into the lettuce heads, safe from sprays and free to reproduce profusely.

Syrphid fly larvae are an important biological control against lettuce aphid. Less than three of the predators can consume 80 aphids, but the trick to using them is timing for the critical lag between syrphid and aphid populations. When syrphid numbers catch up, the aphid numbers fall to zero, at which point the syrphids starve and fade out.

Since both contaminate produce, Chaney explained, the object is to key their presence about a week before harvest so both populations have crashed and are absent before picking crews go into the field.

(In another project funded by the lettuce board, USDA geneticists at Salinas are transferring, by classical breeding techniques, resistance to lettuce aphids from European types to western types. When placed on resistant European lettuce, the aphids fail to thrive and then disappear. The breeding process, intended for protection of both head and romaine lettuce, is expected to take several years before resistant material is available for commercial seed companies to develop new varieties.)

Chaney said he observed that after applying Success for aphid control more aphids were counted on treated portions than on untreated controls. That is because the material acted against syrphid predators.

Neonicotinoid-class products, including imidacloprid in its soil-applied Admire and foliar-applied Provado forms, are also under study as lettuce aphid controls. Chaney said Actara, Platinum, Assail, and others are similar and are in the process for registration.

Pea leafminer

He said data on the project's studies on pea leafminer, which revisited coastal lettuce fields in a late but robust fashion in 2001, are being processed for presentation a future lettuce board meeting.

“We've been looking at a variety of materials in the field, Agrimek, Trigard, and Success as a sort of standard, the neo-nicotinoids, neem products, and Pounce,” Chaney said, adding that he has observed signs of reduced leafminer susceptibility to older products.

USDA geneticists at Salinas are advancing toward plant resistance to pea leafminers in head, romaine, leaf, and butterhead lettuces.

e-mail: [email protected]

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