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Open Access Publications from the University of California

Volume 71, Issue 1, 2017


Issue cover
Cover Caption: Complete contents, including news and opinion featuresDrone-mounted cameras and sensors promise more and better data to guide the management of working landscapes and natural areas. Here, a DJI Inspire 1 drone flies over the UC Berkeley Blue Oak Ranch Reserve in Santa Clara County during a training for managers from across the UC natural reserve system. Photo by Evett Kilmartin.

Research and Review Articles

The palm weevil Rhynchophorus vulneratus is eradicated from Laguna Beach

In October 2010, Rhynchophorus vulneratus, originally identified as the red palm weevil, R. ferrugineus, was discovered infesting Canary Island date palms in Laguna Beach, California. The red palm weevil has caused extensive mortality of palms in the Mediterranean, the Middle East and North Africa, and its discovery in California caused concern for the state's ornamental palm and date industries and the many palms in Southern California landscapes. A rapid, coordinated effort led to the deployment of traps baited with the weevil's aggregation pheromone, coordinated pesticide applications to privately owned palms and destruction of palms at advanced stages of infestation. Research confirmed the chemical components of the aggregation pheromone, assessed the efficacy of trapping strategies and resolved the taxonomic identity, native range and putative region of origin for the population detected in Laguna Beach. The last confirmed detection of a live R. vulneratus was Jan. 20, 2012. USDA-APHIS declared this weevil eradicated from California on Jan. 20, 2015. The estimated cost of the eradication was $1,003,646.

How many workers are employed in California agriculture?

In 2014, the average employment of hired workers in California crop and livestock agriculture, counting all occupations, rose by 10% to 410,900. However, although the state reports the number of jobs on farms regularly, it does not report the number of workers who fill these jobs. We analyzed all Social Security numbers reported by farm employers in 2014 and found two workers for each average or year-round equivalent farm job, making the total number of farmworkers employed in agriculture 829,300, or twice average employment. Approximately 83% of farmworkers had their maximum earnings with an agricultural employer in 2014, and almost 80% of those primary farmworkers were employed by crop support firms (392,000) or fruit and nut farms (154,000). Over 60% of all workers had only one farm employer, followed by 27% with two or more farm employers, and 35% were employed in Kern (116,000), Fresno (96,000) and Monterey (82,000) counties. These data show that California has a remarkably stable farm workforce: most farmworkers are attached to one farm employer, often a labor contractor who moves them from farm to farm.

Irrigation method does not affect wild bee pollinators of hybrid sunflower

Irrigation method has the potential to directly or indirectly influence populations of wild bee crop pollinators nesting and foraging in irrigated crop fields. The majority of wild bee species nest in the ground, and their nests may be susceptible to flooding. In addition, their pollination of crops can be influenced by nectar quality and quantity, which are related to water availability. To determine whether different irrigation methods affect crop pollinators, we compared the number of ground-nesting bees nesting and foraging in drip- and furrow-irrigated hybrid sunflower fields in the Sacramento Valley. We found that irrigation method did not impact wild bee nesting rates or foraging bee abundance or bee species richness. These findings suggest that changing from furrow irrigation to drip irrigation to conserve water likely will not alter hybrid sunflower crop pollination.

Wood chip denitrification bioreactors can reduce nitrate in tile drainage

Widespread contamination of surface water with nitrate-nitrogen (NO3-N) has led to increasing regulatory pressure to minimize NO3-N release from agricultural operations. We evaluated the use of wood chip denitrification bioreactors to remove NO3-N from tile drain effluent on two vegetable farms in Monterey County. Across several years of operation, denitrification in the bioreactors reduced NO3-N concentration by an average of 8 to 10 milligrams per liter (mg L-1) per day during the summer and approximately 5 mg L-1 per day in winter. However, due to the high NO3-N concentration in the tile drainage (60 to 190 mg L-1), water discharged from the bioreactors still contained NO3-N far above the regulatory target of < 10 mg L-1. Carbon enrichment (applying soluble carbon to stimulate denitrifying bacteria) using methanol as the carbon source substantially increased denitrification, both in laboratory experiments and in the on-farm bioreactors. Using a carbon enrichment system in which methanol was proportionally injected based on tile drainage NO3-N concentration allowed nearly complete NO3-N removal with minimal adverse environmental effects.