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Open Access Publications from the University of California


California Agriculture is a quarterly peer-reviewed journal reporting research, reviews and news on California’s agricultural, natural and human resources.

Volume 70, Issue 3, 2016

The evolving berry industry

Issue cover
Cover Caption: Complete contents, including news and editorial featuresStrawberries in Santa Cruz County. The articles in this issue survey a range of issues in California’s evolving berry sector, including the economics of the industry’s growth (page 107), the impact on growers of new fumigation regulations (page 116), and new approaches to managing soilborne pathogens (pages 101, 104 and 137).

Research and Review Articles

The evolving fresh market berry industry in Santa Cruz and Monterey counties

The fresh market berry industry in Santa Cruz and Monterey counties has contributed significantly to the agricultural vibrancy of the two counties and the state of California. Dramatic growth in strawberry, raspberry and blackberry production has been documented over the last 50 years, and most notably since the 1980s. Factors influencing this growth include innovations in agricultural practices and heightened consumer demand. Here, we review the historical context for the berry industry in Santa Cruz and Monterey counties. Organic production, production economics and challenges for the future are also discussed.

Revised chloropicrin use requirements impact strawberry growers unequally

Buffer zone requirements are by nature spatial and their effects are site-specific, with some fields — because of their location — more impacted than others. Using a set of strawberry fields in Ventura County that were preplant soil fumigated in 2013 as a baseline, we examined how much acreage eligible for chloropicrin fumigation would have been lost if either of two buffer zone distance regulations had been in effect: any one of the four sets of alternative distances proposed in May 2013 by the California Department of Pesticide Regulation (DPR) or the buffer zone distances DPR released in January 2015. Buffer zone distances are based on several factors including the anticipated protection of human health, referred to as the percentile of protection. We find that the effects are highly dependent on the percentile of protection. From 4% to 29% of the fumigated blocks analyzed would have had an increase in buffer zone acreage depending on the percentile of protection. In those blocks, the share of total acreage that would no longer have been eligible for fumigation with chloropicrin varied from 3% to 45%. We also identify strategies that growers employed to reduce required buffer zone distances under use requirements in effect in 2013. The most frequently used strategies were using a tarp type with the lowest buffer zone requirements (“60% tarp”), extending a buffer onto a neighboring property, road and/or farm path, and reducing application rates. The results have an important policy implication: spatially defined use regulations have very different effects for different fields; aggregated industry-level analyses will miss the range of impacts on growers.

Strawberry growers wavered over methyl iodide, feared public backlash

Methyl iodide, once promoted as a suitable alternative to methyl bromide for soil fumigation in strawberry systems, was withdrawn from the market in 2012 after a contentious regulatory battle that revolved around its high toxicity. At the time of its withdrawal, Arysta LifeScience, the maker of the chemical, claimed that it was no longer economically viable. In this study, I investigated what made the chemical nonviable, with a specific focus on growers’ nonadoption of it. Interviews with strawberry growers in the four top California strawberry-growing counties revealed that growers’ decisions not to use it were primarily related to public disapproval, although the continued availability of methyl bromide and other fumigants played a contributing role by making adoption less urgent. The study results suggest that policies in place during the methyl bromide phaseout did not strongly encourage the development and extension of less toxic alternatives, which undermined the strawberry industry's position.

Fumigant dosages below maximum label rate control some soilborne pathogens

The activity of commercial soil fumigants on some key soilborne pathogens was assessed in sandy loam soil under controlled conditions. Seven soil fumigants that are registered in California or are being or have been considered for registration were used in this study: dimethyl disulfide (DMDS) mixed with chloropicrin (Pic) (79% DMDS and 21% Pic), Tri-Con (50% methyl bromide and 50% Pic), Midas Gold (33% methyl iodide [MI] and 67% Pic), Midas Bronze (50% MI and 50% Pic), Midas (MI, active ingredient [a.i.] 97.8%), Pic (a.i. 99% trichloronitromethane) and Pic-Clor 60 (57% Pic and 37% 1,3-dichloropropene [1–3,D]). Dose-response models were calculated for pathogen mortality after 24 hours of exposure to fumigants. Overall, the tested fumigants achieved good efficacy with dosages below the maximum label rate against the tested pathogens. In this study, Pythium ultimum and citrus nematode were sensitive to all the fumigants and Verticillium dahliae was resistant. For most fumigants, California regulations restrict application rates to less than the maximum (federal) label rate, meaning that it is possible that the fumigants may not control major plant pathogens. This research provides information on the effectiveness of these alternatives at these lower application rates. The results from this study will help growers optimize application rates for registered fumigants (such as Pic and 1,3-D) and will help accelerate the adoption of new fumigants (such as DMDS) if they are registered in California.

Managing for soil health can suppress pests

A “healthy” soil can be thought of as one that functions well, both agronomically and ecologically, and one in which soil biodiversity and crop management work in synergy to suppress pests and diseases. UC researchers have pioneered many ways of managing soil biology for pest management, including strategies such as soil solarization, steam treatment and anaerobic soil disinfestation, as well as improvements on traditional methods, such as reducing tillage, amending soil with organic materials, and cover cropping. As managing for soil health becomes more of an explicit focus due to restrictions on the use of soil fumigants, integrated soil health tests will be needed that are validated for use in California. Other research needs include breeding crops for disease resistance and pest suppressive microbial communities as well as knowledge of how beneficial organisms influence plant health.

Inconsistent food safety pressures complicate environmental conservation for California produce growers

Controlling human pathogens on fresh vegetables, fruits and nuts is imperative for California growers. A range of rules and guidelines have been developed since 2006, when a widespread outbreak of E. coliO157:H7 was linked to bagged spinach grown in California. Growers face pressure from industry and government sources to adopt specific control measures on their farms, resulting in a complex, shifting set of demands, some of which conflict with environmental stewardship. We surveyed 588 California produce growers about on-farm practices related to food safety and conservation. Nearly all respondents considered both food safety and environmental protection to be important responsibilities for their farms. Responses indicate that clearing vegetation to create buffers around cropped fields, removing vegetation from ditches and ponds, and using poison bait and wildlife fences are commonly used practices intended to reduce wildlife movements onto farm fields. The survey also revealed that on-farm practices vary substantially even among farms with similar characteristics. This variability suggests inconsistencies in food safety requirements, auditors’ interpretations or growers’ perception of the demands of their buyers. Although site-specific considerations are important and practices should be tailored to local conditions, our findings suggest growers, natural resources and food safety would benefit from clearer, more consistent requirements.

Soil testing for P and K has value in nutrient management for annual crops

Adequate nutrients in forms available to plant roots are essential for sustainable crop production. Soil testing for phosphorus and potassium availability allows growers and crop advisers to determine whether a soil is likely to respond to fertilization. As yields have risen with improved management and production systems, crop nutrient demand and the removal of nutrients with harvested crops have increased. An in-depth discussion of soil tests for phosphorus and potassium and their use in California cropping systems is clearly needed. We review how these nutrients become available to plant roots, how samples are taken and test results interpreted, complementary ways to assess the adequacy of supplies and what research is needed to improve soil testing for phosphorus and potassium.

Editorial, News, Letters and Science Briefs