Biologically Integrated Farming Systems for California Prunes: Dormant Organophosphates, Secondary Pests and Participants

Gary L. Obenauf

The California Prune Board (CPB) is a State Marketing Order that represents the 1,400 growers and 21 packers of California prunes. California produces approximately 200,000 dried tons annually on 81,000 bearing acres. California prune production is primarily in the Sacramento and San Joaquin Valleys. California represents 99% of the US total and about 70% of the world total. The annual crop value is approximately $200 million.

The prune grower has invested about $13,000 per acre before yields are sufficient to have a net return per acre, usually the eighth to tenth year. Prune orchards vary from 121 to 134 trees per acre and can be productive for 40 years. Approximately 50 acre-inches of water are applied annually, typically with flood irrigation systems. Weed control is accomplished with a combination of discing, mowing and herbicide use. Trees are pruned annually during the dormant season. Annual applications of 100 pounds of nitrogen per acre are common as well as frequent potassium applications. Harvest occurs from August through September. Prunes are harvested by shaking the fruit onto catching machines and then dried in dehydrators to 18 to 21 percent moisture.

A variety of insect, disease, nematode and weed pests attack California prunes. Severity of infestations varies from year to year and from area to area. The serious pests, peach twig borer (PTB), (Anarsia lineatella), leafrollers, brown rot, (Monlinia laxa and M. fructicola), and prune russet scab, (a physiological disorder), attack the fruit directly. Others, such as San Jose scale, Armillaria Root Rot, (Armillaria mellea), Phytophthora Root, Bacterial Canker and Crown rot (Phythphthora Spp.) can kill fruitwood, limbs and trees, thus greatly reducing yields. These pests require control measures to be taken at low population levels to prevent economic losses. However, other pests such as prune rust, mites, aphids, nematodes and weeds are indirect pests. Although they do not feed on the fruit directly, they cause damage by lowering yields and fruit quality i.e. lower sugars, smaller size, end and side cracks, premature drop, less fruit set, etc. It is possible to tolerate higher populations of indirect pests than of direct pests.

The Biologically Integrated Farming Systems (BIFS) Project is funded by the University of California Sustainable Agriculture Research and Education Program (UC/SAREP) administering matching funds from the State of California and the US EPA. IPFP serves as an umbrella program for several projects relating to reduced-risk of pesticides in prune production, including the BIFS Project. This project adds to the existing and past CalEPA/DPR projects and grants from UC/SAREP, USDA/CSREES and USDA/NRCS to the California Prune Board (CPB) and projects supported by CPB.

IPFP objectives are: 1) Develop and implement replacement pest management systems impacted by FQPA, 2) Reduce surface water contamination by organophosphates (OPs), 3) Reduce groundwater contamination, 4) Evaluate ground covers and cover crops for their ability to increase biological control of pest organisms and reduce groundwater contamination by toxic pesticides, 5) Optimize nitrogen and other nutrient programs, 6) Optimize water use, 7) Reduce human exposure to pesticides, 8) Reduce risks to urban environments, 9) Delay the development of insect, disease and weed resistance to currently used pesticides.

The prune project is targeting a 90 percent reduction of OPs in the dormant season over the next 5-7 years. Additionally, when an in-season treatment is needed, softer pesticides are used when possible. Additional monitoring costs will, in most cases, be offset by reduced use of pesticides per season. A potential obstacle will be to address the shift of a relatively minor pest, aphids, when using dormant OP applications to a significant pest when OPs are not applied as a dormant spray. During the 1999 season, 8 of the 22 IPFP sites had significant populations of aphids.

We currently have 22 grower demonstration/research sites. Each site has three plots: conventional practices or grower’s pest control program, reduced risk pesticide use and untreated control. These 22 orchards require 708 acres of prunes. The 22 prune growers farm better than 6,000 acres of prunes.

A Management Team was established in June 1998 and is composed of prune industry representatives (prune growers, prune processors, and California Prune Board), University of California personnel (Farm Advisors and Experiment Station), PCAs, environmentalists, and members of the regulatory community. The Management Team provides the direction and makes adjustments in the project as things progress. Approximately 10 field scouts monitored each plot weekly during the growing season using the 10 monitoring protocols developed for the project.

A quarterly IPFP Newsletter goes to all prune growers in California. Meetings are held through the year to share with the industry what we are doing and encourage them to try it themselves. Our strongest advocates to date are the prune growers involved in the plots as they have significant influence on neighboring prune growers

Gary L. Obenauf
California Prune Board
144 W. Peace River Drive
Fresno, CA 93711-6953
Tel: (559) 447-2127
gobenauf@agrc.cnchost.com

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