A Multidisciplinary Approach to Evaluate and Aid the Transition From Conventional to Low Input Pest Management Systems in Stone Fruits

Kent M. Daane

Co-authors: R. S. Johnson, Dept. of Pomology, University of California, Davis; T. J. Michailides, Dept. of Plant Pathology, University of California, Davis

A keystone in any sustainable system is the reduction or elimination of fuel inputs for crop and pest. Further, development of sustainable systems should consider the interactions between different management practices, using a "whole farm" approach. Unfortunately, researchers often work on crop and pest management systems as separate issues. Here, we present results from research/extension activities in stone fruit that sought to combine individual studies in crop management with least-toxic controls for key orchard pests. This work also details the extension of research developed on small farms and experimental blocks to the larger farming community.

Crop management studies began in an experimental block at the University of California’s Kearney Agricultural Center (KAC), located in San Joaquin Valley. Soil fertility is the building block of sustainable systems and, in stone fruits, fuel inputs begin with chemical fertilizers. Nitrogen (N) is the main nutrient supplied by fertilizers and is needed to stimulate growth of fruiting shoots for high productivity and large fruit size. While most stone fruit growers apply ~160 lbs N/ac/yr, it is not uncommon for individuals to apply up to 300 lbs N/ac/yr, believing this practice can increase crop yields. Aspects of N fertilization on crop management were studied in an experimental 'Fantasia' nectarine block at KAC. The five fertilization treatments (RBD, 3 replicates) tested were: an unfertilized control and 100, 175, 250, and 325 lbs N/ac/yr (initiated in 1983). Results showed that good productivity and fruit quality can be maintained at moderately low N rates, which can probably be supplied by leguminous cover crops.

During this same period, separate studies were being conducted to develop least toxic pest controls – often working with on small farms with innovative growers. One of us (TJM) observed a natural resistance to infections by brown rot, Monilina fructicola, of nectarine fruits collected from underfertilized trees. Similarly, studies of arthropod pests found low or high fruit damage from oriental fruit moth (OFM), Grapholita molesta, and peach twig borer (PTB), Anarsia lineatella, had less connection to natural enemy levels than to plant vigor – also linked to N fertilization.

These observations were put to test in the KAC fertilization block, where N treatments had been maintained for eight years. Results showed the 100 lbs N/ac/yr rate resulted produced sufficient vegetative growth to maintain yields and fruit weights equivalent to higher fertilization rates. Further, higher N fertilization reduced fruit red color, increase the possibility of leaching nitrates into the ground water, and had no affect on most of postharvest parameters measured. For pest management, N fertilization was positively correlated to increased levels of brown rot blossom infection, the symptomless infections of green fruit (latent infections), and the susceptibility of mature fruit to brown rot. Increased N resulted in a greater number of fruit dropped and decayed by brown rot and in more mummified fruit hanging on the trees. Similarly, N fertilization was correlated with greater OFM and PTB fruit infestation. Higher pest densities were attributed to changes in the number of host sites (growing shoots), especially post-harvest when increased pest densities represents an increase in the overwintering pest population and potential damage to next season's crop.

Using lowered N fertilization as a foundation for sustainable management, we sought to demonstrate least-toxic farming practices on conventional farms. This Western Regional SARE project used a grower-collaborative approach to make management decisions and was supported by a multidisciplinary research team. Least-toxic pest controls were used whenever possible. For example, on these conventional farms, moth pests were controlled with a dormant application of oil and an organophosphate (for PTB) combined with one or more summer application(s) of an organophosphate or carbamate (for PTB and OFM). This was replaced by least-toxic pest controls (e.g., Bacillus thuringiensis and pheromone confusion) combined with lowered N fertilization levels and cover cropping to manipulate beneficial insects. The successes and failures of this three-year project are discussed (only one of three farms adopted sustainable practices). Results suggest that least-toxic pest controls are economically feasible for large commercial operations. However, adoption of these practices remains a personal decision, often founded on past experiences or beliefs rather than scientific evidence. Therefore, to compete the extension of developed sustainable stone fruit practices, a demonstration block, the "Orchard Odyssey," was established at KAC. Since 1996, this block has been visited by >2,000 elementary to high school age students, with educational outreach designed to highlight alternative farm practices to these potential future farmers.

Kent M. Daane
Research Entomologist
Division of Insect Biology
Department of Environmental Science, Policy and Management
University of California, Berkeley
9240 South Riverbend Ave.
Parlier, CA 93648
Tel: (209) 646-6522
Daane@uckac.edu

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