UC Organic Farming Research Workgroup Directory

Integrated Organic Cropping Systems
cover crop seeding rate and varietal effects on subsequent vegetable crop production

Organic Pest Management
weed management

Overview of Research Activities Underway and Future Directions

My research focuses on organic production systems. The objectives of my position are to conduct research on:

1. Organic nitrogen sources.

2. Efficient means of increasing soil organic matter.

3. Crop rotational schemes.

4. Cover cropping.

5. The effects of crop rotation, cover cropping, and compost treatments on soil organic matter build-up, soil quality, fertility and tilth, nitrogen leaching, water use efficiency, pest and disease incidence, and yield and quality of the harvested product.

6. Economic analysis of these treatments

I have been on the job since June 2001 and am in the process of developing a research program, however, currently I am focusing on the effects of cover crops on weed management. Weed management is the major research priority of organic farmers in the United States (Organic Farming Research Foundation, 3rd Biennial National Organic Farmers’ Survey, 1999). In terms of weed management, it appears that the cover crop is the weakest link in many organic farmers’ crop rotation and that substantial deposits are being made to the weed seed bank during cover cropping. I am interested in quantifying weed dynamics during cover cropping and developing cover cropping practices that reduce rather than contribute to the weed seed bank. I have started a few on-farm and on-station collaborative research projects that look at the effects of different cover crops, cover crop planting density and planting configuration on cover crop biomass production and weed seed production during cover cropping.

Overview of Research Activities in Previous positions

My Ph.D. research at UC Davis (Plant Biology) focused on understanding how plant resistance to insects changes as plants develop from the juvenile to adult phase of growth. I used the interactions between Eucalyptus globulus and 3 species of Australian psyllids (jumping plant lice) as a model system for this work. This work provides some of the first evidence that plant resistance to insects changes with plant development, and with this system showed that changes in resistance are due to anatomical differences between juvenile and adult phase leaves. The research involved field studies of insect behavior and plant histology, and is described in my most recent publications

My. M.S. research at Cornell University focused vegetative and seed production of Leucaena. Leucaena species are important trees in tropical agroforestry systems and provide small scale farmers with green manure, timber, fuelwood and fodder.

I developed new grafting techniques, tested rootstock effects and evaluated the feasibility of producing interspecific F1 hybrid seed in open-pollinated seed orchards in Hawai’i. The results are described in my publications from 1998.

Publications from Previous Research (Copies available on request. Electronic copies may be available in a few months when the USDA Salinas Web page is working).

Brennan, E.B. and R. Smith. (2003). Cover crop cultivar and planting density impacts on cover crop productivity, and weed biomass and seed production in an organic system in the Central Coast of California. In Proceedings of the California of Chapter of the American Society of Agronomy. pp. 80-88. California Plant and Soil Conference, February, 2003. Modesto, California.

Brennan, E.B., G.F. Hrusa, S.A.Weinbaum, and W.Levison Jr. (In Press). Resistance of Eucalyptus species to Glycaspis brimblecombei (Homoptera: Psyllidae) in northern California.

Brennan, E.B. S.A. Weinbaum, J.A. Rosenheim, and R. Karban. (In Press). Heteroblasty in Eucalyptus affects herbivory by psyllids. Environmental Entomology.

Brennan, E. B. and S.A. Weinbaum. 2001. Stylet penetration and survival of 3 psyllid species on adult leaves and ‘waxy’ and ‘de-waxed’ juvenile leaves of Eucalyptus globulus. Entomologia Experimentalis et Applicata 100:355-363.

Brennan, E.B. and S.A. Weinbaum. 2001. Performance of psyllids on juvenile and adult leaves of Eucalyptus globulus. Entomologia Experimentalis et Applicata 100:179-185.

Brennan, E.B. and S.A. Weinbaum. 2001. The Effect of Epicuticular Wax on Adhesion of Psyllids to Glaucous Juvenile and Glossy Adult Leaves of Eucalyptus globulus Labill. Australian Journal of Entomolgy 40:270-277.

Brennan, E.B. and S.A. Weinbaum. 2001. Psyllid responses to colored sticky traps and the colors of juvenile and adult leaves of the heteroblastic host-plant Eucalyptus globulus. Environmental Entomology 30:365-370.

Brennan, E.B., S.A. Weinbaum, and K.Pinney. 2001. A New Technique for Studying the Stylet Tracks of Homopteran Insects in Hand-Sectioned Plant Tissue Under Light or Epifluorescence Microscopy. Biotechnic and Histochemistry.

Thao, M.L., M.A. Clark, L. Baumann, E.B. Brennan, N.A. Moran and P. Baumann (2000). Secondary endosymbionts of psyllids have been acquired multiple times. Current Microbiology 41:300-304.

Thao, M.L., N.A. Moran, P. Abbot, E.B. Brennan, D.H. Burckhardt, P. Baumann. (2000). Cospeciation of psyllids and their prokaryotic endosymbionts. Applied and Environmental Microbiology 66:2898-2905.

Brennan, E.B., R.J. Gill, G.F. Hrusa and S.A.Weinbaum. (1999). First record of Glycaspis brimblecombei (Moore) (Homoptera: Psyllidae) in North America: Initial observations and predator associations of a potentially serious new pest of Eucalyptus in California. Pan-Pacific Entomologist 75:55-57.

Brennan, E.B., Mudge, K.W., and A. Sherrer. (1998). Open-pollinated interspecific F1 hybrid seed orchards of Leucaena. I. Rootstock effects. Agroforestry Systems 41:221-235.

Brennan, E.B., Mudge, K.W., and C. Elevitch. (1998). Open-pollinated interspecific F1 hybrid seed orchards of Leucaena. II Analysis of seedlings. Agroforestry Systems 41:237-250.

Brennan, E.B. and K.W. Mudge. (1998). Clonal propagation of Leucaena by single bud splice grafting with a new grafting tool, and by modified crown grafting. New Forests 15: 283-297.

Brennan, E.B. and K.W. Mudge. (1998). Vegetative propagation of Inga feuillei from shoot cuttings and air layering. New Forests 15:37-51.

Mudge, K.W. and E.B. Brennan. (1999) Asexual propagation of multipurpose and fruit trees used in agroforestry, pp. 157-190 in Agroforestry in Sustainable Agricultural Systems (L.E. Buck, J.P.Lassoie, and E.C.M. Fernandez, eds.). Advances in Agroecology. CRC Press, Boca Raton.

Brennan, E.B. (1993). Field performance of grafted seedless Leucaena. Nitrogen Fixing Tree Research Reports 11:81-83.

Brennan, E.B. (1992). A new grafting technique for Erythrina and Leucaena, and possibly other nitrogen fixing tree species. Nitrogen Fixing Tree Research Reports 10:85-88.

Brennan, E.B. (1990). Using farmers and their ideas for effective extension work, in Proceedings of Strategies and Methods for Orienting Multipurpose Tree System Research for Small Scale Farm Use (C. Haugen, L. Medema, C.B. Lantican, Eds.). Forestry/Fuelwood Research and Development Project (F/FRED), and International Development Research Centre of Canada. pp. 94-97.