- Vegetables: broccoli, cabbages, cauliflower, brussel sprouts
- Education and Training: demonstration, extension, networking, on-farm/ranch research
- Farm Business Management: whole farm planning
- Natural Resources/Environment: biodiversity, hedges - grass, habitat enhancement, hedgerows, wildlife, hedges - woody
- Pest Management: biological control, field monitoring/scouting, integrated pest management
- Production Systems: agroecosystems, holistic management
- Sustainable Communities: sustainability measures
My graduate research investigates the potential for natural habitat to provide pest control services to nearby farmland. This research addresses the Western SARE Region goals of: 1) promoting good stewardship of natural habitat, and 2) reducing the use of toxic materials in agricultural production. The first goal, promoting good stewardship of natural habitat, can be achieved by ascribing an economic value of natural habitat on a per-area basis, to aid in cost-benefit analysis involved with land-use decisions. By explicitly testing how well natural enemies contain pest populations and pest damage in landscapes with different proportions of natural habitat, I will be able to quantify the pest control service provided by natural habitat near farms and calculate the economic savings provided by a given level of pest control. The second goal, reducing the use of toxic materials in agricultural production, can be reached through a better understanding of the factors affecting the provision of natural pest control. Pesticides present a serious risk to the health and safety of those involved in agriculture. Enhancing communities of natural enemies of agricultural pests could curb our dependency on these chemicals while providing a much more sustainable means of pest control.
Project objectives from proposal:
My research will determine whether and to what degree natural habitat provides pest control services to nearby farmland. I am also concerned with the interaction between the landscape and the local scale, and will investigate how landscape structure across scales affects natural enemy communities and the pest control services they provide on farm sites. My objective is to quantify the amount and/or type of natural habitat necessary for a given level of pest control service, in order to enable economic valuations of this service. This coincides with SARE’s national and regional goal of enhancing and promoting good stewardship of the natural resource base upon which the agricultural economy depends; my research will enable cost-benefit analyses of land use in agricultural areas, helping to better quantify the value of natural habitat. My research also addresses the Western Region’s goal of protecting the health and safety of those involved in food and farm systems by reducing the use of toxic materials in agricultural production, since establishing a sustainable and natural means of pest control will help to reduce our dependency on pesticides.
My research will focus on broccoli, cauliflower and cabbage, the most important cole crops in the U.S., collectively comprising a $1.2 billion-per-year industry. Aphids are a major pest of cole crops and can be controlled by natural enemies if not disrupted by pesticides. Important natural enemies of aphids include lady beetles, lacewings and syrphid fly larvae. The broader landscape surrounding the farm is likely to play a major role in determining distributions of these extremely mobile natural enemies. Syrphid flies are especially vulnerable to pesticides and must migrate into the fields from surrounding areas.
The study will be based in Central California, on 25 vegetable farms in Santa Cruz and Monterey counties, which have already been contacted and have given permission. The 25 farms were chosen to represent a gradient of landscapes, ranging from less than 10% to more than 80% natural habitat within a 1.5 km radius of the farm (the area explaining the most variation in natural enemy populations over a changing landscape). These landscapes vary not only in the total amount of natural habitat, but in the types and variety of natural habitat present. This will provide the opportunity to examine effects of natural habitat more closely, addressing what factors of natural habitat are most important (amount, composition or heterogeneity). Additionally, 19 of the 25 farms use habitat modifications such as hedgerows to encourage beneficial insect populations, and this subset is fairly uniformly distributed across the landscape gradient. This will enable me to look at possible interactions between small-scale variables such as hedgerows and larger-scale differences in the natural habitat in the broader landscape.
In the first year of the study, I will use vacuum and sweep-net sampling to collect aphids and their predators (lady beetles, lacewings and syrphid flies) in broccoli, cauliflower and cabbage fields once a month at each of the 25 farms during the summer growing season. Whichever crop type exhibits the most variation in natural enemy abundance and diversity across the landscape gradient will be the focal crop for the second year of my study. In this first summer, I will also be performing pilot studies for the experimental exclosures in the second year of the study.
In the second year of the study, I will use experimental exclosures to test whether natural enemies better contain pest populations and prevent a greater amount of crop damage from pests on farms in landscapes with more natural habitat. The experimental treatment will involve placing wire cages on 10 plants per field (in one field per farm for a total of 250 cages) to exclude flying natural enemies, using a mesh size of 8 mm to minimize changes in microclimate and covering the cage in a sticky glue to capture insects that could fit through the mesh. Control cages, lacking mesh on the sides to freely admit natural enemies, will be paired with each experimental cage (another 250 cages). Temperature and relative humidity will be monitored in both control and experimental cages to detect any appreciable microclimate differences. I will be determining optimal cage design, initial aphid density and experimental duraction during the pilot studies in the first summer.
Aphids will be counted through visual inspection of each of the 500 plants prior to installation of the cages and after their removal. Any natural enemies detected during the initial inspection will be removed from the experimental treatments, and any natural enemies present at the end of the experiment will be recorded in all treatments. All 500 plants will be harvested at the end of the experiment to assess biomass. Thus, I will be able to determine differences in aphid densities and estimate yield loss in the presence and absence of natural enemies across the gradient of landscapes in my study.
My statistical methods will employ regressions to examine the relationship between the proportion of natural habitat in the landscape and two factors of pest control: pest containment, as defined by the difference in aphid densities with and without natural enemies, and crop damage, as estimated through the difference in biomass or percent herbivory with and without natural enemies. Multivariate regressions can incorporate additional landscape variables, including the presence or amount of small-scale habitat modifications such as hedgerows and the composition or heterogeneity of the natural habitat present in the landscape.
By testing how well natural enemies contain pest populations and pest damage in landscapes with different proportions or types of natural habitat, I will be able to determine the amount of pest control service provided by natural habitat near farms. The next step will be to calculate the economic savings that a given level of pest control service provides. This can be quantified by scaling up from the yield loss prevented by natural enemies determined by my experiments at the plant level, to estimate yield loss prevented at the farm level and multiplying by the value of the crop. Economic valuation of natural habitat will help direct restoration and conservation efforts, whether applied at the regional level by federal or state government, or at the local level by individual farmers. My analysis on the interaction between smaller-scale habitat modifications and large-scale landscape variables will be especially useful to inform farmers of the IPM strategies best suited to their landscape.
I will use several outlets to disseminate my findings to producers. The farmers on whose farms my study is based present the first opportunity to share my results; I will summarize my findings in a newsletter format to them and let them know where they can expect to see my research published. I will attend and hope to present at the Eco-Farm Conference in Santa Cruz, a workshop organized by the Ecological Farming Association, which will provide me with the opportunity to network with local farmers. I also intend to publish through the University of California’s Sustainable Agriculture Research and Education Program that works directly with farmers to keep them informed of recent research that could benefit them. My research will also contribute to the Community Alliance with Family Farmers’ program on Farmscaping for Wildlife and Conservation and to their publications that they distribute to farmers. Finally, I plan to plug into the USDA’s Natural Resources Conservation Service, which provides an enormous amount of outreach to farmers and creates conservation programs to benefit farmers.