SPATIAL EXTERNALITIES OF PEST CONTROL

Much work has already addressed optimal agricultural production strategies for individual farms. Less work has examined how individual farms affect and are affected by nearby farms. This project studies these externalities and examines how heterogeneity can improve or exacerbate these externality problems. Between 2000 and 2008, expenditures on pesticides increased by 37.6% in the U.S., and 2008 expenditures on pesticides were 5.8% of the countrys total expenditures on commercial agricultural inputs (USDA, 2009). Because pests are mobile, individual growers can impose externalities, positive or negative, on their neighbors. Identifying situations where these externalities exist can lead to more efficient pest control and a reduction of resources allocated to pest control. Some of the earliest forms of pest controls consisted of manipulating interactions between pests and beneficial organisms that predate or parasitize the pest. This manipulation is known as biological control, and the beneficial organisms, usually insects, are known as natural enemies of the pest (Hajek 2004). During the first half of the 20th century, the development of synthetic pesticides began. The use of these chemical controls can be very effective, but many kill natural enemies and other non-target organisms in addition to killing the pest (Smith and Kennedy 2002). The concept of integrated pest management (IPM) emerged in the 1960s. IPM considers the farm to be an agroecosystem and emphasizes the use of cultural and biological control feasible. IPM adoption rates vary across regions and crops, and chemical control is still the primary method of pest control for many growers (Smith and Kennedy 2002). Between 1992 and 2005, organic cropland more than quadrupled, driven by growth in demand (USDA, 2008). The rise in organic growers and growers making use of IPM results in agricultural regions containing both growers who would like to use beneficial insects and growers who use chemical controls that harm beneficial insects. Since beneficial insects move between fields, this juxtaposition of different pest management practices may yield spatial externalities. Chemical controls may impede growers efforts to rely on biological controls. Conversely, if biological controls are less effective, these controls may increase pest pressure felt by growers relying on chemical control. Variation also exists in the level of pest control effort. Some commercial citrus growers in California do not utilize any forms of pest control. These growers sell to packinghouses that price the fruit based on quality and send low quality fruit to processors. This system allows for a market for pest-damaged fruit and allows for the existence of inactive growers. In California and Florida, there exist homeowners with obackyardo citrus that is often not managed for pests as actively as citrus owned by most commercial growers. This lack of pest management may cause active commercial growers to face increased pest pressure. All of the externalities described above can lower a regions profits. Cooperative solutions would address these externalities and result in increased regional profits.

I model how socially optimal levels of pest control can deviate from Nash equilibrium levels when accounting for the movement of pests and predators or parasitoids of the pests. I apply this model to the case of organic and conventional neighbors and analyze how different management types exacerbate the spatial externalities found in homogeneous landscapes. I also model the effects of spatial externalities on the type of pest control chosen by the two types of growers. Some pesticides used by citrus and non-citrus growers kill predators and parasitoids of common citrus pests. In California, many citrus growers incorporate the use of beneficial insects. I test for externalities generated by the use of pesticides on citrus and non-citrus farms that are toxic to the beneficial insects utilized by these growers. I test for reductions in beneficial insect populations and increased reliance on chemical controls in areas with higher use of these toxic pesticides. I examine the externality generated by "hobby" commercial citrus growers in California. These growers have between 1 and 15 or so acres of citrus that largely go unmanaged. California climate allows for the production of citrus without substantial management. This fruit is generally of lower quality but can be sold to packinghouses or processors, receiving a lower price than higher quality fruit. Groves that are not managed likely harbor pests, and their close proximity to managed groves can lead to negative externalities. The results of this study will be directly applicable to Florida, where many homeowners have backyard citrus trees. The project will analyze spatial externalities arising from backyard citrus with respect to the Asian citrus psyllid in Florida. Current psyllid chemical controls are limited to broad-spectrum pesticides, some of which can only be applied by a certified applicator. The expense and/or toxicity of these pesticides may prevent many owners of backyard citrus from utilizing these controls. Backyard citrus owners may also be less likely to monitor their trees for psyllids or signs of greening, and backyard citrus owners may be less likely to remove a tree with signs of greening. Thus, backyard citrus may act as reserves for the Asian citrus psyllid and sources of new infections in commercial citrus. A survey of homeowners will gather data on their knowledge of the Asian citrus psyllid and greening, their current monitoring and/or treatment practices, and their predicted actions, in the event that they detect psyllids or greening in their trees. Using existing data on greening and potentially newly collected data, I will examine if and how backyard citrus and the existence of untreated and infected trees affects nearby commercial citrus growers. This project will include an evaluation of various policies that could be used to address spatial externalities. These include negotiation between growers within a region, the creation of pest management districts, and the implementation of a pesticide tax. The policies will be evaluated for efficiency and ease of implementation.