California Agriculture

Insecticides have long been important tools for California farmers to combat agricultural pests. By 1995, organophosphate (OP) insecticides such as chlorpyrifos, azinphos-methyl, methamidophos, phosmet and diazinon accounted for an estimated 34% of worldwide insecticide sales, and they are widely credited with allowing large yield increases in commercial agriculture. The U.S. Food Quality Protection Act (FQPA), signed into law in 1996, established a new human health–based standard that “reasonable certainty of no harm will result from aggregate exposure to the pesticide chemical residue.” When the FQPA was passed, 49 OP pesticides were registered for use in pest control in the United States; since then, many uses have been canceled and others are expected to be lost, with particular significance for California growers. A number of alternative pest-control products and strategies are available, with varying degrees of effectiveness and cost. Research and development of control measures to replace OP insecticides must be pursued to maintain an economically viable state agricultural industry.

Synthetic pyrethroids and neonicotinoids are the most readily available alternatives to the organophosphate and carbamate insecticides. Pyrethroids have become widely used in California, and problems with insecticide resistance and nontarget impacts have already been identified. Neonicotinoids are a new class of insecticide with uses only now being realized. Managing insecticide resistance will be crucial to preserving these new materials as organophosphate uses are lost.

The direct management of insect pests using pheromones for mating disruption, or “attract and kill” approaches, can provide excellent suppression of key lepidopteran pests in agriculture. Important successes to date include codling moth in pome fruit, oriental fruit moth in peaches and nectarines, tomato pinworm in vegetables, pink bollworm in cotton and omnivorous leafroller in vineyards. Large-scale implementation projects have yielded significant reductions in pesticide use while maintaining acceptably low crop-damage levels. Because of some difficulties with high populations of pests, these programs should not be viewed as stand-alone strategies but rather as one tactic within a suite of integrated pest management options.

Biological controls (the use of natural enemies) and cultural controls (the modification of cropping practices) provide valuable alternatives to organophosphate insecticides (OPs) for the suppression of major arthropod crop pests in California. We discuss the successes and limitations of these two approaches with regard to tree fruits and nuts, vines, and field and row crops. For example, a historic success story is that the cottony cushion scale remains innocuous in citrus production, more than 100 years after its successful suppression by the vedalia beetle. More recently, growers’ use of groundcovers and road maintenance helps keep dust down on orchard roads to limit the buildup of web-spinning mites, and good vineyard management is now synonymous with cultural controls for grape pests. Although such alternatives may not always be as effective and predictable as conventional insecticide programs, recognition that partial suppression can greatly reduce the need for OPs will lead to the more widespread adoption of alternatives.

A number of novel insecticides have recently been registered for insect control in agriculture. A major advantage of these new products is that they act on insect biological processes that humans do not experience, such as molting. Many also have greater selectivity to target specific species, so they are less likely to harm natural enemies when compared with the broader spectrum organophosphate, carbamate, neonicotinoid and pyrethroid insecticides. Such novel insecticides currently in use include four targeting lepidopteran pests, three targeting sucking insects, one specific to dipteran leafminers and one insect growth regulator that controls a wide range of insects. One negative aspect of these insecticides is that because of their narrower range of activity — controlling only a limited number of pests — growers may need to apply additional pesticides for secondary pest groups that have poor biological control, increasing the total number of treatments per acre and total pest-control costs.

The insect and mite control potential of natural and biological toxins has been recognized for several centuries. Bacteria, viruses, protozoa and fungi are the primary groups of microorganisms known to reduce insect populations; they often occur naturally in fields and function as components of biological control. Beneficial nematodes are also being used for pest control, especially against soil insects. The isolation of toxic metabolic compounds from microorganisms continues to be a fruitful research area, although there are barriers to their successful marketing and distribution. Another, more controversial way to deliver these insect-specific toxins to the target pest is through genetically modified plants, such as those modified to express Bacillus thuringiensis (Bt) toxins. Oils and particle films also have important niche uses for pest control.

The California Department of Pesticide Regulation (DPR) restricts pesticide use to reduce negative impacts on human health and the environment. The DPR implemented methyl bromide use regulations in 2001. Our study demonstrates that the estimated 2001 costs of these regulations for the California strawberry industry were quite substantial (more than $26 million total), equivalent to roughly 25% of estimated industry returns over total cash costs in 2001. These impacts were unevenly distributed across growers. Growers with small fields in urban areas had higher per-acre costs than growers with large fields in agricultural areas.