How to Manage Pests

Interactive Tools and Models: About the Dormant Spray Alternatives Calculator

Organophosphates (OPs), especially diazinon and chlorpyrifos, have been routinely detected in the Sacramento and San Joaquin River watersheds coincident with storm events which follow their application to dormant orchards. These studies have been conducted by both federal and state agencies, and indicate that small invertebrates are killed when exposed for even short periods to OP levels measured in the two watersheds during winter. These invertebrates are indicators of the health of aquatic food chains and serve as primary food for many larval and juvenile fish. The magnitude and duration of the insecticide-caused toxicity following the mid-winter storm events is such that it is a violation of the Central Valley Regional Water Quality Control Board Basin Plan water quality standard for toxicity. In 1998, the State of California placed the Sacramento River and the San Joaquin River, as well as the associated Delta/Estuary on the Clean Water Act 303(d) list of impaired waterways in part because of elevated levels of diazinon and chlorpyrifos from dormant spray orchard runoff. These listings necessitate the development of Total Maximum Daily Loads (TMDLs). TMDLs will restrict the quantities of the OPs coming off of specific areas. Diazinon and chlorpyrifos are widely used in California for a variety of urban as well as other agricultural applications, and all uses are subject to restrictions stemming from the TMDL limitations. The California Department of Pesticide Regulation (DPR) has the authority to impose regulatory restrictions on these pesticides at any time.

Selecting pest control options that reduce aquatic concentrations of OPs sufficiently to prevent toxicity may prevent regulatory action to restrict or eliminate the use of these materials. One option to prevent the movement of OPs applied in the dormant season to waterways is to employ best management practices (BMPs) when utilizing the OP and oil dormant spray. Among possible BMPs are proper mixing and loading of pesticides, sprayer calibration, spray drift avoidance, and container and waste water disposal. These are common-sense practices that are already employed by growers. BMP cultural tactics include planting vegetation strips along the edges of orchards and creating berms to contain water on site. Maintaining an oprchard floor vegetation cover may also be beneficial to reducing OP movement offsite. There are, however, other viable alternatives to the dormant season use of OPs that can be used to control the same pest complex on almonds and stone fruits. This pest complex includes aphids (in plums and prunes), peach twig borer, San Jose scale, and eggs of the European red mite and brown mite.

The dormant OP and oil sprays have been used for many years, and have provided acceptable control of the pest complex often with a single spray. In some cases, this eliminated the need to spray for these insects and mites during the season. The viable control alternatives to the OP and oil dormant sprays are more complicated to use, less familiar to growers and pest control advisors, require careful monitoring, and often require more than one distinct action to achieve a similar level of pest control. Some of the alternatives are more pest specific, and others increase the possibility of spider mite outbreaks later in the season. Cost is also a concern because of the complexity of the decision process and the possibility that multiple actions could be necessary.

This calculator is drawn from the final report of a study sponsored in part by the State Water Resources Control Board intended to identify possible alternatives to the OP and oil dormant sprays used by almond and stone fruit growers. The report was authored by Frank Zalom, Michael Oliver, and David Hinton of the University of California. It is available from Victor de Vlaming, State Water Resources Control Board, Division of Water Quality, 901 P Street, Sacramento, CA 95814.

Cost of implementing a practice is a major consideration for growers. The purpose of this calculator is to identify potential costs associated with viable alternatives to the OP and oil dormant spray. The only input variables considered are those which directly relate to control of the pests which are targets of the dormant spray. These include:

• monitoring cost
• number and cost of pesticide(s) that would be used instead of the dormant OP and oil spray to control the target pests during the dormant season, during bloom or in season
• number of in-season sprays over and above those which would normally be applied
• number and cost of miticides that would be applied to control spider mites resulting from the sprays intended for the target pests over and above those sprays which would normally be applied for spider mites when the dormant OP and oil spray was used
• application method

Total cost for each alternative will vary by the

• per acre or per unit cost of the service or product utilized
• the rate of materials applied
• by the number of sprays, if any, made in response to pest abundance as indicated by a monitoring program

Default actions and values are provided for each of the required variables, and the user of the calculator is expected to review and change the defaults as appropriate to their orchard. Costs associated with control of other insects, mites, plant diseases, and nematodes are not considered, nor are possible environmental or social costs.

What the calculator will do:

The calculator allows the user to choose an alternative to the dormant spray, and then fill in values for variables that are related to possible actions and costs that may be necessary if the OP and oil dormant spray is not applied every season. It is not expected that every possible action will need to be taken, as this will depend on pest abundance in the orchard and other factors that are specific to that orchard.

The calculator provides a general guideline for the thought process that must be followed to compare the costs associated with alternatives to the conventional dormant spray. The actions (including types and rates of products) and associated costs of the actions can be changed by the user and the calculator can be rerun so as to determine a range of possible costs of each alternative.

Many of the alternatives are similar, but they are presented separately to emphasize the key element differentiating the particular alternative from the others.

What the calculator will not do:

The calculator cannot predict the types of actions (e.g., need for a spray, type of material needed, number of applications, proportion ofthe total area treated, type of application equipment, etc.) that will be necessary in a given orchard. These are site specific and require knowledge of the orchard that can only be understood by the grower and pest control advisor, and the user is encouraged to change the default values as appropriate for his or her orchard.

The calculator is not intended to be used for all pest control decisions. It does not include insecticide, fungicide, or herbicide treatment actions or costs that are not directly related to the OP and oil dormant spray or a viable alternative to that spray.

The calculator mentions specific insecticides and miticides, and provides default rates, but the user is responsible for checking the legality of these for use in their orchard. The pesticide label is the law.

The practices included in the calculator are those which are considered to be most viable and do not include all possibilities.