Pesticide Use Indicators

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Introduction

The most common metric of “pesticide use” is the pounds of active ingredient applied in a given year on an acre of a specific crop, and/or across all acres of a crop, and/or across all crops in a geographic region (a farm, county or state, nation, continent, the world).

Pesticide use in the U.S. is most often reported by state, or nationally, e.g. on all acres of corn in the nation, or all corn acres in Iowa.  Pesticide use data are available down to the county level from two sources in the U.S.: California-specific data from the California Department of Food and Agriculture, and nationwide data from the U.S. Geological Survey for 1992-2012, and preliminary estimates for 2013-14.

Around the world, use data are reported in pounds or kilograms of active ingredient applied, rather than pounds or kilograms of formulated products. Virtually no pesticide active ingredient is applied in a 100% pure form.

Adjuvants and surfactants are combined with the active ingredient to help sustain the active ingredient in the proper state (solid, liquid, gas), to help assure it sticks to plant leaves even if it rains, to accelerate the penetration of the active ingredient into plant tissues, or to protect the active ingredient from normal degradation processes driven by sunlight, rain, and air.

The concentration of active ingredients in formulated, ready to use pesticide products, typically ranges from a few percent, to as high as 75%, and occasionally higher. Formulated, brand name products are often then further mixed with water or liquid fertilizers, and then sprayed. The pounds of pesticide active ingredient applied in such common application scenarios are a tiny fraction of the volume of spray material applied per acre.

There are 10 distinct pesticide use metrics that are used to quantify pesticide application depending on the type of reporting that is called for. They are grouped on this page and discussed based on the type of measurement they represent.

Rate of Application Metrics

The first three important metrics of pesticide use are related to rates of application:

  1. Average “One-time Rate of Application” of active ingredient on an acre/hectare of a given crop;
  2. Average “Number of Applications” made with a specific active ingredient on a crop in a production cycle (usually a calendar year); and
  3. “Rate per Crop Year,” which is the average rate of application per production cycle, calculated as (average one-time rate of application) multiplied by (average number of applications).

Trends in metric #3 — “Rate per Crop Year” — across widely applied pesticides are critical in understanding changes in the pounds or kilograms of pesticide active ingredient applied.  This is because, since the early 1980s, the pesticide industry has focused on identifying new modes of action that are highly specific to target pests and effective at low-dose rates.  Such active ingredients typically target specific metabolic, biochemical, physiological, developmental, or reproductive processes in target pests.

The industry has been successful for the most part in this quest. One common outcome has been commercialization of new active ingredients that are effective even when applied at low, or even exceptionally low rates per acre/hectare. Hence, it is useful to track over time two other metrics that are related to “Rate per Crop Year” – Number of a.i.’s Applied at < 0.1 pound/acre; and, Percent of acres treated with an a.i. applied at < 0.1 pound/acre.

It is worth highlighting that most of the widely used, high-dose pesticides applied by farmers in the 1980s have been replaced in the intervening years by moderate, low, or very low-dose active ingredients. And as a result, pounds applied have declined, whether measured per acre, by crop, or across all crops. But unfortunately, this reduction does not mean that farmers have become less reliant on pesticides.

Measures of the Extent of Use

Pesticide impacts on the environment and human health are clearly a function of how widely and often a pesticide is applied, regardless of the rate at which it is applied on a given field. Accordingly, it is also important to take into account how widely and frequently a pesticide is used on a given farm, on a crop, and/or across all crops in a region.

Four additional, key metrics are needed to track the frequency and extent of use of a given pesticide:

  1. “Percent Acres Treated” is the percent of the acres of a given crop in a region that is treated with a given pesticide;
  2. “Number of Acres Treated” is the number of acres of the crop treated one or more times with a given pesticide, calculated as the (percent acres treated) multiplied by (total crop acreage);
  3. “Acre-Treatments” takes into account both the percent of acres treated and the average number of applications with each active ingredient applied, and is calculated as (acres treated) multiplied by (number of applications) made with a pesticide on the given crop; and
  4. “Pounds Applied” is the total pounds of active ingredient applied per production cycle on a given crop, or across all crops or sets of related crops (i.e., fruits or small grains).

These seven metrics represent a “Minimum Data Set” (MDS) for tracking use of a specific pesticide on a given crop. This MDS can be applied to a pesticide applied on a field, on all acres of a specific crop on a farm, and all acres of a crop across all farms in a county, state, province, region, nation, continent, or worldwide.

But the impact of pesticide use on farm production costs, the environment, the emergence and spread of resistant pests, and pubic health is driven by the total number of pesticides applied on a given field, farm, and across all farms. Accordingly, additional pesticide use metrics are needed to take into account how many different pesticides are needed to bring a crop to harvest in a given production cycle.

Limits of “Pounds Applied”

While data on the pounds of pesticide active ingredient are an essential part of the information that must be available to track pesticide use, costs, risks, and benefits,  “pounds applied” by itself can be a miss-leading indicator. This is because, in general, most people assume that more/fewer pounds applied equals greater/reduced potential for adverse impacts on the environment and public health. But this is often not the case.

Some herbicides like atrazine, s-metalochlor, acetochlor, and pendamethalin are applied at rates of around 1.0 pound of active ingredient per acre, while others are applied at rates below 0.01 pound. The majority of herbicides on the market today are applied at rates between 0.1 and 0.5 pound per acre.

The same is true of insecticides. Many older insecticides like DDT, carbofuran, oxamyl, and endosulfan were applied at rates around 1.0 pound per acre. Most relatively high-dose insecticides have been displaced by lower-dose, synthetic pyrethroids and neonicotinoids, as well as a host of newer insecticides with novel modes of action.

The major limitation of “pounds applied” as a stand-alone indicator of pesticide use is the absence of any consideration of potency, or biological activity in terms of altering pest population dynamics.  This notion of “potency” of a pesticide is often referred to as “activity,” and highly active pesticides are applied at lower doses than most other pesticides registered for use against the same crop pests.

A second important limitation of pounds applied per acre of an active ingredient is that some pesticide products are applied once per season, while others are applied multiple times. In addition, because of the need to go over fields more than once in order to apply various fertilizers and pesticides, some farmers will split a normal per acre application rate into two, one-half dose applications.

Accordingly, it is important to focus on pesticide use rates per crop year, taking into account all applications of a given pesticide on a given crop field in that year, or production cycle. The focus needs to be on an annual production cycle, instead of a calendar year, for crops like winter wheat that are seeded in the fall of one year, and harvested in the early summer or fall of the next year.

Measures of Total Use by Type of Pesticide

Typically, pesticide use data and trends are studied by major type of pesticide, and the categories of pests targeted by pesticides. The three major categories, and their corresponding type of pesticide, are: weeds (herbicides), insects (insecticides), and plant diseases (fungicides). These three major types of pesticides are often referred to as H/I/F.

For each major type of pesticide, there are three essential metrics needed to account for aggregate pesticide use. These can be quantified per acre, on a field, across all fields on a farm, and/or in a county, state, region, nationally or globally:

  1. Average “Number of Active Ingredients Applied” per acre/hectare to bring a crop to harvest in a given production cycle;
  2. Average “Number of Acre-treatments” made with an H or I or F on an acre producing a given; and
  3. “Total Pounds Applied” of H/I/F active ingredient applied on the average acre in a production cycle (sum of pounds applied across all H/I/F active ingredients used on a given crop).

Over the last several decades in most years and regions, farmers have managed weeds, insects, and plant diseases with one or two active ingredients on most fields, and often none. Until very recently, soybeans, for example, were never treated with fungicides or insecticides, and corn was rarely treated with fungicides. But nearly 100% of the conventionally managed acreage of both crops has been sprayed with herbicides annually. For decades, most conventionally managed fruit and vegetable crops, on the other hand, have been sprayed with 1-3 herbicides, 2-5 insecticides, and 2-4 fungicides.

Slipping pesticide efficacy in a pest management system, perhaps driven by the emergence of resistant pests, is almost always accompanied by an increase in the number of active ingredients – and modes of action – applied on a given field. This is why tracking changes in the number of active ingredients applied on a given acre is so important.

But sometimes when farmers face new or tougher-to-control pests, they respond by applying a second application of an active ingredient sprayed previously in the same production cycle. This additional application would not be picked up in the metric “number of distinct active ingredients applied.” For this reason, metric nine above is needed. It takes into account both multiple applications with a particular pesticide, as well as applications with a new active ingredient.

Pesticide use data from the USDA show clearly that pesticide use intensity has increased much more significantly than suggested by some indicators, such as percent acres treated and total pounds of active ingredient applied.

Measures of Total Pesticide Use

Farmers strive to track and manage pests in ways that protect profit margins. This requires keeping crop yield and/or quality loses to a minimum, while also minimizing the cost of pest management systems. On most conventional farms, buying and applying pesticides account for the lion’s share of total pest management system costs.

Adverse pesticide impacts on the environment – water and soil quality, birds and fish, earthworms, biodiversity, and non-target organisms like pollinators or other plants – are driven by total pesticide use, not just the use of a specific active ingredient.

Likewise, public health impacts from pesticide use are the sum of impacts caused by exposures to specific active ingredients, as well as interactive and sometimes synergistic effects stemming from exposures to multiple pesticides during a given time period.

Accordingly, a pesticide use minimum data set needs to also take into account total pesticide use across all H/I/F applied. If other categories of pesticides are applied, like soil fumigants, plant growth regulators, or desiccants, these too need to be added to the total quantity of pesticide active ingredient applied.

The metrics needed to measure total pesticide use are simply aggregate versions of the above 10 metrics, where use of all types of pesticide applied are added together. These metrics can be expressed per acre at the farm level, across all acreage of a crop grown in a region, across all crops of a given type (vegetables, fruits, grains), and/or for all crops.

Measuring Other Impacts Associated With Pesticide Use

There are four other important consequences stemming from pesticide use that warrant tracking: economic impacts, environmental and public health risks, potency in terms of impact on target pests, and diversity in modes of action (key metric linked to resiliency and prevention of resistance). Each is briefly introduced below, and will be addressed in future postings.

Economics

The cost side of the economics of pesticide use is straightforward. The above 10 indicators can be converted to cost estimates by simply adding the cost of active ingredients per pound into an analysis, and multiplying pounds applied of a specific active ingredient by its cost per pound. Typical application costs per acre-treatment must also be added.

The quality of control, and the length of control, also impacts the economic performance of pest management systems, and hence the return to pesticide expenditures. Quantifying pesticide efficacy, and the “quality” of control, entails determining whether and to what extent either crop yields or crop quality has slipped, and then translating such slippage into lost farm receipts.  Lower receipts reduce profits, and in some circumstances, are severe enough to trigger overall economic loses on a per acre basis.

Quantifying Risks

Projecting or monitoring the environmental and public health impacts of pesticide use requires often-complex risk assessments that take into account:

  • When, how often, and how much pesticide is applied;
  • The formulation of the pesticide applied and how it was applied;
  • The persistence and environmental fate of applied pesticides;
  • Levels reached in non-target environments (water bodies, the soil, animal and human food); and
  • Exposure levels and timing of exposures impacting non-target organisms.

Potency

Far too little attention has been directed toward monitoring changes in the total “kill” power needed within a pest management system to bring a crop to harvest.  The use of the term “kill” in this context encompasses lethal modes of action, but also others that reduce pest populations by disrupting reproduction, discouraging feeding, or eliminating essential habitat or sources of nutrition.

Obviously, the ideal pest management system requires no or very little outside help, and controls pests through an integrated set of preventive measures, often referred to as Integrated Pest Management, or IPM. The majority of land managed organically, for example, is not treated with any pesticide.  In most years and regions, a share of conventional hay and small grain crops are also not sprayed with any pesticide.

When farmers have to increase the total potency of herbicides, insecticides, or fungicides applied in a given crop production cycle, it is a sign that for some reason pest infestations are growing more difficult to manage, and hence pose greater risk of triggering economic losses, or environmental and public health risks.  The three most common causes of slipping pesticide efficacy are:

  • The emergence and/or spread of less sensitive, or fully resistant pest phenotypes;
  • A reduction in the health of the crop because of changes in the genetics of the seed, changes in soil health, or increases in seeding rates; and
  • A new, exotic pest becomes established that was not previously in a crop production region.

Diversity in Modes of Action

The best way to promote resistance in target pest populations is to rely heavily on a single pesticide, or pesticides that work through a common mechanism of action. For farmers that chose to rely predominantly on pesticides in their IPM systems, the best way to prevent resistance is to apply active ingredients in secession, or together, that work through multiple modes of action.

Since most of the environmental and human health risks stemming from pesticide use are directly linked to how widely and how often a particular pesticide is used, spreading out the burden of control over multiple families of pesticide chemistry is a sound tactic that will help avoid significant impacts on vulnerable, non-target organisms. It’s a way to spread out the risk of adverse impacts, so that if one use of a pesticide does prove damaging in some unforeseen way, the collateral damage is contained and more easily avoided in the future.

These are the major reasons why diversity in the use of pesticides is desirable, and why measuring the homogeneity of overall pesticide use targeting a particular type of pest is so important.  When farmers rely on just one mode of action to control a class of pests, trouble is likely just around the corner, as in the case of crops genetically engineered to tolerate applications of glyphosate.