Weed Management Options Which Reduce Pesticide Risk

Using Herbicides for Weed Control

Using Less Harmful Herbicides

Pesticides are designed to be toxic to their target organism, be it a weed, insect, or fungus. The impact of pesticides extends beyond their target organisms, however, and may include effects on farm workers, consumers, and the environment. Although regulatory procedures include reviews on the health and environmental effects of pesticides and are designed to minimize the impacts of pesticides on these non-target organisms, many people still have concerns about the effects of pesticides on human health and the environment.

Pesticides are not all created equal, however. The environmental impact of agricultural chemicals varies widely, and depends on a number of factors, including:

  • their level of toxicity to a variety of organisms;
  • acute and chronic effects on health of farm workers and consumers;
  • their persistence in the environment, on plant tissue, in the soil, and in organisms that consume them;
  • the potential for their escape from the application site by volatilization (entering the air), run-off or leaching;
  • the dose and number of applications typically required for the pesticide.

Although herbicides are designed to target plants, they can also be toxic to humans and wildlife. Herbicides vary greatly in their environmental impact, and more specifically, their toxicity and persistence in the environment. Farmers have the potential to reduce the pesticide risk by choosing herbicides that have less impact on humans and the environment.

Environmental Impact Quotients

Researchers at Cornell University have developed a system for quantifying the environmental impact of pesticides commonly used in fruit production in that region. This system, called the environmental impact quotient (EIQ), incorporates data on toxic effects of pesticides on mammals, fish, birds, beneficial insects and other insects, persistence of pesticides in the environment, and the risk of exposure. It combines a farm worker component, a consumer component, and an ecological component to come up with a value representing each pesticide’s EIQ. These EIQ values, together with percent active ingredient in the formulated product, and the application rate and frequency, can then be used to calculate total effects on the environment (including humans) in that agricultural system, allowing farmers to choose pesticides that are less harmful to the environment.

Although the equations used to calculate EIQ values in this study are based on fruit-growing agricultural systems, these values can still apply loosely to field cropping systems, even though many variables, such as farm worker exposure levels, would be different than in fruit production.

Table 1. Environmental Impact Quotients (EIQs) and field use ratings for several herbicides.

Herbicide Herbicide Group EIQ* Active ingredient Application rate Kg of product / ac Field use rating (EIQ x kg product/ac)
Metsulfuron-methyl (Ally) Group 2 16.67 60% 3 g/ac 0.0018 0.03
Clethodim (Select) Group 1 17.0 240 g/l 0.08 L/ac 0.0192 0.326
Quizalofop-P-ethyl (Assure) Group 1 51.7 96 g/L 0.15 L/ac 0.0144 0.744
Glyphosate (Roundup Original) Group 9 15.3 356 g/L 0.3 L/ac 0.107 1.64
Sethoxydim (Poast Ultra) Group 1 27.5 450 g/L 0.45 L/ac 0.2025 5.57

*EIQs taken from A Method to Measure the Environmental Impact of Pesticides, Table 2, List of Pesticides (Cornell University).

According to this method of classification, Group 2 herbicides are less harmful to the environment than many other herbicides, due to their low dose and low environmental impact. Herbicides which control similar weed spectra and have the same mode of action (for example, sethoxydim, clethodim, and quizalofop-P-ethyl) can have large differences in their EIQ and field use rating.


When possible, choose herbicides such as Group 2’s, which have a low dose and low environmental impact.



Kovach, J., C. Petzoldt, J. Degni and J. Tette. A method to measure the environmental impact of pesticides. Cornell University.