Figure 1. What happens to pesticides following their application, and the potential for exposure to users, has been studied extensively. Registered pesticides, when used according to label, are deemed safe for the end user. However, this remains a complicated subject and there is not one clear answer for all questions.
Proper control of weeds, insects and diseases is an important and necessary component of any turfgrass management system. On athletic fields this is not only for the purpose of aesthetics but also from the standpoint of insuring that the turfgrass system provides proper traction and footing which hopefully reduces the possibility of injury to the users of the field. Depending on which pest you consider, pesticides are either a tool that can be used to make the management of turfgrass pests easier (for example, dandelions and other tap-rooted weeds), or perhaps they are the only plausible way of dealing with a particular pest (for example, grey leaf spot or another pathogen).
The use of pesticides became widespread on turfgrass systems in the 1960’s and 1970’s and the controversy associated with their use soon followed. Because of this controversy, there are many laws, that are quite variable, that govern whether and what pesticides you may use. Depending on where you are reading this article, you may be free to use legally registered pesticides, or the list of products may be restricted, or you may not be allowed to apply anything for the control of pests on the turf. In those areas where you are legally permitted to apply pesticides, in many cases you may be or have been faced with the issues of speaking with concerned citizens/users of the fields regarding the types of products that you are applying and any risks associated with their use.
Pesticide use has and continues to be a controversial issue. With any controversial issue there will be people who a) don’t care, b) think all pesticides are bad no matter, or c) have some concerns about whether the use of pesticides on your fields is appropriate and responsible. This month’s article attempts to address some of the more commonly encountered questions that I have heard over the years that people have asked about pesticides and then I will attempt to provide insight into why the question is asked and maybe even some possible responses.
Question: What are you spraying?
You are legally required to be able to answer this question. Not only the name of the product but also have available the label and safety data sheet (SDS) for inspection. Given the controversies around pesticide use it’s perfectly normal to hear this question. If they approach you while you are making the application then direct them off of the field before speaking with them. I find that this happens more often when an application is being made that is a granular formulation. I also find that it’s a good idea to be able to explain in laymen’s terms what the active ingredients are in the product that is being applied and what the specific target pest is. It’s also a good idea to explain what might happen to the field if the pest is not controlled.
Question: Is it safe for me (or my kid) to be around what you are spraying?
This is a really hard question to answer for no other reason than that the word “safe” means something a little different to everyone. The other part of the answer to this question depends on how long after the pesticide was applied is the exposure occurring.
The easy answer is to state that since you are using a registered pesticide according to its label directions that, after the reentry period, users should be reasonably safe. Personally I think it is risky to get into a lot of detail because of the risk of miscommunication. However, a bit lengthier version of an answer to the question follows:
All pesticides have some level of toxicity because, as the name implies, they are designed to kill something. The actual risk associated with a particular product depends mainly on a couple of things. One is its toxicity and the other is a person’s exposure to it. A German physician by the name of Paracelsus, way back in the 1500’s, basically summed it up by saying, and I’m paraphrasing, that everything is toxic if you are exposed to enough of it. So, for example, things like oxygen and water have been known to cause death.
We use a standardized measure called the LD50 to express a substance’s toxicity. It is defined as the lethal dose that is necessary to kill 50% of the test subjects. Typically, rats are used to approximate human response. It is measured in milligrams of substance per kilogram of body weight. Because of that, the lower the LD50, the more toxic the substance is, because less of it is required to cause death.
If you look up LD50 values for the active ingredients in our pesticides that are registered today and compare it to some other things we encounter in life they are usually not spectacularly more toxic. For example, the reported LD50 of glyphosate is 5180 mg/kg. Compare this to things like table salt (3320 mg/kg), bleach (2000 mg/kg), caffeine (200 mg/kg), or gasoline (50 mg/kg). I picked glyphosate on purpose because it has one of the highest LD50 values (so it’s one of the least toxic) of any pesticide we apply. This should make sense if you look at how it works. It acts to inhibit the formation of branched chain amino acids. Plants need to be able to do that and we do not. Now, a couple of caveats to this line of thinking: 1) there are other substances in formulated pesticides that might be more toxic than the actual active ingredient and 2) there are other active ingredients that are more toxic than glyphosate. The signal word on the pesticide container is the guide to its toxicity. For example, most formulated products containing glyphosate carry a caution label, which means the LD50 is between 500 and 5000 mg/kg. There are many pesticides that are more toxic, and so they will carry a warning (LD50 between 50 and 500 mg/kg) or a danger (LD50 less than 50 mg/kg).
There are many things around the house that are just as toxic as pesticides, such as antifreeze, motor oil, gasoline, battery acid, bleach, and household cleaning products. As with any of those products, pesticides should be respected and we should be careful when we use them. Just like gasoline, pesticides can be dangerous when used improperly but are considered reasonably safe when used correctly.
A Potential follow up Question/Comment: Fair enough, but that tank seems pretty big, which mean you are applying an awful lot of material
Another important factor with pesticide safety is exposure, both short term (acute) and long term (chronic). The pesticide label contains a section called Hazards to Humans and Domestic Animals that gives an overview of the risks.
With acute exposure, unless the user comes into contact with the concentrate they are unlikely to be poisoned by the pesticide. With one of our common herbicides, a 200 pound person would have to ingest about 4 gallons of formulated product to have a 50% chance of dying, which is not very likely.
Having said this, people can report symptoms such as dizziness, nausea and headaches as a result of exposure. On the product label it states the amount of time necessary following application before the treated area can be reentered. During this time the residues dry and become bound to plant, soil and organic matter.
Most evidence available in the literature shows that bound pesticide residues do not come off of (dislodge) from organic matter very easily. This varies by active ingredient. The risk becomes greatly reduced, but not completely eliminated, which may lead to:
Question: I’ve read or heard that a lot of pesticides are suspected of causing cancer (or other health problems)?
This is also a tough question because sometimes things we think are safe, including certain pesticide active ingredients, we later learn are not. The effects of chronic exposure (long term exposure to very small amounts) are much more difficult to study. And even if a product does pose a risk, determining if the risk is greater than that encountered due to exposure to other things in life (sunlight, air pollution, contaminants in drinking water, etc.) is in some cases nearly impossible.
In order for a product to be registered, it must be approved by the EPA. In order for this to happen, the product must go through over 100 different health, safety and environmental tests to assure that the product will not cause undue harm. This might seem like a relatively simple thing, but each one of these tests might involve research experiments in several states over a period of years. The bottom line is that it can take many years and millions of dollars to conduct all of the testing necessary to get a product registered for use.
Pesticides are also reviewed and if there is evidence that a particular active ingredient poses a risk, it is usually taken off the market. But, again, this can be tricky because with certain products there may be some evidence that the product causes health problems while other studies indicate it does not. The best course of action, once again, is to follow the label and laws that govern the application of the particular pesticide in order to minimize the risk.
Question: What happens to the product after you spray it?
In order for a product to be registered, the chemical company must show that the pesticide poses minimal risk to the environment when used according to label. Many of the pesticides labelled for use in turfgrass bind to organic matter in the soil, which minimizes or prevents leaching. The pesticide is then broken down into harmless compounds by microorganisms. Certainly this is a very gross simplification of pesticide fate processes. There are many other ways in which pesticides interact with the environment and are ultimately broken down. But, again, in order to be registered, the chemical company must show that the product when used according to label does not pose a risk of environmental contamination.
Question: Does the pesticide that you spray harm bees (or wildlife, or fish, or birds)?
All registered pesticides must be assessed for potential hazards to wildlife, including mammalian, avian and aquatic. Pesticides with too high of a risk are either classified as restricted use or are denied registration.
Bees are a different story. Certainly this has gained much attention and, as pollinators for many of our food crops, for good reason. Most of the pesticides we apply are harmless to bees. Harm due to the application of an active ingredient that is implicated in potentially causing problems can be greatly reduced if spraying is avoided on areas that contain clover when the clover is in bloom. This is one example of management recommendations that have evolved in order to help reduce potential non-target affects from the use of those insecticides.
The bottom line
The use of registered pesticides does carry some risk. However, if you follow the label exactly and follow all rules governing the application of pesticides in your location then the use of registered pesticides is considered reasonably safe. Users may ask questions about your use of pesticides. Thoughtful, educated answers can, in many cases, satisfy the concerns of end users of your fields.
An accompanying Power Point presentation to this article can be accessed here:
Author: Dr. Dave Gardner, Professor of Turfgrass Science at The Ohio State University