Reading Herbicide Labels

In the coming weeks, many homeowners will be applying herbicides for weed control in their lawns. We will be attempting to prevent the emergence of old enemy number one -- crabgrass -- as well as suppress a myriad of broadleaf weeds with postemergence products. Understanding the contents of herbicide labels is essential for the product’s safe and effective use.

Pesticide labels have been called "million dollar documents" for good reason. Before a pesticide receives its registration from the U.S. Environmental Protection Agency (EPA), the manufacturer is required to submit data from nearly 150 various testing procedures. These data provide the user with much of the information that is found on the label concerning the product’s use, safety and effects on the environment. As one would imagine, there is a tremendous amount of time and effort that goes into this process before we even see the product come out on the shelves of the local lawn and garden center.

Let’s review some of the information that is found on pesticide labels, particularly herbicide labels since these will be commonly used in the next several weeks. Because many of us have children and/or pets present in our landscapes, we will want to pay particular attention to the section regarding hazards to humans and domestic animals. This part of the label includes precautionary statements indicating specific hazards, routes of exposure and precautions to be taken to avoid human and animal injury. You will see statements such as "avoid breathing spray vapors, spray mist or dusts" and "do not get on skin or clothing." Based on these types of effects, the label will then instruct you about special clothing or equipment to wear while handling and applying the product. It may mention that the user should wear coveralls, protective eyewear, chemical-resistant footwear, chemical-resistant gloves or whatever garment necessary to protect from exposure to that product. Look in this same section of the label to see if there are concerns for when it is safe for children and pets to resume activity in the treated area. Some of the herbicides formulated as dry granules will have label statements such as "do not enter until dusts have settled." Similarly, labels of liquid products applied as sprays may precaution anyone from entering the area until "sprays have dried."

The largest body of information within the label are the directions for use. Directions for use include the following information: 1) The type of site that may be treated with the product. Some herbicides are not labeled for application to certain turfgrass species, or even certain cultivars, because of excessive injury problems. With many of our postemergence herbicide products particularly, there will be strong warnings against applying or allowing drift to contact desirable plant foliage. It’s important to know what you’re going to treat before you even purchase the product. 2) The amount to apply per unit of area or mix volume. In most cases, turfgrass herbicide rates will be stated in terms of amount of product per 1,000 square feet. Many of the granular products on the market today have a table within their label that will specifically state the setting for most commonly used push spreaders to apply the correct amount per 1,000 square feet. Liquid herbicide labels will generally instruct you as to how much to mix per gallon of water to apply through a hose-end or hand-pump sprayer. 3) The timing and frequency of application. There are herbicides, particularly postemergence products that suggest sequential applications of the product will provide optimal control of the target weeds. These same labels will tell you how many days to wait from the first application to the second and how many times per season you may apply the product. If you’re planning to reseed or overseed in the late summer or early fall, pay close attention to the interval that is given from application, regardless of pre- or post-herbicides. Some of these materials can persist to interfere and limit your success of seedling stand establishment in the fall. 4) The pests controlled. With herbicides, a listing of specific weeds will be provided that should be controlled if applied correctly and if the weather cooperates. If you are trying to control species of weeds not listed on the label, there is no company guarantee that the product will be effective.

There is a tremendous amount of information on the label. You should read the label at least four times: before purchasing to ensure that it is the one you need, before mixing to ensure the proper concentration, before applying to ensure the proper use and before storing or disposing of the empty container. If you’d like more detailed information on pesticide labels, obtain MU Guide G1911, Understanding the Pesticide Label from your local University Outreach and Extension Center or find on-line at http://muextension.missouri.edu/xplor/agguides/agengin/g01911.htm.

Fred Fishel, Extension Pest Management/Pesticide Training Coordinator, UMC (573) 884-6361.