Herbicide Use and Safety for Homeowners

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By Adam Smith

The forsythia has begun to bloom, indicating that it is time to put down a pre-emergent herbicide for crabgrass. We have received a few questions about herbicides at the extension office in the last couple of weeks. Hopefully, this information will clarify some of the confusion.

Despite our best efforts to maintain well-mulched beds and gardens and dense healthy lawns, weeds always seem to find a way. Weeds are excellent at finding the weak links in our yards and gardens and have evolved to thrive under limited resources. In situations where weeds pose a threat, a little bit of extra help might be needed. Herbicides can be excellent tools for weed control; applied appropriately, they can provide sufficient weed control while posing minimal risks to homeowners and their families. In order to do that, it is important to understand how herbicides work and how to safely apply them.

Herbicides are generally separated into various categories based on when they can control weeds and how they interact with weeds once applied. Herbicides can either be pre-emergent or post-emergent herbicides. Preemergent herbicides prevent weeds from emerging from the ground by inhibiting different growth processes, thereby killing the plants. A very common preemergent herbicide type are those that prevent crabgrass from emerging in our lawns. Postemergent herbicides are applied after weeds have already emerged and only work by making direct contact with the weeds. Some post-emergent herbicides are systemic herbicides, whereupon application, these herbicides are absorbed by the weeds and are moved around inside the plant (a process called translocation). Other post-emergent herbicides are contact herbicides, meaning that they only work on the plant parts that receive actual herbicide solution. By way of example, the herbicide glyphosate (the chemical in Roundup and other brand names) is a systemic herbicide. Once applied, glyphosate is absorbed by the weeds and relocated to the growing parts of the plants where it inhibits plant growth and slowly kills the plant; this is why weeds treated with glyphosate can take several days to show evidence of treatment. Furthermore, herbicides are either non-selective or selective herbicides. Non-selective herbicides will harm or kill all species of plants. A common example of a non-selective herbicide is the active glyphosate found in products like Round Up. Other herbicides are selective herbicides, meaning that when we apply these herbicides simultaneously to both desirable plants and weeds, the weeds will die while our desirable plants will live. An example of a selective herbicide are those herbicides that we apply to our lawns to control broadleaf weeds like white clover; our turf isn’t harmed and the weeds in our lawns curl up and die.

In order to apply herbicides (or any pesticide) safely, it is important to read the label. The label contains all relevant information regarding target weed species and application instructions and required personal protection equipment (PPE). The latter is of particular importance. Herbicides can enter the body in four ways: skin, eyes, mouth, and lungs. Skin contact is the most common cause of herbicide exposure. Every herbicide label will provide instructions for what articles of clothing to wear, what type of gloves are needed, and whether a respirator and eye protection are required. Following these instructions will allow you to handle herbicides safely. The label will also state the restricted entry interval (REI); the REI is a period of time where no one (humans and animals) should enter into the treated area. Additionally, all herbicide labels state its toxicity, describe the emergency first-aid measures necessary for the product in case of an accident, and proper storage and disposal. Reading and adhering to the label directions will ensure that your herbicide applications will be effective and safe.

If you have any questions regarding herbicide use and safety, call N.C. Cooperative Extension, Catawba County Center at 828-465-8240 or stop by the office located at 1175 S. Brady Ave., Newton, NC 28658.