Using pre-emergent herbicides helps to prevent the majority of weeds, by stopping weed seeds before they have a chance to grow. However, some common weeds will still germinate, no matter how many pre-emergent treatments you apply; this is where a post-emergent herbicide is required. A post-emergent herbicide is a chemical weed killer, which serves the purpose of eradicating weeds that have germinated, and are actively growing.
List of Common Weeds (Scientific Names in parenthesis):
• Milkweed (Asclepias syrica)
• St. John’s Wort (Hypericum perforatum)
• Purple Nutsedge (Cyperus rotundus)
• Mullein (Verbascum thapsus)
• Plantain (Plantago major)
• Chickweed (Stellaria media)
• Dandelion (Taraxacum officinale)
• Chicory (Cichorium intybus)
• Queen Anne’s Lace (Daucuscarota)
• Common Purslane (Portulaca oleracea)
Brief Overview of Non-Selective and Selective Post-Emergent Herbicides
There are different types of post-emergent herbicides that you can use to get rid of undesirable plants (weeds); they can be either selective or non-selective. Non-selective herbicides kill several types of plants; however, selective herbicides kill specific plants, without seriously disturbing surrounding plants. An example of non-selective herbicides would be products such as Roundup, Finale, GroundClear and Brush Killer. Usually these products kill all vegetation (also known as total vegetation killers). Selective herbicides would include products such as Image, and Vantage.
Caution is required when applying herbicides. It is important to read, and follow pesticide label directions exactly as directed. Here are 10 tips to assist you in applying chemical herbicides:
- Always wear protective gloves and clothing, when handling chemical herbicides.
- It is not necessary to douse (wet thoroughly) the entire plant when applying treatment.
- Spot treatments should be sufficient in cases of small weed infestation. Care is required when spot treating, so that you apply the herbicide on the weed plants, and not on desirable plants (plants you want to keep).
- If you are applying a liquid herbicide with a sprayer, make sure it is not on a windy day, because strong winds (and even light winds) can blow chemicals on your other plants. You will achieve the best results if you apply during a sunny day, when the temperature is above 60 Degrees Fahrenheit. Some landscapers suggest even warmer temperatures.
- Take measures to protect your desirable plants when applying herbicides. You may cover the plants that you want to keep with cardboard or plastic, to make sure the weed killer does not touch them by accident.
- If you sprayed the wrong plants in error, the best way to counteract the effects is to apply water to the plant immediately, to wash off the herbicide.
- Most weed killer labels suggest that you hold off mowing your lawn for approximately 7 days after applying herbicide treatments.
- Make sure you read label instructions to see if that particular plant killer can be used near vegetables grown for consumption.
- Do not allow pets near treated areas for at least 48 – 72 hours, just to be safe.
- Wash hands thoroughly after using chemical weed killers; change clothes and shoes, just in case any chemicals made contact.
If you do not feel comfortable applying herbicides in your garden, hire a professional to do it for you.
Joseph C. Neal – Postemergence, Non-Selective Herbicides for Landscapes and Nurseries – NC State University
Lawn & Landscape Weeds – Landscape America
Scientific Name Index – Virginia Tech Weed Identification Guide