Is Broadleaf Weed Killer Safe for St. Augustine Lawns?

Weed and Feed

• Weed-and-feed products are supplied to St. Augustinegrass lawns in the spring. These products consist of fertilizer and herbicide. The herbicide used is chemically formulated to kill broadleaf weeds without harming St. Augustinegrass. However, gardeners may burn up their lawns if they use weed and feed during hot temperatures or apply an excessive amount of the product. In addition, weed and feed is best used if weeds populate the entire yard and not small patches, according to the University of Florida.

Pre-Emergent Herbicide

• Pre-emergent herbicides are applied before broadleaf weed seeds have had a chance to germinate. It is important for gardeners to apply pre-emergent herbicides right before soil temperatures favor weed seed germination. For example, dandelion seeds start germinating when soil temperatures are at least 50 degrees Fahrenheit, according to the University of California. Gardeners can check their soil temperatures using a soil thermometer to find out when they should apply the herbicide. Apply a herbicide that contains an active ingredient such as benefin or isoxaben, according to the University of California.

Post-Emergent Herbicide

• Post-emergent broadleaf killers effectively kill off existing weeds. Gardeners may use a broadleaf herbicide that contains atrazine on their St. Augustine lawn without harming their grass, according to the University of California. Furthermore, herbicides that contain either dicamba or 2,4-D are safe to use in your St. Augustinegrass. Avoid using a post-emergent selective herbicide if air temperatures exceed 85 degrees Fahrenheit, according to the University of Florida. Also, make sure you have at least two days of dry weather to allow the chemicals to absorb into the foliage.

Broad Spectrum Herbicide

• Broad-spectrum herbicides are commonly used to kill broadleaf weeds, but these herbicide types will also kill your St. Augustinegrass. Nonetheless, there is a way to use broad-spectrum herbicide without causing harm to your lawn. Spray a towel or rag with the herbicide. Wrap the towel or rag on the end of a rake. Touch the top of the broadleaf weeds growing above your St. Augustinegrass. Reapply in a few days if the weeds are still standing.