By: Chris Marble

Fig 1. Herbicide Damage

Glyphosate is the most widely used herbicide in landscape beds because it is effective on most weeds and is inexpensive. Although the US Environmental Protection Agency (E.P.A.) and other organizations have concluded that glyphosate is not likely to be carcinogenic, many homeowners, property managers, and other organizations have become fearful of glyphosate due to recent litigation. The topic of glyphosate safety is beyond the scope of this newsletter, but for those that are interested, the glyphosate risk-assessment material from the EPA’s review of glyphosate can be found online at https://www.epa.gov/ingredients-used-pesticide-products/draft-human-health-and-ecological-risk-assessments-glyphosate.

In cases where a customer prefers an alternative or in cases where glyphosate is not the best choice, it is important to know what other products are available for weed control in landscape planting beds. The most commonly used alternative to glyphosate in landscape beds is glufosinate (Finale). Glufosinate is a non-selective herbicide, so it has activity on most weeds. It is not translocated within the plant as well as glyphosate, however, so control of large or perennial species may not be as thorough as would be expected with glyphosate. However, this may provide an advantage in some cases because misapplication or drift from glufosinate is usually not as injurious as would be expected with glyphosate. Glufosinate is also much more expensive than glyphosate. Other non-selective herbicides that could be used include diquat (Reward), Scythe (pelargonic acid) and some organic products such as ammonium nonanoate (Axxe), and d-limonene (Avenger Ag). All of these options are contact herbicides – they will cause symptoms to develop rapidly but will likely offer poor control of large or perennial weed species.

Clopyralid (Lontrel) is a selective broadleaf herbicide that can be used over-the-top of certain landscape plants and as a directed application around others. It is effective on weeds such as black medic, dollarweed, horseweed (marestail), and many others. Clopyralid will not control any grasses or sedges and may not provide control of all broadleaf species in a particular landscape. For sedge control, bentazon (Basagran), sulfentrazone (Dismiss), imazaquin (Sceptor T/O), sulfosulfuron (Certainty), and halosulfuron (SedgeHammer, Prosedge) are available. These herbicides are most often used for sedge control but they will control certain broadleaf species as well. All of these products are also commonly used in most warm-season turfgrasses.

There are many options for controlling grassy weeds in landscape planting beds. Fenoxaprop (Acclaim Extra), fluazifop (Fusilade II), clethodim (Envoy) and sethoxydim (Segment) only control grassy weeds and can be applied over-the-top of labeled ornamentals. These grass herbicides (graminicides) differ in which grass species they are the most effective on as they each have different strengths and weaknesses, but all control a wide range of grassy weeds.

A more comprehensive list of postemergence herbicides labeled for use in and around ornamentals plants can be found at http://edis.ifas.ufl.edu/wg059. Other ways in which weed control can be improved in non-turf areas of landscapes including both chemical and non-chemical methods is available at http://edis.ifas.ufl.edu/ep523.

Another option is preventing the weeds from ever emerging by using preemergence herbicides. Most preemergence herbicides labeled for use in turfgrass can also be used in landscape planting beds. The 2017 Southeast Pest Management Guide (https://content.ces.ncsu.edu/southeastern-us-pest-control-guide-for-nursery-crops-and-landscape-plantings) contains a comprehensive list of all pre- and postemergence herbicides labeled for use in and around landscape plants.

North Carolina State University recently published a very useful glyphosate alternatives factsheet that discusses many of these herbicides in more depth as well as providing the signal word, required personal protection equipment, and organic labeling for each herbicide. That factsheet can be found at https://content.ces.ncsu.edu/are-there-alternatives-to-glyphosate-for-weed-control-in-landscapes.

Overall, there are other herbicide options in landscapes other than glyphosate. In many cases, glyphosate may not even be the best option or may be ineffective on certain weed species. For example, artilleryweed is a common nuisance in planting beds but glyphosate offers poor control. In other cases, contact herbicides, such as diquat or pelargonic acid, may be a better choice when applications have to be made in close proximity to ornamental shrubs. While other options are available, the disadvantage with these products is that they are usually not as broad-spectrum as glyphosate and often cost more. In all cases, using a combination of cultural practices, such as mulch application, along with labeled herbicide use will provide the best overall weed control.