Sedges simply have few endearing qualities and people don’t like them, unless you count the horticulturalist who favors ornamental sedges or those turkey hunters who plant “Chuffa” (actually yellow nutsedge, Cyperus esculentus) for their game.   Sedges typically achieve fame by holding prominent places among the worlds most troublesome weed species.  

In Virginia, we deal with a wide range of sedges but not quite as many species as folks contend with, say, in Florida.   Our most common sedges in home lawns in order of abundance include yellow nutsedge, annual sedge (Cyperus compressus), purple nutsedge (C. rotundus), false green kyllinga (Kyllinga gracillima), green kyllinga (Kyllinga brevifolia), and fragrant kyllinga (Kyllinga sesquiflorus).   Hundreds of other sedge species occur in the state but are often relegated to marsh land, ditch banks, and the occasional home lawn.   Historically, few herbicides have been available for sedge control in lawns but that trend is changing.   Three new herbicides have been registered for sedge control in the last few years.

THE BASICS OF TURF WEED CONTROL

The golden rule of turfgrass weed control is this:   “The majority of turf weeds are controlled by good cultural practices, such as cultivar selection, fertility, and mowing, that promote a healthy turfgrass canopy.”   You must be able to grow grass; not just kill weeds.   In addition, your ability to diagnose chronic problems in the environment that limit turfgrass growth is paramount to achieving long-term weed control solutions.   The first step of a weed control program is often labeled “identify the weed.”   This first step is sufficient for many situations but not for turfgrass.   The first step in a turfgrass weed control program is “identify the problem that has limited turfgrass competitiveness and fix it.”   If the underlying problem that has allowed weeds an opportunity for invasion is not fixed, new weeds will simply invade the area after the current weeds are controlled.   Be aware that some environments are not suited to turfgrass and weed problems will persist in those areas.  

CULTURAL PRACTICES TO LIMIT SEDGES

Sedges proliferate in wet environments but may grow in dry, well-drained spots if competition is limited.   Most perennial sedges produce seed and underground tubers.   The larger a population gets the more seed and tubers plants make.   Tubers may lie in wait for years before sprouting so it is unlikely that you will eradicate your sedge problem in just a few years.   The goal is to get your sedge infestation to the level that a few spot treatments per year will keep the problem under wraps.   Anything you can do to improve your turfgrass canopy density and competitiveness will help exclude sedge invasion.   The best ways to limit sedge establishment in your lawn include:

• Avoid excessive irrigation
• Aerify and improve drainage
• Treat small infestations before they expand

By keeping the lawn “happy” and controlling soil moisture levels, you will achieve most of your long-term sedge control before any herbicide has been applied.

HERBICIDE OPTIONS

Preemergence Herbicides.   The foundation of turfgrass weed control in the lawn is preemergence herbicides for crabgrass control.   The most common preemergence herbicides for crabgrass control will contain at least one of the following ingredients:   benefin, bensulide, dithiopyr, pendimethalin, prodiamine, oryzalin, oxadiazon, siduron, and trifluralin.   Out of all these chemicals, only oxadiazon (Ronstar™) has activity on emerging sedges because it is absorbed through shoots and not roots.   However, preemergence herbicides can not shoulder the sedge control burden alone.   Most sedge problems are tackled with postemergence herbicides.  

Postemergence Herbicides.   Common sense will tell you that large sedges are more difficult to control with postemergence herbicides than small, young plants.   The difficulty of sedge control increases with the following factors:

• Large plants at treatment time
• Dense population with increased nutlet and seed reserves in soil
• Daily irrigation or above average rainfall

Large plants often survive the treatment and sprout anew.   Increased nutlet and seed reserves will increase the duration of sedge emergence, making it impossible to kill all plants in a single treatment.   Rainfall or irrigation provides the continuous stimulus that nutlets or seed need to emerge.

Both contact and systemic herbicides are available for sedge control.   Contact herbicides only kill tissue where the droplet lands and require excellent spray coverage and young weeds to be effective.   MSMA and bentazon (Basagran™, Lescogran™) are examples of contact herbicides.   Systemic herbicides are distributed throughout the plant upon entry.   Halosulfuron (Manage™, Sedgehammer™) and (trifloxysulfuron, Monument™) are examples of systemic herbicides.   It is actually better to apply less spray to a given area and insure that spray solutions are more concentrated in each spray droplet when dealing with systemic herbicides.   Systemic chemicals must move into the plant and across plant membranes for full effectiveness.   This movement usually depends on a concentration gradient of high herbicide concentration in the droplets that land on the leaf surface and low concentration of herbicide in the plant.   When you dilute the herbicide to spray more fluid per unit area, you end up with several diluted droplets that land all over the plant but result in less herbicide moving into the plant.   So, the strategy is to apply about two gallons per thousand square feet with contact-type herbicides and half to one gallon per thousand square feet with systemic herbicides.

Sedges can be treated any time from emergence until frost.   Keep in mind that plants will continue to emerge after you have treated but you can’t let emerged plants get too big.   Thus, you will probably need to treat at least twice to control sedges throughout the season.   Table 1 shows several products that are currently available for sedge control.   It is impossible to cover every possible product for sedge control in a single article and mention of a particular product was not meant to exclude other suitable products that may be used for the same purpose.   These herbicides are tabulated for reference only and you should always read and follow chemical label instructions when using any pesticide.   More information on sedge identification and control is available at Dr. Askew’s web site, www.turfweeds.net.

Dr. Shawn Askew is an assistant professor and extension turfgrass weed scientist at Virginia Polytechnic Institute and State University ( Blacksburg, VA).