Of about 20 plants in the sedge family in eastern North America, the genus Cyperus contains the worst weeds. The two most notable of those are yellow (Cyperus esculentus) and purple (Cyperus rotundus) nutsedge.
The weeds we commonly call nut grass are the most common sedges encountered in the landscape. They're both herbaceous perennial plants that reproduce mainly from tubers.
Selective herbicides are products that kill targeted weeds but don't hurt the plants from which you're trying to remove the weeds.
Three of these chemicals can control yellow or purple nutsedge in the landscape. Unfortunately, none will effectively control them both.
- Pennant (metolachlor) controls yellow nutsedge when applied before the weeds emerge. The other two products work best when applied after the weeds start growing.
- Basagran T/O (bentazon) is best at controlling yellow nutsedge in certain ornamentals.
- Image (imazaquin) can control purple nutsedge in select ornamentals.
With no herbicide able to selectively control both sedges, it's important to apply the right chemical to the right sedge. So you have to be able to tell the difference between yellow and purple nutsedge.
When they're flowering, these plants are easy to distinguish. Many times, however, you'll find nutsedge plants that aren't flowering. Then you'll have to look at the leaves.
Besides having yellower flowers, yellow nutsedge has leaves with pinched tops. The leaf tips of the darker-flowered purple nutsedge are keeled (just like a boat).
Timing Important, Too
Applying a herbicide at the proper time is important for controlling sedges, too.
With preemergent herbicides, control will be poor if the product is applied after the plant is emerging. Pennant won't provide good control of yellow nutsedge after the leaves are out of the ground.
For the postemergent control of yellow and purple nutsedge, apply the proper herbicide after the foliage has emerged and the leaves are at least 4 to 6 inches long. This will provide adequate foliage so the plant can absorb the herbicide.
Apply Herbicides Properly
With Basagran T/O, herbicide symptoms should appear in three to five days. With Image, the weeds should begin showing the effects in 7 to 14 days. Follow label directions carefully for both products.
These products can be applied over the top in a few ornamentals. Basagran T/O, mixed 5 teaspoons to 1 gallon of water, treats 1,000 square feet of ajuga, English ivy, liriope, mugo pine and pachysandra.
Image DG, mixed a half-ounce to 3 gallons of water, can treat yucca, juniper species (see the label), liriope and pachysandra -- spray to wet the nutsedge leaves.
Two nonselective herbicides can also be used to control yellow and purple nutsedge. These products must be carefully directed to the weeds, since they can injure desirable plants, too.
- Manage (halosulfuron) is a relatively new postemergent product for controlling both yellow and purple nutsedge in turf. It can be used, too, to control yellow and purple nutsedge in established woody ornamentals.
- Roundup (glyphosate) can also control yellow and purple nutsedge, but must be used carefully.
You can also do other, nonchemical, things to help control nutsedges.
These plants aren't good at competing with other plants for light, space and nutrients. So it's important to use some type of mulch to cover bare soil. This will help reduce nutsedge infestations in ornamental beds.
Regular hand weeding and cultivating, if you can do it, can help reduce nutsedge populations, too.