Tim Murphy and Clint Waltz

Dept. of Crop and Soil Sciences, University of Georgia

 

Sulfonylurea (SU) herbicides are widely used for postemergence weed control in agronomic crops.  This chemical family has been extensively developed and is currently the most populous group of related herbicides due to the high selectivity of these herbicides to a wide range of plant species.   Selectivity is most often due to differential plant metabolism between species.  With small changes in molecular structure the speed of metabolism is altered and large differences in herbicide selectivity have been observed.   

The SU family of herbicides is now being rapidly introduced into the turfgrass market and sod producers now have more weed control options then ever before.  However, with the introduction of new herbicides can come a relatively steep learning curve.  For example, some SU’s control the various sedge species, others do not.  One SU, Revolver, provides excellent postemergence control of goosegrass, the others do not.  Most importantly, warm-season turfgrass tolerance can vary widely between seemingly similar herbicides.  For example, halosulfuron (Manage) can be safely applied for sedge control (Cyperus spp.) in both cool- and warm-season turfgrasses.  Conversely, trifloxysulfuron (Monument) adequately controls sedges, but is also used to control cool-season turfgrasses.  Therefore, the simple mistake of confusing two SU herbicides can have severe results.

Although sod producers have several new “tools” for chemical weed control, the speed at which these SU herbicides are coming to market can make it difficult to recall which herbicide is most useful for a given situation.   Therefore, our intention is to produce a quick reference to detail turfgrass tolerance (Table 1) and weed control (Table 2) for the sulfonylurea herbicides used in sod production.

Flazasulfuron (Katana) – (Registration Pending)

General:  Flazasulfuron is currently being developed by ISK Biosciences for the control of tall fescue, annual and perennial ryegrass, broadleaf weeds and sedges in bermudagrass and zoysiagrass.

Tolerant Turfgrasses:  Bermudagrass and zoysiagrass are tolerant to flazasulfuron.  Centipedegrass also possesses tolerance, but commonly shows growth regulation and off color after application.  Tall fescue, perennial ryegrass, Kentucky bluegrass and St. Augustinegrass are intolerant to flazasulfuron.

Overseeding Restriction: Perennial ryegrass can be overseeded into tolerant warm-season turfgrasses 2 to 12 weeks depending upon the application rate of flazasulfuron.

Use Pattern: If registered, flazasulfuron will be used for the control of sedges, certain broadleaf weeds, annual bluegrass and other weedy cool-season grasses, and as a spring transition aid in overseeded bermudagrass.

Application Rate: Flazasulfuron has undergone extensive testing in the field by universities at a wide range of rates.  Exact rates are not know at this time as this product is still in development, but will probably be in the 1.5 to 3.0 ozs./acre range.

Weeds Controlled:  Flazasulfuron provides near 100% control of annual and perennial ryegrass, tall fescue, white clover, common chickweed and numerous other broadleaf weeds.  Control of crabgrass with flazasulfuron has been observed to range between 50 to 95%, depending on weed size at time of application.  For best control, crabgrass must be between 1 to 2 inches in height.  Good control of various sedge spp. has also been noted.  The addition of MSMA and 2,4-D can improve control of sedges and dichondra, respectively   Since flazasulfuron is currently under the final stages of development and registration, it is not known which herbicides will be recommended for tank-mixing with flazasulfuron.

Foramsulfuron (Revolver)

General:  Control of weedy cool-season grasses and goosegrass in bermudagrass and ‘Meyer’ zoysiagrass.

Tolerant Turfgrasses:  Several bermudagrass cultivars (such as Tifway 419, Tifsport, Tifdwarf, Vamont, Common and others) and ‘Meyer’ zoysiagrass have shown good tolerance to foramsulfuron.   Centipedegrass and St. Augustinegrass are only moderately  tolerant to flazasulfuron.  All cool-season grasses, such as fescues, ryegrasses, bentgrasses, and bluegrasses are intolerant to this herbicide. 

Use Pattern:  Foramsulfuron will be used to control Poa spp., goosegrass, ryegrass and bentgrass in tolerant warm-season turfgrasses, including bermudagrass greens, This herbicide is also effective for the removal of “clump” fescue and “clump” ryegrass. Foramsulfuron is also labeled for use as a spring transition aid in overseeded bermudagrass.

Overseeding Restriction:  Ryegrass can be overseeded in treated areas two weeks after application.

Application:  Foramsulfuron is the first liquid SU, and is used at rates of 4.4 to 26.2 fl. oz/acre. Multiple applications may be required to control goosegrass or large volunteer ryegrass.  Herbicidal activity is greatest if rainfall or irrigation do not occur within 2 hours of treatment.  Foramsulfuron can be tracked and damage susceptible cool-season turfgrasses if spray droplets are not allowed to dry before traffic is permitted. Additionally, tracking can occur from morning dew the day after application.  Irrigation the morning after the previous day’s application will prevent tracking problems. Revolver should not be applied within 2 weeks of sprigging bermudagrass.

Weeds Controlled:  Foramsulfuron provides excellent control (>90%) of many troublesome cool-season grass species such as Poa annua, ryegrass, and clump fescue.  Additionally it is quite effective for the postemergence control of goosegrass.

Halosulfuron (Manage)

General: Control of yellow and purple nutsedge, and suppression of Kyllinga spp. 

Tolerant Turfgrasses:  All cool- and warm-season grasses are tolerant to halosulfuron applications.

Use Pattern:  Halosulfuron is used predominately for the control of sedges (Cyperus spp.).  Treatments are most effective when the sedge plants are between the 3 and 8 leaf stages.  Repeat applications, 6 to 10 weeks apart, are often required to control dense infestations.  However, no more than 4 applications (total of 5.33 oz/acre) can be made per acre per season. 

Halosulfuron may be applied to seeded, sprigged or sodded  turfgrasses that is well established.  However, sprigging, seeding, or sodding of turfgrasses should be delayed for 4 weeks after halosulfuron applications. 

Overseeding Restriction:  Overseeding with ryegrass may be conducted two weeks after application.  Bermudagrass can also be seeded two weeks after application.

Application Rate:  Halosulfuron is applied at 0.66 to 1.33 oz/acre.  A nonionic surfactant should be added at 0.25 or 0.5% v/v (1 to 2 qt. per 100 gal.).  Halosulfuron is rainfast after 3 hours, but best results have been observed when no rainfall or irrigation occurs within 4 hours of application.

Weeds Controlled.  Control of green kyllinga, yellow and purple nutsedge with halosulfuron can vary between 80 and 100%, depending on weed size and age at the time of application.  For this reason, repeat applications occurring 6 to 10 weeks after the initial application may be necessary to increase control.  Purple nutsedge is generally considered to be more sensitive to halosulfuron than yellow nutsedge.

Metsulfuron (Manor)

General Use: Control of ‘Pensacola’ bahiagrass, ryegrass, and numerous broadleaf weed species in turfgrass.

Tolerant Turfgrasses:  Kentucky bluegrass, fine fescue, bermudagrass, St. Augustinegrass, zoysiagrass and centipedegrass are labeled for metsulfuron applications.

Use Pattern:  Applications made to tolerant cool-season turfgrasses species when air temperatures are in excess of 85ºF may increase  injury.   Avoid applications of Manor to newly sprigged or sodded turfgrass.

Overseeding Restriction:  Winter overseeding must be postponed for 2 months after application.

Application Rate:  Metsulfuron is applied from 0.125 to 1 oz/acre in combination with a nonionic surfactant at 0.25% v/v (1qt per 100 gal).  For centipedegrass metsulfuron is used at rates of 0.25 to 0.5 oz/acre.  Chlorosis and stunting commonly occurs following application to centipedegrass. 

St. Augustinegrass, bermudagrass, and zoysiagrass can tolerate metsulfuron application rates up to 1 oz./acre.  Some chlorosis and stunting may occur after application and injury is worsened when the turfgrass is stressed from drought, cold temperatures, or poor fertility.  Metsulfuron is an excellent alternative to phenoxy herbicides for broadleaf weed control in St. Augustinegrass.

Weeds Controlled:  Metsulfuron will provide >90% control of overseeded perennial ryegrass, wild garlic, common chickweed, white clover, bristly mallow, annual lespedeza, spurges, dandelion, and numerous other broadleaf weeds.  To control ‘Pensacola” bahiagrass at levels > 80%, repeat applications at 4 to 6 week intervals are generally required.

Rimsulfuron (Tranxit)

General Use:  Control of annual bluegrass in overseeded and nonoverseeded warm-season turfgrasses and as a spring transition aid in overseeded bermudagrass.

Tolerant Turfgrasses:  Bermudagrass (fairway and putting green cultivars) and  zoysiagrass have good tolerance to rimsulfuron. Centipedegrass has moderate tolerance to rimsulfuron. St. Augustinegrass has a low to moderate level of tolerance to rimsulfuron.

Use Pattern: Slight yellowing and growth regulating effects have been observed for up to 7 days when rimsulfuron is applied to ‘Tifway’ bermudagrass.  Rimsulfuron is not recommended for use on newly sprigged or sodded bermudagrass.

Rimsulfuron is absorbed by both plant roots and foliage.  Therefore, irrigation 1 hour after application will move the herbicide into the soil and usually increase herbicidal effectiveness.  Relying on natural rainfall to incorporate the herbicide is unreliable.  When applying irrigation, care must be used to prevent surface runoff because rimsulfuron can move laterally with water in some situations.  Short, frequent, irrigations are most effective to incorporate rimsulfuron without producing runoff. 

Overseeding Restriction:  Overseeding should be delayed for 10 to 14 days after herbicide treatment.

Application Rate:  Rimsulfuron may be applied at 0.5 to 2 oz./acre with a nonionic surfactant at 0.25% v/v.  To remove perennial ryegrass from overseeded bermudagrass use 0.5 to 1 oz./acre.  Repeat applications, about 3 weeks apart, are commonly required for complete removal of Poa trivialis. 

Weeds Controlled:  Rimsulfuron provides >90% control of several grass species, including ryegrass, fescue, and Poa annua, and broadleaf species such as common chickweed and spotted spurge. 

 

Sulfosulfuron (Certainty)

General: Sulfosulfuron is the newest SU herbicide and has been registered for the control of sedges, Poa annua, tall fescue, henbit, common chickweed and other broadleaf weeds in warm-season turfgrasses.

Tolerant Turfgrasses:  Sulfosulfuron is recommended for use on bermudagrass, zoysiagrass, centipedegrass and St. Augustinegrass.  

Overseeding Restriction: Ryegrass can be overseeded in treated areas 7 to 10 days after application.

 

Use Pattern:  Sulfosulfuron has demonstrated excellent control of various members of the sedge family when applied during the summer months. 

Application Rate: Sulfosulfuron is used at rates of 0.75 to 2.0 ozs./acre. has shown excellent control of sedges and tall fescue. 

Weeds Controlled:  In turfgrasses, sulfosulfuron has shown excellent activity for sedge spp., tall fescue and certain annual broadleaf weeds.  This herbicide is also being evaluated for Poa trivialis removal in creeping bentgrass fairways.

Trifloxysulfuron (Monument)

General Use: Trifloxysulfuron will be used for broadleaf weed, sedge, annual bluegrass and tall fescue control in bermudagrass and zoysiagrass.

Tolerant Turfgrasses:  Bermudagrass and zoysiagrass are tolerant to trifloxysulfuron.  However, a reduction in leaf elongation and suppression of seedheads has been observed in bermudagrass and zoysiagrass species.  Tall fescue, centipedegrass and St. Augustinegrass are not tolerant to Monument.

Overseeding Restriction:  Overseeding with cool-season turfgrasses should be delayed for 6 weeks after herbicide application. 

Use Pattern:  Trifloxysulfuron should not be applied to newly established turfgrasses until 100% ground cover, and a 2 inch root depth is achieved. 

Trifloxysulfuron may be applied to control Poa annua and sedges, or as a transition aid for removing overseeded ryegrass.  Bermudagrass and zoysiagrass can be sprigged or seeded 4 weeks after herbicide application.

Application Rate:  Trifloxysulfuron may be applied between 0.1 and 0.56 oz/acre with 0.25 or 0.5% v/v nonionic surfactant.  Application rates between 0.1 and 0.3 oz/acre are used when removing overseeded ryegrass and Poa trivialis; the lower use rate allows for slower transition.  A slight delay in bermudagrass green-up has been observed when applications were made during dormancy.  For Poa annua and sedge control, the 0.3 to 0.56 oz/acre application rates are recommended. 

Repeat applications are often needed, 4 to 6 weeks after application, for control of particularly troublesome weeds such as sedges and tall fescue.  However, a total of 1.7 oz/acre should not be exceeded within 1 year.  Trifloxysulfuron is rainfast within 3 hours of application.

Weeds Controlled:  Greater than 90% control has been observed of ryegrass, fescue, corn speedwell, Virginia buttonweed and sedges. Repeat applications after 4 to 6 weeks may be necessary depending on environmental conditions and weed size at time of application.  Trifloxysulfuron will also provide some suppression of crabgrass, dallisgrass and bahiagrass.  MSMA may be added to trifloxysulfuron in order to improve control of these particular grasses.

Summary

Sulfonylurea herbicides are highly useful herbicides in turfgrasses.  Although no single herbicide has been developed to control all troublesome weeds such as sedges, Poa annua, “clump” tall fescue and “clump” perennial ryegrass, proper selection of the appropriate SU herbicide will enable sod producers an effective way to control these weeds.  Research is continuing to identify weeds controlled by SU herbicides. Additional research is also needed to determine the tolerance of turfgrass species at various growth stages in sod production systems. Many SU herbicides can be used as a spring transition aid to remove perennial ryegrass and Poa trivialis from bermudagrass overseeded the previous fall. The SU herbicides offer sod producers solutions to many difficult weed management problems, and rotational alternatives to presently used herbicides.  However, a word of caution is needed.  All of the SU herbicides have the same mode-of-action, i.e. they inhibit the ALS enzyme (acetolactate synthase) which is involved in the production of three essential amino acids.  Certain weed species have naturally-occurring biotypes that are resistant to ALS-inhibiting herbicides such as the sulfonylurea ureas.   Continued use of SU herbicides over a period of years, and in the absence of rotation to herbicides with a different mode-of-action, can lead to the development of SU-resistant weeds.  This has occurred in agronomic crops, and in roadside turfgrasses, where SU herbicides were not used properly used. SUs are highly useful and effective herbicides.  But, it will be imperative to rotate SU herbicides with other herbicides to prevent the development of SU-resistant weeds.  This is highly effective and exciting herbicide family, but, don’t forget a basic principle of pest management, i.e. rotate the use of herbicides with different modes-of-action to prevent the buildup of herbicide-resistant weed populations.  If this basic principle is followed, sod producers will have highly effective, postemergence herbicides to control numerous, problem weeds in turfgrasses for many years to come. 

Table 1.  Tolerance of warm- and cool-season grasses to sulfonylurea herbicides.

 

	St. Augustinegrass	Bermudagrass	Centipedegrass	Zoysiagrass	Perennial Ryegrass	Tall Fescue
Chlorsulfuron	I	T	I	I	S	S1
Flazasulfuron	S-I	T2	I-T	T	S	S
Foramsulfuron	I	T	S	T	S	S
Halosulfuron	T	T	T	T	T	T
Metsulfuron	T	T	T	T	S	S
Rimsulfuron	S-I	T	I	I-T	S	S
Sulfosulfuron	T	T	T	I-T	I	S
Trifloxysulfuron	S	T	S	T	S	S

T=tolerant, I=intermediate tolerance, S=sensitive

¹Fine Fescue is tolerant to chlorsulfuron applications.

² Many bermudagrasses have high tolerance to flazasulfuron, but ‘Floradwarf’ has shown low to moderate tolerance.

 

Table 2.  Weed control for sulfonylurea herbicides.

 

	chlorsulfuron	flazasulfuron	foramsulfuron	halosulfuron	metsulfuron	rimsulfuron	sulfosulfuron	trifloxysulfuron
	%
Grass Weeds
bluegrass, annual	P	G-P	E	P	P	E	F-G	E
crabgrass spp.	P	F-E	P	P	P	P		F
fescue, clump	E-G	E	E	P	F-P	E		E
goosegrass		P	G	P	P	P	P	P
ryegrass, clump		E	E	P	E	E	P	E
ryegrass, Italian	E	E	E	P	E-G	E		E
Broadleaf Weeds
buttonweed, Va.	F	F		P	F			F-E
chickweed, common	G	E		P	E	E-G
clover, white	F	E		P	E
corn speedwell		P	E	P	G	P	P	E
dandelion	G-F	E-G			E			E-G
dichondra		P		P	E			E-G
henbit	G	E	G-F	G-F	E	G-F	G-F	G-F
knotweed, prostrate	G-E	F	P	P	G-E	P	P	P
mallow	F			P
plantain spp.	G-F