PERENNIAL GRASS WEEDS AND THEIR CONTROL IN TURF

Agronomy Mimeo 73Revised February, 1999

INTRODUCTION

Those grasses that spread by above ground stems or runners (stolons) or below ground stems (rhizomes) include creeping bentgrass, roughstalk bluegrass, bermudagrass, quackgrass and nimblewill. Bermudagrass spreads rapidly by stolons and rhizomes. Creeping bentgrass, roughstalk bluegrass and nimblewill spread by stolons and seed. Quackgrass spreads by rhizomes and seed. Tall fescue, redtop, smooth paspalum, orchardgrass, and timothy spread by seed, and are called bunchgrasses because they generally do not produce either stolons or rhizomes. Bunchgrasses can be removed by digging, but stolon and rhizome spreading grasses are not effectively controlled in this manner. Furthermore, roto-tilling living plants that spread by stolons or rhizomes will actually encourage their spread.

Creeping bentgrass, bermudagrass and tall fescue are cultivated and considered desirable grasses in certain situations. Creeping bentgrass is used on golf course greens, fairways and tees in Maryland. Bermudagrass, especially the cultivars 'Tufcote', 'Midiron', and 'Vamont', are used as sports turfs in southern and lower Eastern Shore counties of Maryland. Tall fescue is used extensively for many situations ranging from home lawns to highway medians. Creeping bentgrass and bermudagrass are typically grown in monostands, and are not intentionally mixed with other species.

When tall fescue is mixed with predominantly Kentucky bluegrass stands (i.e., 50% Kentucky bluegrass) it will eventually develop a clumpy growth habit, which is considered objectionable by most people. Creeping bentgrass growing in Kentucky bluegrass, tall fescue or perennial ryegrass gives turf a patchy appearance. Bermudagrass, quackgrass, smooth paspalum and nimblewill are among the most objectionable of all perennial grass weeds. Bermudagrass, nimblewill, and smooth paspalum are warm-season grasses that develop a brown or dead appearance during their winter dormancy periods, which ranges from late October to late May in Maryland. Common bermudagrass grows very rapidly during summer and spreads into flower beds, gardens, patios, driveways, and sidewalks, as well as golf course fairways and putting greens. Quackgrass also spreads rapidly, and quackgrass, common bermudagrass and smooth paspalum produce coarse-textured and open (i.e. low density) stands. Smooth paspalum produces conspicuous clumps in all turfgrasses, but is most commonly found in golf course roughs. Orchardgrass also is a clumping bunchgrass that is a common contaminant in tall fescue seed, especially the cultivar 'Kentucky-31'. Timothy and redtop are less common in lawns, but they were used as components of highway seed mixes in the past. Roughstalk bluegrass seed is a serious contaminant of seed and is very difficult to control when it is accidently introduced in new seedings of Kentucky bluegrass lawns, and perennial ryegrass and creeping bentgrass grown on golf courses. Annual bluegrass is a prolific seed producer, but tends to be a short-lived weed in lawns, but can persist throughout wet summers. Conversely, annual bluegrass is a persistent weed when grown on intensively managed and well irrigated turf sites such as golf courses.

METHODS OF CONTROL

DIGGING

NON-SELECTIVE HERBICIDES

Glyphosate (trade names = Avail, Blot-out, Ortho's Kleen-up, Round-up Pro® and others) is the most commonly used non-selective systemic herbicide for grass control. Glufosinate (trade name = Finale®) also is systemic and it is effective against most perennial grass weeds that do not produce underground rhizomes. Rhizomatous grasses such as bermudagrass and quackgrass may not be effectively controlled by a single application of either glyphosate or glufosinate. Glyphosate and glufosinate should be applied only when soil is moist and weeds are growing vigorously. During warm weather, glyphosate will kill vegetation in 7 to 10 days. Glufosinate will kill foliage in about 3 to 5 days. Weeds that are under drought stress or have been hardened by cold temperatures are not effectively controlled by non-selective herbicides. The best times to spot treat clumps or patches of weed grasses with non-selective herbicides are fall and spring. After treated areas have turned brown, they may be tilled (if large) and seeded or sodded. Sodding is preferred in spring or summer because new seedings may be very slow in establishing, or they may fail to survive the heat, drought and disease stresses of summer. Glyphosate and glufosinate are immediately fixed to soil colloids and are rapidly degraded by microorganisms. Hence, treated areas may be disk-seeded within 24 hours of glyphosate or glufosinate treatment. However, it is best to wait at least 14 days before tilling or disk-seeding in order for non-selective herbicides to properly move into underground plant parts, and to determine if there have been spray skips. A spray application of glyphosate to stems or trunks of mature trees or shurbs with thick brown bark will not be injured.

Where bermudagrass and quackgrass are well established, two or more applications of glyphosate are recommended. Ideally, glyphosate-treated bermudagrass or quackgrass sites should be tilled after all leaves turn brown. These areas should be kept moist for 3 to 4 weeks and then re-treated if necessary with glyphosate to control any grass weeds that have survived. This procedure will help insure better control as rhizomes of many grass weeds often survive and begin re-growth about 3 weeks after the first glyphosate application. Even then, a very small number of bermudagrass and quackgrass rhizomes may survive a second glyphosate treatment, and a resurgence of the weed may recur in as little as one year following treatment. Therefore, it is very important to begin spot applications of glyphosate as soon as the first bermudagrass and quackgrass plants are observed. Spot treatment is best performed in late summer or early fall. Once large areas become infested with these rhizome forming perennials, they become extremely difficult to eliminate from a site.

SELECTIVE HERBICIDES

(1) chlorsulfuron (trade name = LESCO TFC) for control of tall fescue in mature (>1 year old) Kentucky bluegrass or for control of perennial ryegrass in mature creeping bentgrass;

(2) MSMA (trade name = Daconate 6, Weed-E-Rad and others) or DSMA (Methar 30, Weed-E-Rad 360 and others) for control of smooth paspalum or dallisgrass;

(3) fenoxaprop (trade name = Acclaim) for bermudagrass and roughstalk bluegrass suppression; and

(4) ethofumesate (trade name = Prograss) for suppression of bermudagrass and roughstalk bluegrass at spring green-up and in fall (prior to dormancy of bermudagrass).

Chlorsulfuron is for professional use only and it is sold in pre-measured blister packs. This herbicide will control tall fescue or perennial ryegrass when applied in a spot spray to clumps growing in Kentucky bluegrass lawns. This material is extremely phytotoxic to tall fescue and perennial ryegrass, and should not be used where these species are considered desirable. The contents of the blister pack are mixed with one or two gallons of water (see label as its use directions may vary) in a hand held sprayer. Each tall fescue clump is lightly sprayed to wet the leaf blades. Overspraying will injure or kill Kentucky bluegrass. To avoid overspraying, this herbicide should be mixed with a dye or each treated clump should be marked with a stake. Fall is the best time to use this herbicide although good control can be achieved with spring treatment. Tall fescue clumps will appear healthy for 3 to 4 weeks after treatment. Gradually, the clumps turn yellow and the tall fescue slowly dies over a 6 to 8 week period. Death of tall fescue is so slow that adjacent Kentucky bluegrass plants will fill-in and no dead spots will appear in the turf. Perennial ryegrass also dies out slowly, but not as slowly as tall fescue. Chlorsulfuron can be phytotoxic to sensitive ornamentals and it has a long soil persistence. If Kentucky bluegrass is oversprayed and killed the area can be disk-seeded successfully about 60 days after treatment. Seedlings, however, will appear stunted and will be slow to establish.

MSMA and DSMA can be used to control smooth paspalum and dallisgrass in turf. These herbicides must be applied in 3 applications on a 7 to 10 day interval. These treatments will discolor (yellow) turf for 4 to 6 weeks. Using a lot of water (i.e., 100 gallons per acre) will greatly reduce yellowing of the desired turfgrass. Applications should begin when the weed is actively growing, usually late June or early July in Maryland. Over application will cause significant injury to turfgrass. Treatments should be made when soil moisture is favorable to support vigorous weed growth and air temperature is in the range of 85 to 90 F.

Fenoxaprop is primarily used for postemergence control of annual grass weeds such as crabgrass and goosegrass (see Agronomy Mimeo 85 "Herbicides for Crabgrass and Goosegrass Control in Turf"). Fenoxaprop is phytotoxic to bermudagrass and roughstalk bluegrass and can be used to significantly reduce their growth and competitiveness. Successful bermudagrass and roughstalk bluegrass suppression is labor intensive. Fenoxaprop applications should begin at spring green-up of bermudagrass, which is around mid-May in Maryland. Fenoxaprop applied monthly from May to September will reduce bermudagrass colonization by over 90%. Re-growth of bermudagrass also will be greatly reduced the following spring. Multiple applications, however, may be required annually to keep bermudagrass growth in check. Suppression of roughstalk bluegrass with fenoxaprop is variable and should only be attempted in tolerant species such as Kentucky bluegrass, tall fescue, perennial ryegrass or zoysiagrass turfs. Fenoxaprop may cause some yellowing in Kentucky bluegrass and zoysiagrass, especially in spring under low mowing.

Ethofumesate is primarily used for postemergence control of annual bluegrass in perennial ryegrass, Kentucky bluegrass or tall fescue. Kentucky bluegrass and tall fescue, however, are less tolerant of ethofumesate than perennial ryegrass. It therefore should be used with more caution in Kentucky bluegrass and tall fescue. A single, spring application of ethofumesate at label use rates can severely damage bermudagrass. Spring use of ethofumesate, followed by summer applications of fenoxaprop, normally eradicates common bermudagrass. Ethofumesate, however, should not be applied to creeping bentgrass, fine-leaf fescue (i.e., creeping, Chewings, hard or blue sheep), zoysiagrass or other sensitive turfgrasses. Its use should be restricted to perennial ryegrass, tall fescue or Kentucky bluegrass.

For annual bluegrass control and roughstalk bluegrass suppression in perennial ryegrass, ethofumesate should be applied in mid-to-late fall. Ethofumesate is generally applied twice on a 21 day interval in the October to December time period. Spring applications provide erratic levels of annual bluegrass control. Total amounts of ethofumesate applied should not exceed 2.0 lb ai per acre for Kentucky bluegrass and tall fescue or 4.0 lb ai per acre for perennial ryegrass. Do not apply this herbicide at the aforementioned rates given to creeping bentgrass, or to actively growing bermudagrass or zoysiagrass. Dormant applications will delay the spring green-up of zoysiagrass and bermudagrass.

Perennial weed grasses are not controlled by broadleaf or preemergence crabgrass herbicides. Never use soil sterilants for weed control in turf. Of the herbicides discussed above, chlorsulfuron, ethofumesate and fenoxaprop are not available for homeowner use. Homeowners not familiar with using herbicides, however, should consider having perennial grass weeds controlled by professional applicators. These herbicides may be used safely if they are handled with extreme care. BE SURE TO FOLLOW ALL DIRECTIONS GIVEN ON HERBICIDE LABELS. Store all pesticides out of the reach of children and animals, and away from food and feeds. No endorsement of any herbicide listed is implied by the Maryland Extension Service. References to trade names does not constitute a guarantee or warranty. No discrimination is intended against products not mentioned.

Summary of selective and non-selective herbicides used to control or suppress perennial grass weeds.

Selective Herbicides	Grasses controlled or suppressed	Comments
Acclaim	bermudagrass roughstalk bluegrass	Multiple applications beginning early May suppress, but often fails to eliminate bermudagrass or roughstalk bluegrass
Daconate 6 or Methar 30	dallisgrass or smooth paspalum	Herbicide must be applied 2 to 3 times on a 7 to 10 interval. Use 100 gallons of water per acre to minimize injury to desirable turf
Lesco TFC	tall fescue perennial ryegrass	Clumps should be spot treated in fall or spring. TFC will injure or kill perennial ryegrass. For use in mature Kentucky bluegrass lawns or creeping bentgrass fairways. Do not apply to zoysiagrass.
Prograss	annual bluegrass bermudagrass roughstalk bluegrass	This herbicide is safe to apply to perennial ryegrass. High label rates will stunt and discolor Kentucky bluegrass and tall fescue, and can severely injure or discolor bentgrass, zoysiagrass, and bermudagrass

Non-selective Herbicides*	Grasses controlled or suppressed	Comments
Round-up	all grasses	Will kill or injure all grasses contacted. Two or more applications may be required to control bermudagrass or quackgrass.
Finale	all grasses	Will kill or injure all grasses contacted. May not effectively control rhizomatous grasses such as quackgrass and bermudagrass
Scythe	annual weeds	Scythe is mostly used for non-selective burn-down of foliage around trees, under fences, or adjacent to ornamental beds.
Reward	annual weeds	Reward is mostly used for non-selective burn-down of foliage around trees, under fences, or adjacent to ornamental beds. See label for annual bluegrass control in dormant bermudagrass and zoysiagrass.

* These are non-selective herbicides that will kill or severely injure desirable turfgrasses and other plants.

Mimeo prepared by Peter H. Dernoeden, Extension Turfgrass Specialist, Department of Agronomy