Revised February, 1996
INTRODUCTION
Spring and summer germinating annual grasses such as crabgrass
(Digitaria spp.) and goosegrass (Eleusine indica) are among the most
common and troublesome weeds in Maryland. Crabgrass seed normally
begin germinating after March 15 in Southern and Eastern Shore
Maryland, after April 1 in the Baltimore-Washington D.C. corridor,
and in late April in western counties. Goosegrass seed generally
begin germinating after May 15 in central Maryland. Most of the
crabgrass seed germinate by early July, but large numbers of
goosegrass seed will continue to germinate throughout summer. As the
plants mature, seedheads are produced and mature seed fall to the
ground providing next year's crop of crabgrass and goosegrass.
Crabgrass and goosegrass plants are then killed by early frosts in
the fall.
CULTURAL CONTROL
Growing a healthy, dense and
vigorous turf is one of the best methods of keeping crabgrass and
goosegrass out of turf. A vigorous, thick turf shades the weed seed
and greatly reduces germination. In thin, weak turf, crabgrass is one
of the first weeds to invade. Although it is not always easy to grow
turf in Maryland, there are several management practices that, when
followed, will help to reduce weed encroachment. The following six
steps can lead to healthy, dense and vigorous turf, which will resist
weed invasion:
1. Plant high quality seed of recommended cultivars.
2. Plant seed of cool-season grasses between late August and early October. Avoid spring or summer seedings.
3. Fertilize cool-season turfgrass in fall with mostly slow release (>50%) nitrogen fertilizers. Apply phosphorus and potassium at least one time per year.
4. Reduce soil acidity with lime as recommended by a soil test.
5. Mow lawns at the recommended height (2.5 to 3.5 inches for Kentucky bluegrass, perennial ryegrass and fescues).
6. When irrigating, apply water when turf begins to wilt (i.e. turf develops a blue-gray color and "footprinting" occurs). Water deeply by wetting the soil to a 4- to 6-inch depth. Frequent, light watering greatly encourages crabgrass and goosegrass encroachment, discourages deeper rooting, and lowers the environmental stress tolerance of turfgrasses.
Crabgrass and goosegrass can be controlled with herbicides. There are two types of herbicide applications. The first type, "PREEMERGENCE", prevents crabgrass, goosegrass, foxtail and many other seeds from emerging. The second type, "POSTEMERGENCE", kills emerged and actively growing plants.
PREEMERGENCE HERBICIDES
Preemergence herbicides are
generally more effective and easier to apply than postemergence
herbicides, but they must be applied in the spring before annual
grass weed seed germinate. Preemergence herbicides should first be
applied in mid-March to early April to be effective. Most herbicides
should be reapplied 6 to 8 weeks later for more consistent,
season-long control. The rates (in pounds of active ingredient to be
applied per acre, or lb ai/A) of those herbicides that should be
applied twice are given a designation such as 1.5 + 1.5 lb ai/acre.
This means that the first application should be applied at 1.5 lb
ai/acre and the second (6 to 8 weeks later) at 1.5 lb ai/acre. If
goosegrass, but not crabgrass, is a problem, the preemergence
herbicide application may be delayed until early May. The
descriptions of commercially available preemergence herbicides for
annual grass control in turfgrass are as follows:
Benefin
Trade Name: Balan
Chemical Name: N-butyl-M-ethyl-a,a-trifluoro-2,6-dinitro-p toluidine
Formulations: Granular, dry flowable or combinations with fertilizer
Comments: Benefin is safe to use on established Kentucky bluegrass, tall fescue, perennial ryegrass, bentgrass, bermudagrass or zoysiagrass. Benefin should not be used on fine fescues, on newly seeded turf or on newly sprigged bermudagrass and zoysiagrass. Reseeding should be delayed at least 6 weeks after application of benefin. Two applications of benefin (2 + 2 lb ai/acre), 6 to 8 weeks apart, are needed for season-long control of crabgrass and goosegrass in Maryland.
Benefin + Trifluralin
Trade Name: Team
Chemical Name: Benefin (see above) + a,a,a-trifluoro-2,6-dinitro-N N-dipropyl-P-toluidine
Formulations: Granular or in combination with fertilizer
Comments: Team is safe to use on all cool-season grasses (such as Kentucky bluegrass, perennial ryegrass, and the fescues), except bentgrass turf. Team has been reported to injure Kentucky bluegrass in some regions of the U.S. Team also may be safely applied to mature bermudagrass and zoysiagrass. Use Team on established turfs only, do not apply to seedling grasses. Reseeding should be delayed at least 6 weeks after application. Two applications of Team (1.5 + 1.5 lb ai/acre), 6 to 8 weeks apart, are needed for season-long control of crabgrass and goosegrass in Maryland.
Bensulide
Trade Name: Betamec, Betasan, Lescosan, Pre-San, and others
Chemical Name: S-(0,0-diisopropyl phosphorodithioate) ester of N (2-mercaptoethyl) benzenesulfonamide
Formulations: Granular, liquid or in combinations with fertilizer
Comments: Bensulide is safe to use on established creeping bentgrass, Kentucky bluegrass, tall fescue, fine fescue, perennial ryegrass, bermudagrass or zoysiagrass. Bensulide should not be used on newly seeded turf or on newly sprigged bermudagrass and zoysiagrass. Reseeding should be delayed at least 4 months after application of bensulide. One application per season (7.5 to 12 lb ai/acre) provides erratic levels of crabgrass control. Bensulide generally provides a poor to fair (<70%) level of goosegrass control.
DCPA
Trade Name: Dacthal and others
Chemical Name: Dimethyl tetrachloroterephthalate
Formulations: Granular, flowable, or combinations with fertilizer
Comments: DCPA is safe to use on established Kentucky bluegrass, tall fescue, perennial ryegrass, bermudagrass or zoysiagrass. DCPA should not be used on fine fescues or newly sprigged bermudagrass or zoysiagrass. DCPA can be used on seedling turf after the first mowing, but not during the establishment period. Reseeding should be delayed at least 60 days after application of DCPA. DCPA will also control spotted or prostrate spurge from seed. Two applications of DCPA (10.5 + 5 lb ai/acre), 6 to 8 weeks apart, are usually needed for season-long crabgrass control. DCPA will not control goosegrass effectively.
Dithiopyr
Trade Name: Dimension
Chemical Name: 3,5-pyridinedicarbothioic acid, 2-(difluoromethyl) 4-(2-methylpropyl) -6-trifluoromethyl)-S,S-dimethyl ester
Formulations: Liquid (emulsifiable concentrate), granular and fertilizer combinations
Comments: Dithiopyr is safe to apply to most turfgrasses including: creeping bentgrass (spring, preemergence use only), Kentucky bluegrass, tall fescue, creeping red fescue, perennial ryegrass, bermudagrass and zoysiagrass. Granular forms of dithiopyr effectively controls crabgrass, goosegrass and foxtails preemergence with a single spring application of 0.38 lb ai/acre. The emulsifable formulation (1EC) of dithiopyr provides more consistent control when applied twice per season (0.25 + 0.25 lb ai/A). Dithiopyr also provides effective postemergence control of crabgrass. For postemergence control, dithiopyr should be applied to 1- to 4-leaf stage crabgrass at 0.25 to 0.38 lb ai/acre for granular formulations and at 0.5 lb ai/acre for the emulsifiable concentrate. Tillered crabgrass will not be effectively controlled, therefore dithiopyr 1EC (0.38 lb ai/acre) should be tank-mixed with either Acclaim (0.09 lb ai/acre) or MSMA (1.0 lb ai/acre) and applied prior to mid-June. After 1 July use either Acclaim, MSMA or DSMA alone. Reseeding should be delayed for 3 months following use.
Oxadiazon
Trade Name: Chipco Ronstar G
Chemical Name: 2-tert-butyl-4(2,4-dichloro-5-isopropoxypheny)1 2-1,3,4-oxadiazolin-5-one
Formulations: Granular and wettable powder
Comments: Oxadiazon is safe to use on established Kentucky bluegrass, tall fescue, perennial ryegrass, bermudagrass and zoysiagrass. Oxadiazon should not be used on newly seeded turf or fine fescues, but it can be used over newly sprigged bermudagrass or zoysiagrass. Reseeding should be delayed at least 4 months after application of oxadiazon. One spring application of oxadiazon (4 lb ai/acre) will give season-long control of annual grasses. If crabgrass is not a problem, one application (3 lb ai/acre) around May 1 will give excellent goosegrass control. Oxadiazon is one of the most effective preemergence herbicides available for control of goosegrass in turf. Only use the granular form on cool season turf.
Pendimethalin
Trade Name: Lesco Pre-M; various O.M. Scott labels (such as Turf Weedgrass Control, Weedgrass Control 60 WDG, and others); Pendimethalin
Chemical Name: N-(1-ethylpropyl)-3-4-dimethyl-2,6 dinitrobenzenamine
Formulations: Granular, water dispersable granule (WDG) or in combination with fertilizer
Comments: Pendimethalin is safe to use on established stands of Kentucky bluegrass, perennial ryegrass, tall fescue, fine fescue, bermudagrass and zoysiagrass. Do not use on bentgrass or where annual bluegrass is the desired species. On new seedings, wait until grass has been mowed at least 4 times and has filled-in. Reseeding should be delayed 16 weeks after application. Pendimethalin will provide some preemergence control of oxalis, spurge and other broadleaf weeds. Two applications of pendimethalin (1.5 + 1.5 lb ai/acre), 6 to 8 weeks apart, is recommended for season-long control of crabgrass and goosegrass in Maryland.
Prodiamine
Trade Name: Barricade
Chemical Name: N3,N3-di-n-propyl-2,4-dinitro-6-(trifluoromethyl) M-phenylenediamine
Formulations: Water dispersable granule or in combination with fertilizer
Comments: Prodiamine is safe to use on Kentucky bluegrass, perennial ryegrass, tall fescue, bermudagrass and zoysiagrass. Use on mature turf only and do not apply to putting greens. Prodiamine effectively controls crabgrass, goosegrass and foxtails with a single spring application of 0.50 to 0.65 lb ai/acre of the 65WDG formulation. The higher rate is suggested where goosegrass or chronic high levels of crabgrass occur. In general, higher rates (i.e., ³0.75 lb ai/A) of prodiamine are suggested when using granular formulations. Reseeding should be delayed 16 weeks after application.
Siduron
Trade Name: Tupersan and others
Chemical Name: 1-(2-methylcyclohexyl)-3-phenylurea
Formulations: Wettable powder, granular or in combination with fertilizer
Comments: Siduron is safe to use on established and newly seeded Kentucky bluegrass, tall and fine fescues, perennial ryegrass and some cultivars of bentgrass and zoysiagrass. Siduron should not be used on certain bentgrass cultivars, on bermudagrass or on golf course putting greens. Following label recommendations, siduron can be safely used at the time of or immediately following seeding of tolerant grasses. Two or more applications of siduron, 3 to 5 weeks apart are necessary if satisfactory annual grass control is to be achieved in seedling turf. See the label for proper use rates on seedling turf. Siduron, however, would require multiple applications to provide effective season-long crabgrass control in Maryland. Siduron is not likely to control goosegrass.
Except as otherwise noted, most of these herbicides provide good to excellent season-long crabgrass control when used properly. Precautions that will help assure good control are as follows:
1.Use the rate recommended on the label-no more, no less.
2.Avoid skips and overdoses. Insure good, uniform coverage by applying half the recommended rate in two directions (at right angle to each other).
3.Apply at least 1 to 2 weeks before weeds germinate, which is generally late March or early April for most regions in Maryland. Late April would be acceptable in Allegany and Garrett counties.
4.Water-in immediately and thoroughly after chemicals are applied.
5.Do not disturb the soil surface (by aerifying, spiking, or verticutting) after chemicals have been applied until fall.
NOTE: The actual chemical name of each herbicide that must appear on the container was listed above. Take this Agronomy Mimeo with you when shopping and compare names to be sure you are buying the chemical you desire. Preemergence herbicides usually provide the easiest and perhaps most economical approach to summer annual grass weed control.
POSTEMERGENCE HERBICIDES
Postemergence herbicides are used to
kill weeds after they germinate and emerge from the soil. Crabgrass
and goosegrass are easiest to control with postemergence herbicides
when they are small, and in the 2- to 4 leaf stage of growth. This
normally occurs in late June or early July in most areas of Maryland.
The most common postemergence herbicides used for annual grass
control in turf are organic arsenicals, dithiopyr (early
postemergence only), fenoxaprop, and quinclorac (pending EPA
registration). Only fenoxaprop effectively control goosegrass.
The organic arsenical forms of postemergence herbicides are safer to use and are less poisonous to animals and humans than the inorganic arsenical forms. The inorganic forms are no longer produced, but available stocks are legal to use in Maryland on golf courses only. Available postemergence annual grass weed herbicides are listed and discussed below:
Chemical Names of Organic Arsenicals:
AMA: Ammonium methanearsonate
DSMA: Disodium methanearsonate
MAMA: Monoammonium methanearsonate
MSMA: Monosodium methanearsonate
Trade Names: Methar 30, Weedone Crabgrass Killer, Ortho Crabgrass and Dandelion Killer, Super Methar, Daconate 6, DSMA and others.
Formulations: Granular and liquid-alone or in combination with other herbicides
Comments: These postemergence herbicides are most effective when applied to seedling crabgrass or foxtail plants. The organic arsenicals are not generally effective in controlling goosegrass. Generally, two and sometimes more treatments are needed, and they should be made on 7- to 10-day intervals. Soil should be moist before treatments are made. Desirable turfgrasses are temporarily discolored after treatment, especially if they are under stress from heat or drought. Spray formulations are more effective than granular forms. Follow directions on the container for rates to apply. Do not irrigate for 24 hours after they are applied and do not apply if rain is forecast within 24 hours of the day you intend to apply the herbicide.
Dithiopyr
Comments: Use of dithiopyr and other relevant information about this chemical is outlined above in the section on preemergence herbicides. Dithiopyr only provides early (i.e. 1 to 4 leaf stage) postemergence control of crabgrass. Little information exists regarding its ability to postemergently control other annual grasses and therefore dithiopyr is currently labelled only for postemergence crabgrass control. Dithiopyr should not be used on creeping bentgrass as a postemergence herbicide, but it is safe to apply postemergently to most other turfgrass species. Its use after early June is generally not recommended in Maryland.
Fenoxaprop
Trade Name: Acclaim
Chemical Name: (±)-ethyl 2-[4-[(6 chloro 2-benzoxaolyl) oxy]phenoxy]propanoate
Formulations: Sprayable (emulsifiable concentrate)
Comments: Controls crabgrass, goosegrass, foxtail and fall panicum. May stunt or discolor Kentucky bluegrass if applied prior to July. Safe to use on perennial ryegrass, tall fescue, fine fescues, and zoysiagrass. Acclaim may yellow low cut turfs such as those grown on fairways and tees. Do not apply to bermudagrass, and refer to label regarding low rate usage on bentgrass. Acclaim is relatively safe (may cause yellowing) to apply to tall fescue and perennial ryegrass seedlings, but it may severely injure seedling Kentucky bluegrass less than one year old. Apply when crabgrass is just above the turf canopy (usually early July), but prior to the time when weeds have developed 4 or more tillers. There must be good soil moisture and actively growing weeds for Acclaim to be effective in a single application.
Due to antagonism within the weed (i.e., not the spray tank), Acclaim should not be tank mixed with a broadleaf weed herbicide or be applied within 14 days following a broadleaf weed herbicide application. A broadleaf weed herbicide may be applied 24 hours after Acclaim without diminishing the ability of Acclaim to control annual grass weeds. Do not mow treated turf within 24 hours of application. Acclaim is more effective when applied through flat fan nozzles. Effectiveness may be reduced by nozzles, such as flood jet nozzles, that produce large droplet sizes. The recommended rate of Acclaim will vary (0.12 to 0.35 lb ai/acre) with weed size, vigor and other factors noted on the label. Multiple applications are generally needed for goosegrass control because this weed germinates throughout the summer and fenoxaprop alone has no preemergence activity.
Quinclorac
Trade Name: Drive : Pending EPA Registration = May be available under an experimental use permit (EUP).
Chemical Name: 3,7-dichloro-8-quinolinecarboxylic acid
Formulations: Wettable powder and dry flowable
Comments: Quinclorac effectively controls (at 0.38 to 1.0 lb ai/acre) crabgrass and barnyardgrass, but not goosegrass. It can provide about 30 days of preemergence crabgrass control. It is safe to apply to Kentucky bluegrass, perennial ryegrass, bermudagrass and zoysiagrass. It may cause a slight yellowing in tall fescue, but can be extremely phytotoxic to creeping red fescue and bentgrass maintained on putting greens. It causes yellowing in fairway creeping bentgrass, which can persist for 20 to 30 days. Quinclorac effectively controls young crabgrass as well as mature, multi-tillered plants. It also effectively controls clovers, violets and most speedwells. It is weak or ineffective against dandelion, plantains, oxalis and other broadleaf weeds.
A weed control program must be accompanied by a good turf management program. When weeds are removed, large bare areas should be sodded or re-seeded in the fall as these open spaces will be invaded by new weeds. Proper fertilization, irrigation and mowing greatly reduce and often eliminate significant crabgrass or goosegrass problems in turf.
C A U T I O N:
Herbicides can be poisonous, but they may be used safely if you HANDLE THEM WITH CARE. Use only the recommended rates. Follow directions and precautions on the label. Store all pesticides out of reach of children and animals and away from feed, seed and foodstuffs. References to trade names do not constitute an endorsement or warranty by the University of Maryland. No discrimination is intended against products not mentioned.
Mimeo prepared by: Peter H. Dernoeden, Extension Turf Specialist, Department of Agronomy