Tall Fescue Online Monograph

Weeds

Identification. Weeds of tall fescue turfs are categorized as broadleaves, grasses, or sedges (Carex and Cyperus spp.). Broadleaf weeds are easier to identify than grassy weeds and sedges. Most broadleaf weeds have wide leaves that are produced in pairs or multiples. Leaves are often suspended above the main stem by a petiole, and leaf veins form a net-like pattern. A leaf may be simple, with only one leaflet (e.g., dandelion) or compound, with multiple leaflets (e.g., white clover). Grassy weeds such as annual bluegrass (Poa annua L.), large crabgrass, and dallisgrass (Paspalum dilatatum Poir.) have an appearance and growth habit resembling those of tall fescue. Although stems of grassy weeds may be round or flat, leaves are often blade-like with veins running parallel from base to tip. Unlike grassy weeds, sedges have leaves arranged in three vertical rows and a triangular stem.

Life Cycle. Knowing the life cycle of a particular weed species is helpful when developing an effective management strategy. Turfgrass weeds may be annuals, biennials, or perennials. Annual grassy weeds often are further subdivided into one of two categories, summer annuals (e.g., goosegrass) or winter annuals (e.g., cheatgrass, Bromus tectorum L.). Temperatures in the upper 1.3 cm (0.5 in) of soil at which summer annual weed seeds often germinate are as follows: crabgrasses, 13°C (55°F); barnyardgrass and goosegrass, 16°C (60°F); and yellow and green foxtails, 18°C (65°F) (Watschke et al., 1995). Such information is important when scheduling the application of a preemergence herbicide treatment.

Preemergence Herbicides. Several preemergence herbicides effectively control many species of annual grasses in tall fescue when applied before weed seed germination (Nutt and Murphy, 2004; Johnson and Carrow, 1995) {e.g., benefin (N-butyl-N-ethyl-a,a,a -trifluoro-2,6-dinitro-p-toluidine; Balan, Dow), benefin + oryzalin (3,5-dinitro-N⁴,N⁴-dipropylsulfanilamide; Balan XL, Dow); bensulide (O,O-diisopropyl S-2-phenylsulfonylaminoethyl phosphorodithioate; Bensumec, PBI Gordon; Betasan, Gowan; and Lescosan, Lesco, Cleveland, OH), dithiopyr (S,S′-dimethyl 2-difluoromethyl-4-isobutyl-6-trifluoromethylpyridine-3,5-dicarbothioate; Dimension, Dow), napropamide [(RS)-N,N-diethyl-2-(1-naphthyloxy)propionamide; Devrinol, United Phosphorus, King of Prussia, PA], oxadiazon [5-tert-butyl-3-(2,4-dichloro-5-isopropoxyphenyl)-1,3,4-oxadiazol-2(3H)-one; Ronstar, Bayer], pendimethalin [N-(1-ethylpropyl)-2,6-dinitro-3,4-xylidine; Pendulum, BASF; Pre-M, BASF; Weedgrass Control, Scotts], prodiamine (5-dipropylamino-a,a,a-trifluoro-4,6-dinitro-o-toluidine; Barricade, Syngenta), and siduron [1-(2-methylcyclohexyl)-3-phenylurea]}. Using a split application strategy for some preemergence herbicides can be advantageous (Fagerness, 2002; Prinster, 1994). The split application of a preemergence herbicide may provide a consistent threshold level of active ingredient in soil for the duration of the germination cycle of the weed. Characteristics of several families of preemergence herbicides applied to tall fescue turfs are presented in Table 26-3.

The susceptibility of grassy and broadleaf weeds to preemergence herbicides varies with the location and season of application. The reader is advised to consult with local Agricultural Extension personnel for recommended herbicides, application rates, and the appropriate timing for maximum effect without injury to the tall fescue turf.

The time interval that must elapse between application and planting varies among preemergence herbicides. Benefin and bensulide should not be applied in the spring to tall fescue turfs seeded or interseeded the previous fall. Dithiopyr may be applied to newly planted tall fescue turfs that have been mowed at least twice. Similarly, the application of pendimethalin should be delayed until a new tall fescue turf has been mowed at least four times. Prodiamine should not be applied within 60 d after seeding or until after the second mowing, whichever is longer. Napropamide should not be applied to tall fescue turfs less than 3 mo old.

Postemergence Herbicides. Several herbicides have been registered for the control of emerged broadleaf weeds in tall fescue turf since the discovery of 2,4-D in 1942 (Fagerness and Johns, 2004). Like 2,4-D, MCPA (4-chloro-o-tolyloxyacetic acid) is a phenoxy herbicide that, once absorbed by leaves and roots, is translocated to meristematic regions of plants. Differences in MCPA interception, metabolism, penetration, and translocation contribute to varying levels of herbicide sensitivity among weed species. The herbicide MCPA is available in amine, ester, and sodium salt formulations, and in mixtures with other postemergence herbicides including 2,4-D, MCPP (mecoprop), and dicamba (Banvel). Generally, the ester formulation of MCPA is absorbed faster than either the amine or sodium salt formulations (McCarty et al., 1997). Mecoprop, another selective, hormone-type phenoxy herbicide, is absorbed by leaves and translocated to roots where it affects enzyme activity and plant growth (Kidd and James, 1991). Dicamba, a member of the benzoic acid herbicide family, controls several broadleaf weed species, such as broadleaf plantain (Plantago major L.), ground ivy (Glechoma hederacea L.), and smooth bedstraw (Galium mollugo L.), which are not easily controlled with 2,4-D or MCPP. The reader is advised to consult with local Agricultural Extension personnel for recommended postemergence herbicides, application rates, and the appropriate timing for maximum effect without injury to the tall fescue turf.

Fenoxyprop [(RS)-2-[4-(6-chloro-1,3-benzoxazol-2-yloxy)phenoxy]propionic acid; Acclaim, Extra, Bayer], quinclorac (Drive), DSMA (disodium methylarsonate; DSMA 4, Helena Chemical, Memphis, TN), and MSMA (sodium hydrogen methylarsonate; Bueno and Daconate, KMG-Bernuth, Houston, TX) are labeled for the control of emerged crabgrasses (Digitaria spp.) in tall fescue turf. The addition of methylated seed oil at 1.8 L/ha (1.5 pt/acre) to a spray solution containing quinclorac is recommended to enhance herbicide performance.

The herbicide bentazon [3-isopropyl-1H-2,1,3-benzothiadiazin-4(3H)-one 2,2-dioxide; Basagran T/O, BASF and Lescogran) controls annual sedge (Cyperus compressus L.) and yellow nutsedge (C. esculentus L.) in tall fescue turf. In addition to annual sedge and yellow nutsedge, the postemergence herbicides halosulfuron [3-chloro-5-(4,6-dimethoxypyrimidin-2-ylcarbamoylsulfamoyl)-1-methylpyrazole-4-carboxylic acid; Sedgehammer, Gowan] and MSMA are labeled for the control of purple nutsedge (C. rotundus L.) and kyllinga species.