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James T. Brosnan, Gregory K. Breeden, and Patrick E. McCullough

Smooth crabgrass [ Digitaria ischaemum (Schreb) Schreb. ex Muhl.] infestations are common in golf course, athletic field, and landscape turf ( McCarty et al., 2005 ). Smooth crabgrass is similar to large crabgrass ( Digitaria sanguinalis L. Scop

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P.H. Demoeden, M.J. Mahoney, and M.J. Carroll

Fenoxaprop (0.027, 0.036, and 0.045 kg·ha-1) was field-applied at either of 2-, 3-, or 4-week intervals to perennial ryegrass (Lolium perenne L.) naturally infested with smooth crabgrass [Digitaria ischaemum (Schreb.) Muhl.] in Maryland (Easton and Silver Spring) during 1989 and 1990. In 1989, fenoxaprop applied at 2- or 3-week intervals at 0.027 kg·ha-1 provided fair (>74%) to good (>80%) smooth crabgrass control. Fenoxaprop applied at 0.036 or 0.045 kg·ha-1 at 2- or 3week intervals provided good to excellent (> 90%) smooth crabgrass control. Four-week intervals generally provided control that was inferior to the shorter application intervals at Silver Spring but not at Easton. In 1990, all rates provided good to excellent smooth crabgrass control when applied at 2- or 3-week intervals in Easton. At Silver Spring, where smooth crabgrass levels were very high, >88% control was provided by 0.036 kg·ha-1 applied at a 2-week interval and by 0.045 kg·ha-1 applied at either a 2- or 3-week interval. Chemical name used: [±]-2-[4-[(6 chloro-2 benzoxazolyl)oxy]phenoxy] propanoic acid (fenoxaprop).

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P.H. Dernoeden and M.A. Fidanza

Fenoxaprop is used on turfgrasses to control smooth crabgrass [Digitaria ischaemum (Schreb. ex Sweib.) Schreb. ex Muhl.] and other annual grass weeds. Our objective was to determine if a broadleaf weed herbicide (BWH = 2,4-D + mecoprop + dicamba) would affect fenoxaprop activity. The BWH was applied several days or weeks before and after fenoxaprop was applied. Smooth crabgrass control by fenoxaprop was reduced significantly when the BWH was applied ≤14 days before fenoxaprop was applied. Extremely poor crabgrass control occurred when fenoxaprop was tank-mixed with the BWH. There was no reduction in crabgrass control when the BWH was applied 21 days before or ≥3 days after fenoxaprop. Chemical names used: ethyl ester of (±)-2-[4-[(6-chloro-2-benzoxazolyl)oxy]phenoxy]propanoic acid (fenoxaprop); 2,4-dichlorophenoxy acetic acid (2,4-D); (+)-2-(4-chloro-2-methylphenoxy)propanoic acid (mecoprop); 3,6-dichloro-2-methoxybenzoic acid (dicamba).

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P.H. Dernoeden and M.J. Carroll

In this field study, five preemergence and two postemergence herbicides were evaluated for their ability to hasten Meyer zoysiagrass (Zoysia japonica Steud.) sod development when sod was established from the regrowth of rhizomes, sod strips, and loosened plant debris. Herbicide influence on zoysiagrass re-establishment was examined using two postharvest field preparation procedures as follows: area I was raked to remove most above-ground sod debris, whereas in adjacent area II sod debris was allowed to remain in place. Herbicides that controlled smooth crabgrass [Digitaria ischaemum (Schreb.) Muhl.] generally enhanced zoysiagrass cover by reducing weed competition. Meyer established from rhizomes, sod strips, and loosened plant debris, and treated with herbicides, had a rate of sod formation equivalent to that expected in conventionally tilled, planted, and irrigated Meyer sod fields. Effective smooth crabgrass control was achieved when the rates of most preemergence herbicides were reduced in the 2nd year. Chemical names used: dimethyl 2,3,5,6-tetrachloro-1,4-benzenedicarboxylate (DCPA); 3,5,-pyridinedicarbothioic acid, 2-[difluromethyl]-4-[2-methyl-propyl]-6-(trifluoromethyl)∼S,S-dimethyl ester (dithiopyr); [±]-ethyl 2-[4-[(6-chloro-2-benzoxazolyl)oxy]phenoxy] propanoate (fenoxaprop); 3-[2,4-dichloro-5-(1-methylethoxy)phenyl]-5-(1,1-dimethylethyl)-1,3,4-oxadiazol-2-(3H)-one (oxadiazon); N-[1-ethylpropyl)-3,4-dimethyl-2,6-dinitrobenzenamine(pendimethalin);N3,N3-di-n-propyl-2,4-dinitro-6-[trifluromethyl)-m-phenylenediamine (prodiamine); and 3,7-dichloro-8-quinolinecarboxylic acid (quinclorac).

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J.M. Goatley Jr. and R.E. Schmidt

Research was conducted to evaluate crabgrass [Digitaria ischaemum (Schreb.) Muhl.] control, incidental dollar spot (incited by Lanzia and Moellerodiscus spp.) suppression, and turfgrass quality following sequential, low-level postemergence applications of DSMA to creeping bentgrass (Agrostis stolonifera var. palustris Farwell). DSMA was applied at 22 mg·m-2 at 7-day intervals for 15 consecutive weeks (DSMA-W) from May through Aug. 1986 and 1987 and for 10 consecutive weeks from June through Aug. 1988. DSMA also was applied in three split applications of 110 mg·m-2 every 10 days (DSMA-S) in June and July of each year. DCPA was applied in a single, preemergence application in May as a comparative standard for crabgrass control. Percent crabgrass in either DSMA-treated plot was 20% by 11 Sept., an infestation that was unacceptable for high-quality turf. Percent crabgrass infestation was 6% at all rating dates in 1987 or 1988 for DSMA-W and 11% at all dates in 1987 or 1988 for DSMA-S. DCPA significantly reduced percent crabgrass as compared to the nontreated control at all rating dates, but the percent crabgrass ratings tended to be higher than those for either DSMA treatment by the final rating dates of each year. The DSMA treatments significantly reduced dollar spot incidence in each year. Turfgrass discoloration was observed following the DSMA-S treatment in July 1987 as compared to the control, but the turf quality recovered by August. Turfgrass quality was higher for DSMA treatments than for either DCPA or the nontreated control due to season-long crabgrass control and disease suppression. Chemical names used: disodium methanearsonate (DSMA), dimethyl tetrachloroterephthalate (DCPA).

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Peter H. Dernoeden, Cale A. Bigelow, John E. Kaminski, and John M. Krouse

Smooth crabgrass [Digitaria ischaemum (Schreber) Schreber ex Muhlenb.] is an invasive weed of cool-season turfgrasses. Previous research has demonstrated that quinclorac is an effective postemergence herbicide for crabgrass control, but performance has been erratic in some regions. Furthermore, quinclorac may elicit objectionable levels of discoloration in creeping bentgrass (Agrostis stolonifera L.). The objectives of this 3-year field study were to determine optimum rates and timings of quinclorac applications that provide consistent levels of effective crabgrass control and to assess creeping bentgrass quality responses to quinclorac. To evaluate crabgrass control, quinclorac was applied in early-, mid- and late-postemergence timings at various rates to a perennial ryegrass (Lolium perenne L.) turf. Similar treatments were applied to creeping bentgrass to determine if application timing and rate influenced the level and duration of discoloration. Quinclorac was applied alone or was tank-mixed with either urea (N at 6.1 kg·ha-1) or chelated iron (Fe)+nitrogen (N) (FeSO4 at 1.1 kg·ha-1+N at 2.2 kg·ha-1) to determine if they would mask discoloration. Crabgrass control generally was more effective in the early- and midpostemergence application timings. A single application of quinclorac (0.84 kg·ha-1) was effective where crabgrass levels were moderate, but sequential (i.e. multiple) applications were required where crabgrass levels were severe. The most consistent level of crabgrass control where weed pressure was severe occurred with three, sequential quinclorac (0.37 or 0.42 kg·ha-1) applications. Creeping bentgrass exhibited 2 to 11 weeks of unacceptable discoloration in response to sequential quinclorac applications. Chelated Fe+N was more effective than urea in masking discoloration. In general, chelated Fe+N tank-mixed with quinclorac masked discoloration and turf had quality equivalent to untreated bentgrass on most, but not all rating dates. Chemical names used: 3,7,-dichloro-8-quinolinecarboxylic acid (quinclorac).

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S. Alan Walters, Scott A. Nolte, and Bryan G. Young

The influence of `Elbon', `Maton', and `Wheeler' winter rye (Secale cereale) with or without herbicide treatments on weed control in no-tillage (NT) zucchini squash (Cucurbita pepo) was determined. `Elbon' or `Maton' produced higher residue biomass, greater soil coverage, and higher weed control compared with `Wheeler'. Although winter rye alone did not provide sufficient weed control (generally <70%), it provided substantially greater redroot pigweed (Amaranthus retroflexus) and smooth crabgrass (Digitaria ischaemum) control (regardless of cultivar used) compared with no winter rye at both 28 and 56 days after transplanting (DAT). No effect (P > 0.05) of winter rye cultivar on early or total squash yield was detected. Although applying clomazone + ethalfluralin to winter rye residues improved redroot pigweed control compared with no herbicide, the level of control was generally not adequate (<85% control) by 56 DAT. Treatments that included halosulfuron provided greater control of redroot pigweed than clomazone + ethalfluralin, and redroot pigweed control from halosulfuron treatments was similar to the weed-free control. However, regardless of year or cover crop, any treatment with halosulfuron caused unacceptable injury to zucchini squash plants which lead to reduced squash yield (primarily early yields). Insignificant amounts of squash injury (<10% due to stunting) resulted from clomazone + ethalfluralin in no-tillage plots during either year. Treatments with clomazone + ethalfluralin had early and total yields that were similar to those of the weed-free control, although this herbicide combination provided less weed control compared with the weed-free control.

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Peter H. Dernoeden

Annual bluegrass (Poa annua L.) is an intractable weed problem on golf courses. Much has been written about annual bluegrass, but there is little documentation of regional germination period(s) and the proper timing of preemergence herbicides targeted for the control of the annual biotype (P. annua ssp. annua [L.] Timm.=AB). The objectives of this field study were to determine the optimum prodiamine rate and timing for effective AB control. The turf was a mature stand of `Kenblue' Kentucky bluegrass (Poa pratensis L.) maintained under conditions similar to those imposed for golf course roughs. Three rates of prodiamine (0.36,0.73, and 1.1 kg·ha-1) were applied on three dates in 1995 (11 Aug., 14 Sept., and 13 Oct.) and 1996 (29 Aug., 16 and 30 Sept.). All rates applied 11 Aug. or 14 Sept. 1995, and 29 Aug. or 16 Sept. 1996 effectively controlled AB. None of the rates applied 13 Oct. 1995 reduced AB cover, and the 0.36 kg·ha-1 rate applied 30 Sept. 1996 provided relatively poor AB control. Data and observations indicated that the major germination period for AB was between late September and early December. Effective AB control was achieved whenever prodiamine, regardless of rate, was applied between mid-August and mid-September. These prodiamine rates and this application window may be effective only in relatively high cut turf (i.e., >5.0 cm) in the mid-Atlantic region. Chemical names used: O,O-bis(1-methylethyl) S-{2-[(phenylsulfonyl)amino]ethyl} phosphorodithioate (bensulide); N 3,N 3-di-n-propyl-2,4-dinitro-6-(trifluoromethyl)-m-phenylenediamine (prodiamine).

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Julia Whitworth

The usefulness of cover crops for weed management in strawberries were evaluated. Wheat (Triticum aestevum L.), rye (Secale cereale L.), and crimson clover (Trifolium incarnatum L.) were grown in individual pots then killed by tillage or herbicide and followed in the same pots by plantings of bermuda grass [Cynodon dactylon (L.) Pers.], yellow nutsedge (Cyperus esculentus L.), crabgrass [Digitaria ischaemum (Schreb.) Schreb. ex Muhl.], or strawberries (Fragaria ×ananassa `Cardinal'). Rye and wheat tilled into the medium generally increased the growth of strawberries and decreased the growth of bermuda grass. Rye and wheat residues appeared to suppress growth of weeds and strawberries when the residues remained on the medium surface. Crimson clover had little affect on the growth of weeds or strawberries. Yellow nutsedge and crabgrass were not significantly affected by cover crop residues.

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R.J. Cooper, P.C. Bhowmik, and L.A. Spokas

Field experiments were conducted to determine the response of five widely used Kentucky bluegrass (Poa pratensis L.) cultivars (Adelphi, Baron, Bensun, Merion, and Touchdown) to preemergence applications of the herbicide pendimethalin. Pendimethalin applied during 2 years at 1.7 or 3.4 kg·ha-1 (a.i.) controlled smooth crabgrass [Digitaria ischaemum (Schreb. ex Schweig.) Schreb. ex Muhl.] effectively without injury to turf. Pendimethalin at 3.4 kg·ha-1 resulted in a short-term suppression of root growth immediately following application in the first year of the study. The reduction was transitory and subsequent rooting and rhizome growth were unaffected by pendimethalin. Cultivar × pendimethalin level interactions were not significant during the study. Thus, the herbicide appears to be a safe, effective preemergence material for crabgrass control in Kentucky bluegrass turf. Chemical name used: N-(1-ethylpropyl)-3,4-dimethyl-2,6-dinitrobenzenamine (pendimethalin).