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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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Ethan T. Parker, J. Scott McElroy and Michael L. Flessner

Smooth crabgrass (Digitaria ischaemum) and goosegrass (Eleusine indica) are problematic weeds in creeping bentgrass (Agrostis stolonifera) because of limited herbicide options for postemergence (POST) control and turfgrass injury potential. Metamifop is a herbicide currently being considered for release to markets in the United States but information is lacking on the most effective rates and application timings for smooth crabgrass and goosegrass control in creeping bentgrass. Field trials were conducted in Auburn, AL in 2009 and 2013 to evaluate metamifop rates (200 to 800 g·ha−1) and single or sequential application timings compared with fenoxaprop (51 to 200 g·ha−1) at two different mowing heights. Metamifop applied twice and three times sequentially at 200 g·ha−1 provided the greatest smooth crabgrass (>97%) and goosegrass (>90%) control at rough (1½ inch) and green (1/8 inch) mowing heights without unacceptable creeping bentgrass injury at 56 days after initial treatment. All treatments caused <20% visible injury on creeping bentgrass at both mowing heights except the highest rate of metamifop. Smooth crabgrass control at the green mowing height was greater than at the rough mowing height, especially at lower metamifop rates with a single application.

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Kenneth Cropper, Gregg Munshaw and Michael Barrett

Smooth crabgrass ( Digitaria ischaemum ) is a common summer annual weed found throughout much of the United States. Its long leaves and prostrate growth give it the potential to become a serious problem in both closely mowed areas such as greens or

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Charles L. Webber III, Merritt J. Taylor and James W. Shrefler

Squash (Cucurbita pepo) producers could benefit from additional herbicide options that are safe to the crop and provide effective weed control. Research was conducted in southeastern Oklahoma (Atoka County, Lane, OK) during 2010 and 2011 to determine the impact of pelargonic acid (PA) on weed control efficacy, crop injury, and squash yields. The experiment included PA applied unshielded postdirected at 5, 10, and 15 lb/acre, plus an untreated weedy control and an untreated weed-free control. ‘Enterprise’ yellow squash was direct-seeded in single rows into raised beds. Weeds included smooth crabgrass (Digitaria ischaemum), cutleaf groundcherry (Physalis angulata), spiny amaranth (Amaranthus spinosus), and yellow nutsedge (Cyperus esculentus). Pelargonic acid was applied each year in mid-July and then reapplied 8 days later. The maximum smooth crabgrass control (98%), broadleaf weed control (94%), and yellow nutsedge control (41%) was observed with the 15-lb/acre PA treatment at 9 days after initial spray treatment (DAIT), 1 day after sequential treatment (1 DAST). Pelargonic acid at 15 lb/acre provided equal or slightly greater smooth crabgrass and broadleaf (cutleaf groundcherry and spiny amaranth) control compared with the 10-lb/acre application, and consistently greater control than the 5-lb/acre rate and the weedy control. Pelargonic acid was less effective at controlling yellow nutsedge than smooth crabgrass and broadleaf weeds. Yellow nutsedge control peaked at 9 DAIT (1 DAST) with 10-lb/acre PA (41%). As the rate of PA increased from 5 to 15 lb/acre, yellow nutsedge control also increased significantly for all observation dates, except for 28 DAIT. Increasing the PA application rate increased the crop injury rating at 1 and 3 days after each application (1 and 3 DAIT, 1 and 3 DAST). Maximum squash injury occurred for each application rate at 9 DAIT (1 DAST) with 4.4%, 8.0%, and 12.5% injury for PA rates 5, 10, and 15 lb/acre, respectively. The 10-lb/acre PA treatment produced the highest squash yields (kilograms per hectare) and fruit number (fruit per hectare) compared with either the 5- or 15-lb/acre rates, and equivalent yields and fruit number as the hand-weeded weed-free treatment. The 10-lb/acre PA rate applied in a timely sequential application has the potential of providing good weed control with minimal crop injury resulting in yields equivalent to weed-free hand-weeding conditions.

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Charles L. Webber III, Merritt J. Taylor and James W. Shrefler

Pepper (Capsicum annuum) producers would benefit from additional herbicide options that are safe to the crop and provide effective weed control. Research was conducted in southeastern Oklahoma (Atoka County, Lane, OK) during 2010 and 2011 to determine the impact of pelargonic acid on weed control efficacy, crop injury, and pepper yields. The experiment included pelargonic acid applied unshielded postdirected at 5, 10, and 15 lb/acre, plus an untreated weedy control and an untreated weed-free control. ‘Jupiter’ sweet bell pepper, a tobacco mosaic virus-resistant sweet pepper with a 70-day maturity, was transplanted into single rows on 3-ft centered raised beds with 18 inches between plants (9680 plants/acre) on 28 May 2010 and 27 May 2011, respectively. Weeds included smooth crabgrass (Digitaria ischaemum), cutleaf groundcherry (Physalis angulata), spiny amaranth (Amaranthus spinosus), and yellow nutsedge (Cyperus esculentus). Pelargonic acid was applied postdirected each year in mid-June and then reapplied 8 days later. The 15-lb/acre pelargonic acid treatment resulted in the maximum smooth crabgrass control (56%) and broadleaf weed control (66%) at 1 day after the initial spray treatment (DAIT), and 33% yellow nutsedge control at 3 DAIT. Pelargonic acid at 15 lb/acre provided equal or slightly greater smooth crabgrass and broadleaf (cutleaf groundcherry and spiny amaranth) control compared with the 10-lb/acre application, and consistently greater control than the 5-lb/acre rate and the weedy control. Pelargonic acid was less effective at controlling yellow nutsedge than smooth crabgrass and broadleaf weeds. As the rate of pelargonic acid increased from 5 to 15 lb/acre, yellow nutsedge control also increased significantly for all observation dates. Increasing the pelargonic acid application rate increased the crop injury rating. The maximum crop injury occurred for each application rate at 1 DAIT with 7%, 8.0%, and 13.8% injury for pelargonic acid rates 5, 10, and 15 lb/acre, respectively. There was little or no new crop injury after the second postdirected application of pelargonic acid and crop injury following 3 DAIT for application rates was 2% or less. Only the 15-lb/acre pelargonic acid application produced greater fruit per hectare (4784 fruit/ha) and yields (58.65 kg·ha−1) than the weedy control (1196 fruit/ha and 19.59 kg·ha−1). The weed-free yields (7176 fruit/ha, 178.11 kg·ha−1, and 24.82 g/fruit) were significantly greater than all pelargonic acid treatments and the weedy control. Pelargonic acid provided unsatisfactory weed control for all rates and did not significantly benefit from the sequential applications. The authors suggest the pelargonic acid be applied to smaller weeds to increase the weed control to acceptable levels (>80%).

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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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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).

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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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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).