Smooth Crabgrass Control Research Articles

Methiozolin rate and application frequency influence goosegrass (Eleusine indica) and smooth crabgrass (Digitaria ischaemum) control in turf

Abstract Methiozolin is labeled for goosegrass and smooth crabgrass control in golf course putting greens, but no peer-reviewed literature exists regarding this use. Greenhouse experiments were conducted evaluating goosegrass and smooth crabgrass response to increasing rates of methiozolin as affected by weed growth stage. In general, as weed growth stage increased, the methiozolin rate required to reduce weed biomass 90% (WR90) increased. Goosegrass was more sensitive to preemergence-applied methiozolin than smooth crabgrass, and the WR90 was 30.4 and 118 g ai ha–1 for goosegrass and smooth crabgrass, respectively. However, smooth crabgrass was generally more sensitive to postemergence-applied methiozolin than goosegrass. Subsequent field studies were conducted to evaluate goosegrass and smooth crabgrass control with methiozolin applied singularly or sequentially at standard preemergence timings. Results indicated methiozolin applied singularly or sequentially at the label-recommended rate (500 g ha–1) is not persistent enough to provide season-long control of goosegrass and smooth crabgrass. Ten field studies were conducted in Alabama, California, Florida, and Virginia to evaluate frequent methiozolin application programs with the objective of providing selective, season-long goosegrass and smooth crabgrass control. Results from these studies indicate methiozolin can be safely applied to hybrid bermudagrass and creeping bentgrass putting greens despite exceeding the yearly maximum use rate for putting greens (2,500 g ha–1) with some treatments. Methiozolin effectively controlled smooth crabgrass throughout the growing season in California and Virginia when 10 biweekly applications were applied at 250 g ha–1 or higher. In Florida, methiozolin did not acceptably (80%) control goosegrass regardless of application rate. In Virginia, methiozolin acceptably controlled goosegrass only when applied at rates and frequencies that exceeded the maximum yearly methiozolin usage rate. These data indicate that methiozolin has the potential to control smooth crabgrass preemergence when applied frequently, but does not provide acceptable goosegrass control at labeled rates.

Assessing a programmatic approach for the control of quinclorac‐resistant smooth crabgrass (Digitaria ischaemum) in established bermudagrass turf

AbstractThe auxin‐mimicking herbicide quinclorac controls crabgrass (Digitaria spp.) after emergence in cool‐ and warm‐season turfgrass species. Quinclorac resistance has been confirmed in smooth [Digitaria ischaemum (Schreb.) Muhl.] and large crabgrass [Digitaria sanguinalis (L.) Scop.]. Two Mississippi smooth crabgrass populations have been confirmed as quinclorac‐resistant. Field experiments were conducted to evaluate programmatic approaches to control one of these populations. Treatments included the sequential application of pre‐emergence herbicides on 17 Feb. and 10 Apr. 2020, and 25 Feb. and 6 Apr. 2021, alone or with 0.84 kg quinclorac ha–1 applied postemergence on 10 April 2020 and 6 April 2021, then a second application of quinclorac alone on 18 June 2020 and 16 June 2021. Pre‐emergence treatments included 0.05 kg indaziflam ha–1, 0.84 kg prodiamine ha–1, 0.56 kg dithiopyr ha–1, and 0.47 kg prodiamine ha–1 + 0.21 kg imazaquin ha–1 + 0.73 kg simazine ha–1. Commercial standards applied on 10 Apr. and 18 June 2020, and 6 Apr. and 16 June 2021 included 0.16 kg pinoxaden ha–1 and 2.27 kg monosodium methanearsonate ha–1. Four weeks after the last application, all treatments except quinclorac (2020 and 2021), dithiopyr (2020), and pinoxaden (2020) controlled quinclorac‐resistant smooth crabgrass by >90%. Various standard pre‐emergence herbicides adequately controlled the resistant population. Quinclorac combined with pre‐emergence strategies provided greater control of smooth crabgrass than quinclorac alone. Ongoing research is investigating the mechanism of quinclorac resistance. Future research should screen a wider distribution of populations and investigate cross‐ and multiple resistance.

Investigating low-dose herbicide programs for goosegrass (Eleusine indica) and smooth crabgrass (Digitaria ischaemum) control on creeping bentgrass greens

AbstractOnly four herbicides are registered for smooth crabgrass or goosegrass control on creeping bentgrass golf putting greens. None of the four herbicides control weedy grasses for the entire season or control weeds postemergence when applied once at labeled rates. Three of the product labels prohibit repeated use or application during stressful summer conditions. We hypothesized frequently applying herbicides at low doses could provide season-long control of summer grasses while minimizing turf injury. Seven field experiments were conducted on creeping bentgrass putting greens to evaluate various herbicides applied monthly, biweekly, or weekly for postemergence and residual control of goosegrass and smooth crabgrass as well as creeping bentgrass putting green tolerance. Metamifop applied twice monthly at 200 g ai ha−1, topramezone applied eight times weekly at 1.5 g ae ha−1, and siduron applied weekly at 5.6 kg ai ha−1 or four times biweekly at 11 kg ha−1 did not injure creeping bentgrass greater than 10% and maintained creeping bentgrass quality and cover equivalent to nontreated turf. Weekly or biweekly programs of fenoxaprop or quinclorac caused unacceptable injury and quality decline. Metamifop applied monthly and either fenoxaprop program controlled both smooth crabgrass and goosegrass by 97% to 99% throughout the growing season. Programs containing either quinclorac or siduron controlled smooth crabgrass by 99% to 100% but did not control goosegrass greater than 39%. All topramezone programs controlled smooth crabgrass by 69% to 77% and goosegrass by 93% to 98%. In additional studies, siduron applied five times biweekly did not injure creeping bentgrass on putting greens and controlled smooth crabgrass by more than 90% at seasonal, cumulative rates between 17 and 65 kg ai ha−1. This method of frequent, low-dose herbicide treatment to control smooth crabgrass and goosegrass on golf putting greens is novel and currently could be legally implemented with siduron.

Postemergence smooth crabgrass control is not influenced by herbicide combinations with trinexapac‐ethyl

Core Ideas Trinexapac‐ethyl (TE) is a common plant growth regulator used in turfgrass systems. The effects of TE on herbicide efficacy to control smooth crabgrass were unknown. Mixing TE with postemergence herbicides did not affect smooth crabgrass control.

Effects of preemergence herbicides on establishment of little bluestem and sideoats grama golf course rough

AbstractNative warm‐season grass (NWSG) roughs provide environmental and aesthetic value to golf courses; however, weed competition is a constraint during establishment. This research evaluated the effects of common turfgrass preemergence herbicides on establishment of newly seeded 1:1 mixture of little bluestem [Schizachyrium scoparium (Michx.) Nash] and sideoats grama [Bouteloua curtipendula (Michx.) Torr.] (14.3 lb total seed acre−1) rough. Herbicides applied immediately after drill‐seeding included: atrazine (1.0 lb a.i. acre−1), dimethenamid‐P (1.5 lb acre−1), dithiopyr (0.38 lb acre−1), imazapic (0.06 lb acre−1), indaziflam (0.029 lb acre−1), isoxaben (1.0 lb acre−1), S‐metolachlor (2.48 lb acre−1), oxadiazon (4.0 lb acre−1), pendimethalin (1.47 lb acre−1), prodiamine (0.75 lb acre−1), and simazine (1.0 lb acre−1). Effects upon NWSG plant density and biomass, as well as smooth crabgrass [Digitaria ischaemum (Schreb.) Schreb. ex Muhl.] control, were evaluated in 2017 and 2018. Across years, imazapic, dimethenamid, oxadiazon, and metolachlor controlled crabgrass >90%. In 2017, little bluestem plant density assessed 4 months after treatment was 2 to 13 times greater in imazapic‐treated plots than all other treatments except for those treated with isoxaben and simazine. Application of imazapic resulted in greater little bluestem aboveground biomass than all other herbicide treatments, except simazine, in 2017. In 2018, imazapic resulted in greater little bluestem plant density than the untreated control, atrazine, prodiamine, oxadiazon, isoxaben, or simazine. Although it was a minor component of the sward, sideoats grama was generally tolerant of imazapic. Imazapic application during seeded establishment of little bluestem and sideoats grama golf course rough provides acceptable crop tolerance and smooth crabgrass control.

Response of Six Turfgrass Species and Four Weeds to Three HPPD‐Inhibiting Herbicides

Core Ideas Tembotrione controlled weeds selectively in bluegrass, fescue, and zoysiagrass turf. Topramezone controlled key weeds better than mesotrione and tembotrione. Topramezone was among the safest herbicides on four of the six turfgrasses tested. Results will aid herbicidal‐risk assessment near potentially sensitive turfgrass species. The study supports considerations for herbicide label expansion or registration in turf. Mesotrione (2‐[4‐(methylsulfonyl)‐2‐nitrobenzoyl]‐1,3‐cyclohexanedione), tembotrione (2‐[2‐chloro‐4‐(methylsulfonyl)‐3‐[(2,2,2‐trifluoroethoxy)methyl]benzoyl]‐1,3‐cyclohexanedione), and topramezone ([3‐(4,5‐dihydro‐3‐isoxazolyl)‐2‐methyl‐4‐(methylsulfonyl)phenyl](5‐hydroxy‐1‐methyl‐1H‐pyrazol‐4‐yl)methanone) are new herbicides that control many troublesome weeds, but little is known about the response of several turfgrass species to these herbicides. A multiyear study was conducted to determine the response of six turfgrass species and four weeds to these three herbicides. Study results generally agreed with previous reports of turfgrass and weed response to mesotrione, and suggest that tembotrione could be safely used, depending on rate, to control weeds such as smooth crabgrass [Digitaria ischemum (Schreb.) Schreb. ex Muhl.], broadleaf plantain (Plantago major L.), and white clover (Trifolium repens L.) selectively in tall fescue [Schedonorus arundinaceus (Schreb.) Dumort., nom. cons.], Kentucky bluegrass (Poa pratensis L.), and zoysiagrass (Zoysia japonica Steud.) turf. Topramezone at 36.8 g a.i. ha−1 controlled smooth crabgrass and white clover better than mesotrione or tembotrione, and smooth crabgrass control by topramezone had similar results as in other studies. Predicted maximum turfgrass injury based on the Gaussian function applied over time generally showed that maximum injury caused by topramezone was less than tembotrione and mesotrione on creeping bentgrass (Agrostis stolonifera L.) and perennial ryegrass (Lolium perenne L.), less than tembotrione and equivalent to mesotrione on tall fescue and perennial ryegrass, equivalent to tembotrione and more than mesotrione on bermudagrass [Cynodon dactylon (L.) Pers.], and more than tembotrione and mesotrione on zoysiagrass. The area under the progress curve per day of visual injury and normalized difference vegetation index were consistent with trends in predicted maximum injury.

Goosegrass and Bermudagrass Response to Rates and Tank Mixtures of Topramezone and Triclopyr

Postemergence herbicide options for mature goosegrass [Eleusine indica (L.) Gaertn.] control in bermudagrass (Cynodon spp. Rich.) turf are lacking. Greenhouse and field trials were conducted to determine the lowest rate at which topramezone, with or without triclopyr, controls goosegrass while maintaining acceptable bermudagrass quality. Greenhouse dose–response studies determined herbicide rates for field trials. In field trials, topramezone at 6.13 to 12.3 g a.i. ha−1 applied twice at a 3‐wk interval eliminated 8‐ to 18‐tiller goosegrass at three of four locations. The same topramezone treatments did not reduce smooth crabgrass [Digitaria ischaemum (Schreb.) Schreb. ex Muhl.] cover more than 53% when applied alone and not more than 84% when applied with triclopyr at 140 g acid equivalent ha−1. The number of days over a threshold of 30% injury or stunting (DOT30) within the 28‐d period following each of two herbicide treatments was calculated for 31 bermudagrass varieties. Bermudagrass injury DOT30 following the first treatment ranged from 11.1 to 17.8 d, depending on variety. The addition of triclopyr increased injury DOT30 but reduced the severity of discoloration by eliminating white tissue discoloration. All varieties were severely injured but completely or near completely recovered by 28 d after each treatment. Generally, topramezone at 6.13 or 12.3 g a.i. ha−1 applied twice controls goosegrass in bermudagrass. Addition of triclopyr improves smooth crabgrass control and decreases severity of bermudagrass injury but increases suprathreshold‐injury duration.

Triclopyr Reduces Foliar Bleaching from Mesotrione and Enhances Efficacy for Smooth Crabgrass Control by Altering Uptake and Translocation

Turfgrass managers can reduce foliar bleaching of smooth crabgrass from mesotrione by tank-mixing triclopyr ester with applications. These tank mixtures also have potential to enhance smooth crabgrass control compared to mesotrione alone. The objectives of this research were to evaluate the influence of triclopyr on the efficacy, absorption, and translocation of mesotrione in multitiller smooth crabgrass. In field experiments, tank-mixing triclopyr at 560 or 1,120 g ae ha−1with mesotrione at 140 g ai ha−1applied sequentially or at 280 g ha−1applied singly provided excellent control (> 90%) of multitiller smooth crabgrass in tall fescue. These treatments were more effective than mesotrione alone and fenoxaprop at 195 g ai ha−1that averaged 66 and 81% control after 6 wk, respectively. Mesotrione alone at 280 g ha−1bleached smooth crabgrass 53% at 2 wk after initial treatment (WAIT), and was 14% greater than the 140 g ha−1treatment. Sequential treatments of the low mesotrione rate bleached smooth crabgrass 16 to 22% from 3 to 5 WAIT. Triclopyr tank mixtures reduced smooth crabgrass bleaching from mesotrione on all dates to < 5%. Tall fescue injury was not detected at any evaluation date. In laboratory experiments, smooth crabgrass reached peak foliar absorption of14C-mesotrione at 24 and 168 h after treatment (HAT; 23% and 15%) when mesotrione was applied with triclopyr at 1,120 and 0 g ha−1, respectively. Triclopyr reduced translocation of radioactivity 12% at 72 and 168 HAT, compared to14C-mesotrione alone. Enhanced foliar uptake of mesotrione from triclopyr tank mixtures might improve control of multitiller smooth crabgrass compared to mesotrione alone. Reduced foliar bleaching from triclopyr is associated with less translocation of mesotrione or derivatives in smooth crabgrass.

Flumioxazin Tank-Mixtures with Six Herbicides for Annual Bluegrass (Poa annua) Control in Bermudagrass

Flumioxazin is a protoporphyrinogen oxidase inhibitor with potential for POST annual bluegrass control and PRE smooth crabgrass control in bermudagrass. However, flumioxazin applications are often less effective in winter, compared with fall, because of reduced efficacy on mature annual bluegrass. The objective of this research was to evaluate tank-mixtures of flumioxazin with six other herbicide mechanisms of action for POST annual bluegrass control in late winter and residual smooth crabgrass control. Flumioxazin at 0 or 0.42 kg ai ha−1was evaluated in combination with flazasulfuron at 0.05 kg ai ha−1, glufosinate at 1.26 kg ai ha−1, glyphosate at 0.42 kg ae ha−1, mesotrione at 0.28 kg ai ha−1, pronamide at 1.68 kg ai ha−1, or simazine at 1.12 kg ai ha−1. Flumioxazin alone controlled annual bluegrass 61 to 70% at 8 wk after treatment (WAT) in three experiments from 2012 to 2014 in central Georgia. Flumioxazin tank-mixed with flazasulfuron, glyphosate, glufosinate, pronamide, and simazine provided good (80 to 89%) to excellent (> 90%) control of annual bluegrass at 8 WAT in 2 of 3 yr. These tank-mixtures were also more effective than flumioxazin alone in 2 of 3 yr, and control was greater or equal to the tank-mix partners applied alone. Treatments that included flumioxazin provided excellent (≥ 90%) control of smooth crabgrass at 6 mo after treatment in all 3 yr. Overall, tank-mixing flumioxazin with other herbicide chemistries may improve POST annual bluegrass control, compared with exclusive treatments, and effectively control smooth crabgrass in bermudagrass.

Metamifop Rates, Application Timings, and Broadleaf Herbicide Admixtures Affect Smooth Crabgrass Control in Turf

Metamifop is an aryloxyphenoxypropionate herbicide under evaluation in the United States for annual grass control in cool-season turfgrasses. Insufficient information is available on the most effective metamifop application timings and mixtures for POST smooth crabgrass control. Field trials conducted in Blacksburg, VA, evaluated metamifop for smooth crabgrass control in existing stands of perennial ryegrass, Kentucky bluegrass, and tall fescue at three rates compared to fenoxaprop, metamifop applied twice at three application intervals, and metamifop in combination with the broadleaf herbicides carfentrazone, 2,4-D plus dicamba plus mecoprop (DDM), and mesotrione. Smooth crabgrass control was equivalent with metamifop at 400 g ai ha−1and fenoxaprop at 195 g ai ha−1. Smooth crabgrass cover was 2% or less, 12 wk after initial treatment, when treated twice with metamifop (300 g ha−1) at a 3-, 6-, or 8-wk interval and significantly better than metamifop applied once. Smooth crabgrass cover was significantly greater at every assessment date in plots treated with metamifop plus DDM than all other metamifop plus broadleaf herbicide admixtures. Metamifop did not appear to significantly injure any turfgrass in these studies, but conclusions about metamifop safety to cool-season turfgrasses cannot be made from these studies due to nonreplication of turfgrass species. According to these data, metamifop is an effective herbicide for controlling smooth crabgrass in cool-season turfgrasses when applied once at 300 or 400 g ha−1or twice at a 3-, 6-, or 8-wk interval. Although metamifop continues to control smooth crabgrass when added to some broadleaf herbicides, smooth crabgrass control was reduced when metamifop was combined with DDM.

Weed Control in Sweet Bell Pepper Using Sequential Postdirected Applications of Pelargonic Acid

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%).

Dithiopyr Efficacy, Absorption, and Fate in Annual Bluegrass, Goosegrass, Smooth Crabgrass, and Tall Fescue

Dithiopyr provides pre‐ and early postemergence (POST) control of smooth crabgrass [Digitaria ischaemum (Schreb.) Schreb. ex Muhl] in tall fescue (Festuca arundinacea Schreb.), and may allow greater application flexibility in spring than other herbicides. Dithiopyr also provides preemergence (PRE) control of annual bluegrass (Poa annua L.) and goosegrass [Eleusine indica (L.) Gaertn.], but POST applications are ineffective and may result from differential physiological fate compared to smooth crabgrass. Experiments were conducted to investigate efficacy, absorption, distribution, and metabolism of dithiopyr in annual bluegrass, goosegrass, smooth crabgrass, and tall fescue. From seven dithiopyr rates, 1.18, 1.03, 0.76, and >4.48 kg a.i. ha−1 were required to reduce shoot mass 50% from the nontreated for annual bluegrass, goosegrass, smooth crabgrass, and tall fescue, respectively. In laboratory experiments, smooth crabgrass had ≈75% more kBq kg−1 following root absorption of 14C‐dithiopyr than annual bluegrass, goosegrass, and tall fescue after 72 h. All species recovered >90% of foliar‐absorbed 14C in the treated leaf after 72 h, with limited 14C recovery (≤5%) in roots and nontreated shoots. Metabolism of dithiopyr increased from 1 to 7 d after treatment (DAT) in all grasses. Final metabolism measured 69, 52, 33, and 27% of total 14C recovered in smooth crabgrass, goosegrass, annual bluegrass, and tall fescue, respectively. Results suggest relative herbicide concentration and greater metabolism is associated with dithiopyr selectivity for POST control of smooth crabgrass compared to other grassy weeds in turf.

Dithiopyr Behavior in Smooth Crabgrass (Digitaria ischaemum) as Influenced by Growth Stage and Temperature

Dithiopyr provides PRE and early POST control of smooth crabgrass, but POST efficacy is often inconsistent on tillered plants. Experiments were conducted to evaluate the interaction of temperature and growth stage on dithiopyr efficacy, absorption, translocation, and metabolism in smooth crabgrass. In greenhouse experiments, I50(predicted rate to induce 50% injury) measured < 0.14, 0.14, and 0.15 kg ha−1at low temperatures (average 23 C) for multi-leaf, one-tiller, and multi-tiller smooth crabgrass, respectively, while I50measured < 0.14, 0.88, and > 2.24 kg ha−1at high temperatures (average 32 C), respectively. Multi-tiller (three to five tillers) smooth crabgrass absorbed more root applied14C-dithiopyr than multi-leaf (three to four leaves) and one-tiller plants, but specific radioactivity (Bq mg−1) was two to three times greater in multi-leaf plants compared to tillered plants. Smooth crabgrass treated at 15/10 C (day/night) had ≈ two times greater specific radioactivity following root applied14C-dithiopyr than at 30/25 C. Radioactivity distribution to shoots from root applications measured 43, 30, and 20% of the total absorbed for multi-leaf, one-tiller, and multi-tiller plants, respectively. Smooth crabgrass had two times more foliar absorption of14C-dithiopyr at 15/10 than 30/25 C while14C losses were greater at 30/25 than 15/10 C. Smooth crabgrass metabolism of14C-dithiopyr was ≈ two times greater at 30/25 than 15/10 C, and multi-leaf plants averaged 10 to 20% more metabolism than tillered plants at 7 d after treatment. Results suggest differential absorption, translocation, and metabolism may contribute to dithiopyr efficacy on smooth crabgrass at various growth stages, but use under high temperatures (30/25 C) could increase losses from volatilization, reduce foliar absorption, and increase metabolism compared to cooler temperatures (15/10 C).

Weed Control in Yellow Squash Using Sequential Postdirected Applications of Pelargonic Acid

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.

Evaluation of Adjuvants on Flumioxazin Efficacy for Postemergence Annual Bluegrass and Residual Smooth Crabgrass Control

Evaluation of Adjuvants on Flumioxazin Efficacy for Postemergence Annual Bluegrass and Residual Smooth Crabgrass Control

Aminocyclopyrachlor Efficacy for Controlling Virginia Buttonweed (Diodia virginiana) and Smooth Crabgrass (Digitaria ischaemum) in Tall Fescue

Virginia buttonweed and smooth crabgrass are problematic weeds in tall fescue and may warrant control with herbicides at similar timings. The objectives of these field experiments were to evaluate (1) aminocyclopyrachlor rate and application regimens for controlling Virginia buttonweed and (2) the influence of growth stage on aminocyclopyrachlor efficacy for controlling smooth crabgrass. Single applications of aminocyclopyrachlor at 0.05 and 0.08 kg ai ha−1 provided poor (< 70%) and fair (70 to 79%) control of Virginia buttonweed, respectively, but sequential applications improved control to 83 to 99%. Single and sequential applications of aminocyclopyrachlor at 0.11 kg ai ha−1 provided good (80 to 89%) and excellent (> 90%) control of Virginia buttonweed, respectively. Aminocyclopyrachlor at 0.11 kg ha−1 provided fair control of smooth crabgrass at the multileaf growth stage prior to tillering but control was poor when applied at the multitiller stage. Aminocyclopyrachlor at 0.05 and 0.08 kg ha−1 provided poor control of crabgrass at both timings and were less effective than fenoxaprop at 0.10 kg ai ha−1.

Efficacy of Corn Gluten Meal for Common Dandelion and Smooth Crabgrass Control Compared to Nitrogen Fertilizers

Efficacy of Corn Gluten Meal for Common Dandelion and Smooth Crabgrass Control Compared to Nitrogen Fertilizers

Application Placement Affects Postemergence Smooth Crabgrass (Digitaria ischaemum) and Annual Bluegrass (Poa annua) Control with Indaziflam

Greenhouse experiments were conducted to determine the effects of herbicide placement on POST smooth crabgrass and annual bluegrass control. Soil-plus-foliar, soil-only, and foliar-only applications of indaziflam (52.5 g ai ha−1), dithiopyr (560 ai g ha−1), or quinclorac (840 g ai ha−1) were made to one-tiller smooth crabgrass plants. Similarly, indaziflam (52.5 g ha−1), foramsulfuron (29 g ai ha−1), or prodiamine (840 g ai ha−1) were applied to nontillering annual bluegrass plants in an identical manner. No differences in smooth crabgrass control were detected between soil-plus-foliar and soil-only applied indaziflam from 21 to 35 d after treatment (DAT). By 28 DAT, smooth crabgrass control and biomass reductions with these indaziflam treatments were ≥ 90% and not different than quinclorac. Comparatively, smooth crabgrass control with foliar-only applications of indaziflam never exceeded 28%. Responses on annual bluegrass were similar as soil-plus-foliar and soil-only applied indaziflam exhibited greater efficacy than indaziflam applied foliar-only. By 28 DAT, annual bluegrass control and aboveground biomass reductions with soil-plus-foliar and soil-only treatments were ≥ 86% and not different from foramsulfuron. Comparatively, foliar-only applications of indaziflam controlled annual bluegrass ≤ 2%. These results indicate that root absorption is required for POST control of smooth crabgrass and annual bluegrass with indaziflam. Further research is needed to determine if techniques to enhance indaziflam contact with soil will enhance POST smooth crabgrass and annual bluegrass control in the field.

Nitrogen-Enhanced Efficacy of Mesotrione and Topramezone for Smooth Crabgrass (Digitaria ischaemum) Control

The herbicides mesotrione and topramezone inhibit 4-hydroxyphenylpyruvate dioxygenase (HPPD) and have efficacy against smooth crabgrass. Research was conducted to determine the impacts of soil-applied nitrogen (N) fertilizer on the effectiveness of single applications of mesotrione and topramezone for postemergence smooth crabgrass control. Field experiments in 2010 and 2011 evaluated the efficacy of mesotrione (280 g a.i. ha−1) and topramezone (9 g a.i. ha−1) for control of multitiller smooth crabgrass subjected to five N fertility treatments (0, 12, 25, 37, or 49 kg N ha−1). Greenhouse experiments evaluated the response of smooth crabgrass to mesotrione (0, 70, 140, 280, 560, and 1,120 g ha−1) and topramezone (0, 4.5, 9, 18, 36, and 72 g ha−1) with 0 or 49 kg N ha−1. Further research evaluated changes in smooth crabgrass leaf tissue pigment concentrations following treatment with mesotrione (280 g ha−1) and topramezone (18 g ha−1) with 0 or 49 kg N ha−1. In field experiments, N increased smooth crabgrass control with mesotrione and topramezone for 8 wk; however, increasing N rate above 25 kg ha−1did not improve control on any rating date. In dose-response experiments, N application reduced I50values for mesotrione and topramezone by 67 and 53%, respectively, 21 d after treatment (DAT). Reductions in aboveground biomass with both herbicides were greater when applied following N treatment as well. In leaf-response experiments, N decreased new leaf chlorophyll and carotenoid concentrations and new leaf production after treatment with topramezone. Future research should investigate whether increased translocation of these herbicides to meristimatic regions contribute to N-enhanced efficacy.

Sodium Chloride Efficacy for Smooth Crabgrass (Digitaria ischaemum) Control and Safety to Common Bermudagrass and Seashore Paspalum

Seashore paspalum has high salinity tolerance, suggesting sodium chloride might have potential as a selective grassy weed herbicide. The objective of this research was to investigate sodium chloride rate and application timing for smooth crabgrass control and seashore paspalum and common bermudagrass injury. Five rates of sodium chloride (244, 488, 976, 1,952, or 3,904 kg ha−1) were compared with quinclorac at 0.84 kg ai ha−1 for controlling multileaf or multitiller smooth crabgrass. Sodium chloride at ≥ 976 kg ha−1 provided excellent control (90 to 100%) of multitiller smooth crabgrass from 7 to 28 d after treatment, but ≥ 1,952 kg ha−1 was required to achieve excellent control of multileaf populations. Furthermore, 976 kg ha−1 of sodium chloride applied to multitiller smooth crabgrass caused minimal seashore paspalum injury (0 to 6%), comparable to quinclorac, but was more injurious when applied earlier in the spring for multileaf smooth crabgrass control. Common bermudagrass injury increased with sodium chloride rate and was > 20% from sodium chloride at 488 and 976 kg ha−1 at both application timings. Overall, sodium chloride was most effective and safe on seashore paspalum when applied for smooth crabgrass control at the multitiller growth stage, whereas bermudagrass injury might be excessive at minimum rates required for control.