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Praxelis is an annual to short-lived perennial herb in the Asteraceae family and an emerging problematic weed species in Florida nurseries. The objective of these experiments was to determine efficacy of selected PRE and POST herbicides for control of praxelis. An additional experiment was conducted to determine efficacy of the same PRE herbicides for control of bluemink, a weed similar in appearance to praxelis that is also common in Florida. The granular herbicides dimethenamid + pendimethalin, flumioxazin, oxyfluorfen + pendimethalin, oxyfluorfen + prodiamine, and trifluralin + isoxaben were evaluated, along with spray-applied formulations of dimethenamid, indaziflam, and prodiamine + isoxaben. Flumioxazin consistently provided over 90% control of praxelis at both sites. Indaziflam control was inconsistent between the two sites, providing 100% control in Apopka but only a 22% reduction in weed counts in Balm. Oxyfluorfen + pendimethalin, oxyfluorfen + prodiamine, and prodiamine + isoxaben also provided control (57% to 97% reduction in shoot weight), albeit generally to a lesser degree than was observed with flumioxazin. All PRE herbicides provided similar control of both praxelis and bluemink, with the exception of dimethenamid and dimethenamid + pendimethalin, which reduced bluemink shoot weight more than praxelis. Clopyralid, glyphosate, and triclopyr all provided effective POST control of mature and flowering praxelis through 12 wk after treatment (WAT) and resulted in greater praxelis control than glufosinate. Results suggest that many commonly used PRE and POST herbicides would provide control of praxelis, but use of PRE and POST herbicides as well as sequential applications may be needed for long-term management.

Greenhouse and outdoor container experiments were conducted to determine garden spurge and large crabgrass emergence when seeds were placed either on top of or below three different mulch materials [pine bark (PB), hardwood (HW), or pine straw (PS)] applied at five depths (0, 1.3, 2.5, 5.1, and 10.2 cm). To elucidate mulch characteristics that contributed to weed control, photosynthetic active radiation (PAR) was recorded underneath each mulch layer, moisture retention was monitored for 24 h following irrigation, and particle size was determined using standard soil sieves. HW reduced PAR (97%) more than did PB (90%) or PS (92%) at 1.3 cm, but few or no differences were noted between mulches at greater mulch depths. HW also contained the highest percentage of small particles and consequently retained more water (29%), than PB (14%) or PS (22%) 24 h following a simulated irrigation event. Emergence of large crabgrass and garden spurge was consistently greater when seeds were placed on top of the mulch, compared to seeds placed below. Emergence of both species also tended to respond to increasing depth in a quadratic manner, indicating that once a critical level of mulch was applied (2.5 to 5 cm), further reductions in weed emergence would not be observed, at least over the short term (12 wk). PB and PS tended to provide a greater reduction in emergence of both species compared to HW. This research also indicates that larger particle materials such as PB or PS would be advantageous because of their ability to suppress weed emergence regardless of seed position.

Skunk-vine (Paederia foetidaL.) is an invasive vine native to eastern and southern Asia and is widely distributed in Florida, Hawaii, and other southeastern U.S. states; however, little research has focused on herbicide control. Greenhouse and field experiments were conducted to determine efficacy of aminocyclopyrachlor, aminopyralid, fluroxypyr, glyphosate, imazapic, triclopyr amine, and triclopyr ester at low and high labeled rates when foliar applied toP. foetidaat various growth stages in greenhouse experiments. Longer-term control was evaluated in field experiments in central Florida using the same herbicides. PRE herbicides labeled for use in landscape plantings, including dimethenamid-P, flumioxazin, indaziflam, isoxaben, and prodiamine, were also evaluated in greenhouse trials by seeding containers withP. foetidaseed. In greenhouse experiments, POST herbicides, including aminocyclopyrachlor, aminopyralid, glyphosate, both triclopyr formulations, and the high rate of fluroxypyr (0.24 kg ae ha−1), provided >90% control across all growth stages at 4 mo after treatment with no regrowth observed. Imazapic provided 49% to 89% control, with efficacy decreasing withP. foetidasize, and generally provided less control than other treatments. Field experiments confirmed results from greenhouse studies. In PRE trials, flumioxazin and prodiamine provided better control than all other PRE herbicides evaluated, reducing shoot weights by 99% and 84%, respectively, compared with nontreated controls. Our data suggest all herbicides evaluated POST could potentially be used to manageP. foetida, although less control was achieved with imazapic compared with other herbicides. Further research is needed to determine herbicide efficacy on more mature plants and to develop application methods that would be less injurious to non-target vegetation. In landscapes, flumioxazin or prodiamine could be used for PRE control, but POST options that are labeled for landscape use should be identified in future research.

Research objectives were to determine the effect of fertilization method (incorporation, subdress, and topdress) on weed growth and the performance of preemergence herbicides applied to soilless substrates. Nursery containers were filled with a pine bark:peat substrate and fertilized at two different rates [4.4 and 9.5 kg.m−3 (8.9 and 19.2 lb.yd−3)] via topdressing, subdressing, or incorporating. Containers were treated with either dimethenamid-P for spotted spurge (Euphorbia maculata L.), flumioxazin for eclipta (Eclipta prostrata L.) or prodiamine for large crabgrass (Digitaria sanguinalis L.). A control was established for each fertilizer rate/placement and weed species that was not treated. Incorporating or subdressing fertilizer resulted in reduced large crabgrass and spotted spurge growth in non-treated containers. Weeds grew larger at the higher fertility rates in both topdress and incorporated treatments but fertilizer rate did not affect growth of spotted spurge or large crabgrass when fertilizers were subdressed. Herbicides generally provided commercially acceptable weed control regardless of fertilizer treatment, but results varied with species. Results suggest that in the absence of herbicides, topdressing may result in greater weed growth compared with subdressing or incorporating fertilizers; however, fertilizer placement will have less impact on herbicide performance if proper herbicides are chosen and applied correctly.Index words: topdress, subdress, incorporate, large crabgrass, eclipta, spotted spurge, preemergenceChemicals used in this study: Flumioxazin (SureGuard®); 2-[7-fluoro-3,4-dihydro-3-oxo-4-(2-propynyl)-2H-1,4-benzoxazin-6-yl]-4,5,6,7-tetrahydro-1H-isoindole1,3(2H)-dione; Dimethenamid-P (Tower) 2-chloro-N-[(2,4-dimethyl-3-thienyl)-N-(2-methoxy-1-methylethyl)acetamide; Prodiamine (Barricade) 2,4-dinitro-N3, N3-dipropyl-6-(trifluoromethyl)-1,3-benzenediamine (Barricade®)Species used in this study: Large crabgrass (Digitaria sanguinalis L.); Eclipta (Eclipta prostrata L.); Spotted spurge (Euphorbia maculata L.)

The objective of this research was to evaluate dithiopyr and isoxaben combinations and indaziflam (Marengo) for early postemergence control of woodland bittercress (Cardamine flexuosa) and yellow woodsorrel at 4 different early growth stages. Herbicides evaluated included sprayable formulations of isoxaben, dithiopyr + isoxaben, dithiopyr, indaziflam, and prodiamine + isoxaben without any surfactants. Woodland bittercress growth stages included seed production (extra-large), recently flowered (large), 6 to 9 leaf (medium) or in 2 to 5 leaf stage (small), while yellow woodsorrel growth stages included 8 to 12 leaf stage (extra-large), 4 to 6 leaf stage (large), 2 to 4 leaf stage (medium) and cotyledon to 1 leaf stage (small). Shoot fresh weight data showed all treatments provided ≤98% of woodland bittercress at the small stage. Dithiopyr + isoxaben (98%), isoxaben (90%), and indaziflam (93%) provided the highest level of woodland bittercress control at the medium stage and were the only treatments providing acceptable control (≥80%). In the large stage, dithiopyr + isoxaben provided acceptable control (80%) and outperformed other treatments. All treatments with the exception of isoxaben generally provided acceptable control of yellow woodsorrel up to the large growth stage. Only indaziflam (86% control) provided acceptable control at the extra-large stage. Index words: herbicide, postemergence weed control, container-grown plants, phytotoxic damages. Herbicides used in this study: isoxaben (Gallery® 4SC) N-[3-(1-ethyl-1-methylpropyl)- 5-isoxazolyl]-2,6-dimethoxybenzamide; dithiopyr (Dimension® 2EW) S,S'-dimethyl 2-(difluoromethyl)-4- (2-methylpropyl)-6-(trifluoromethyl)- 3,5-pyridinedicarbothioate; indaziflam (Specticle® FLO) N-[(1R,2S)-2,3-dihydro-2,6-dimethyl-1H-inden-1-yl]-6-(1-fluoroethyl)-1,3,5-triazine-2,4-diamine; prodiamine + isoxaben (Gemini® SC) 2,4-dinitro-N3,N3-dipropyl-6-(trifluoromethyl)-1,3-benzenediamine + N-[3-(1-ethyl-1-methylpropyl)- 5-isoxazolyl]-2,6-dimethoxybenzamide; dithiopyr + isoxaben (Dimension® + Gallery®) S,S'-dimethyl 2-(difluoromethyl)-4- (2-methylpropyl)-6-(trifluoromethyl)- 3,5-pyridinedicarbothioate + N-[3-(1-ethyl-1-methylpropyl)- 5-isoxazolyl]-2,6-dimethoxybenzamide. Weed species evaluated: woodland bittercress (flexuous bittercress) (Cardamine flexuosa With.); yellow woodsorrel (Oxalis stricta L.).

Artilleryweed is an annual or short-lived perennial weed that is becoming increasingly problematic in nurseries and landscapes in tropical and subtropical environments. Currently, no herbicide recommendations exist for management of artilleryweed. Objectives of this trial were to evaluate PRE and POST herbicides for efficacy on artilleryweed. All studies were conducted in Apopka, FL in a shaded greenhouse. Herbicides evaluated for POST control included diquat, dimethenamid-P, flumioxazin, glufosinate, glyphosate, indaziflam, oxadiazon, pelargonic acid, sulfentrazone and sulfosulfuron applied at their highest labelled rates to mature (10 to 12 cm height) artilleryweed. For PRE experiments, pots were overseeded with artilleryweed seed and treated with dimethenamid-P, indaziflam, isoxaben, oxadiazon, oxyfluorfen+prodiamine, oxyfluorfen+pendimethalin, pendimethalin, pendimethalin+dimethenamid-P, prodiamine, prodiamine+isoxaben, S-metolachlor, or trifluralin+isoxaben. When assessing both initial fresh weight and regrowth, flumioxazin and glufosinate provided the most consistent POST control when applied at the highest labelled rate, although regrowth did occur following application with glufosinate. All PRE herbicides evaluated provided over 90% control of artilleryweed with the exception of isoxaben and trifluralin+isoxaben. Results indicate that several effective options exist for artilleryweed management, but more effective control will likely be achieved when herbicides are applied PRE.

Although primarily used as an effective PRE herbicide, indaziflam has been shown to provide early POST control of some weeds commonly found in nursery production. Previous investigation on the early POST efficacy of indaziflam focused on the liquid formulation, and the ability of the granular formulation to provide early POST weed control is unknown. Nursery trials were conducted to evaluate early POST control of oxalis using two formulations of indaziflam. Oxalis seeds were surface sown to nursery containers at two separate dates and grown until they reached the two- to four-leaf stage (2-4L) and six- to eight-leaf stage. Both growth stages were treated with indaziflam at 12.6, 25.1, 50.2, and 100.4 g ai ha−1using either a granular (G) or liquid (SC) formulation. A chemical control treatment (glyphosate) and a nontreated control were also included for comparison. The SC formulation provided > 90% control of both oxalis growth stages at all four rates and was similar to glyphosate. The G formulation at 12.6 and 25.1 g ha−1only provided marginal control, but overall performed similarly to the SC formulation at the 50.2 and 100.4 g ha−1rate in most experiments. In contrast to the SC formulation, the G formulation is labeled for use over the top of container-grown nursery crops. Results of this research indicate that in areas where oxalis is the primary weed of concern, the G formulation of indaziflam could be applied to control small oxalis up to the 2-4L stage at the currently labeled rate (50.2 g ha−1).

Use of organic mulch is one of the most common methods of weed control in landscape planting beds and provides other benefits, including improved soil characteristics, increased growth of ornamental plants, and enhanced property aesthetics. In the landscape maintenance industry, it is common to apply mulch and herbicides concurrently to landscape beds to provide long-term, broad-spectrum weed control. It is known that herbicides behave differently when applied to different soil types and organic materials; however, research is lacking concerning which herbicides are most effective with different mulch materials in the landscape. Determining the most effective herbicide–mulch combinations could potentially improve weed control, reduce labor costs from hand weeding, and mitigate negative environmental impacts resulting from off-site herbicide movement. The objective of this paper is to review the research that has been conducted pertaining to various mulch–herbicide combinations in the landscape and in other areas of agricultural production while also identifying key knowledge gaps that should be addressed in future research. Review of the literature suggests satisfactory weed control can be achieved with high mulch depths (≥ 7 cm) regardless of herbicide use, and herbicide–mulch interactions become more pronounced as mulch depth decreases. Additionally, future research is needed to determine which herbicides are best suited for different mulch types to improve weed control and potentially reduce environmental impacts, including herbicide leaching and runoff into urban and suburban waterbodies.

Three experiments were conducted to evaluate early POST control of yellow woodsorrel using PRE-applied herbicides. In experiment 1, yellow woodsorrel was seeded at two dates in a commercial pine-bark substrate and grown until reaching either the cotyledon–one-leaf (C-1L) or two- to four-leaf (2-4L) growth stage. The herbicides isoxaben, indaziflam, and dimethenamid-p were applied at these growth stages. Two rates of isoxaben and indaziflam provided yellow woodsorrel control (≥ 80% reduction in fresh weight [FW]) when applied at the C-1L stage; however, once yellow woodsorrel reached the 2-4L stage, indaziflam was the only herbicide that provided effective control at both rates tested. Experiments 2 and 3 were similar to experiment 1, except two labeled rates of dithiopyr were also evaluated. In experiment 2, all herbicides evaluated provided ≥ 90% reduction in FW of yellow woodsorrel at the C-1L stage. Although no differences in FW were observed among any of the herbicide treatments when yellow woodsorrel were treated at the 2-4L stage, control ratings indicated that indaziflam provided the most effective yellow woodsorrel control. Experiment 3 results also indicated that isoxaben, indaziflam, and dithiopyr controlled yellow woodsorrel (≥ 95% reduction in FW) when treatments were applied at the C-1L stage, whereas dimethenamid-p reduced shoot FW 70%. When yellow woodsorrel was treated after reaching the 2-4L stage, indaziflam provided the greatest control of any herbicide evaluated.

Three woody shrub species [cleyera (Ternstroemia gymnanthera Thunb. ‘Conthery’), Indian hawthorn (Rhaphiolepis indica L.) and loropetalum (Loropetalum chinensis Oliv.‘Ruby’)] were container-grown for one growing season in 2008 using either pinebark (industry standard), clean chip residual or WholeTree (derived by-products from the forestry industry) as potting substrates and then transplanted into the landscape in 2008. An Automated Carbon Efflux System was used to continually monitor soil CO2 efflux from December 2010 through November 2011 in each species and substrate combination. Changes in soil carbon (C) levels as a result of potting substrate were assessed through soil sampling in 2009 and 2011 and plant biomass was determined at study conclusion. Results showed that soil CO2-C efflux was similar among all species and substrates, with few main effects of species or substrate observed throughout the study. Soil analysis showed that plots with pinebark contained higher levels of soil C in both 2009 and 2011, suggesting that pinebark decomposes slower than clean chip residual or WholeTree and consequently has greater C storage potential than the two alternative substrates. Results showed a net C gain for all species and substrate combinations; however, plants grown in pinebark had greater C sequestration potential.