Annual bluegrass is one of the most problematic weeds in the turfgrass industry, exhibiting both cross-resistance and multiple-herbicide resistance. Prodiamine, pronamide, and indaziflam are commonly used preemergence herbicides for the control of this species on golf courses in the southern United States. There have been increasing anecdotal reports of annual bluegrass populations escaping control with these herbicides, but resistance has yet to be confirmed. To evaluate the response of annual bluegrass to three herbicides, populations were collected from golf courses, athletic fields, and landscape areas in Texas and Florida, and a dose-response assay was conducted on populations that were suspected to be resistant to and known to be susceptible to prodiamine, pronamide, and indaziflam. The suspected-resistant populations showed survival to prodiamine at 32 times the recommended field rate (both populations from Florida and Texas) of 736 g ai ha−1, and to pronamide at 32 times (the Florida populations) or 16 times (the Texas populations) the recommended field rate of 1,156 g ha−1. In contrast, the known susceptible populations attained 100% mortality at rates as low as 46 and 578 g ha−1, respectively, from applications of prodiamine and pronamide. For indaziflam, the suspected-resistant populations showed reduced sensitivity up to the recommended field rate of 55 g ha−1, but they were controlled when treated with a rate twice that of the field rate. Overall, annual bluegrass populations with resistance to prodiamine and pronamide, and reduced sensitivity to indaziflam (at the recommended field rate) were confirmed from golf courses in Florida and Texas. In the presence of herbicide-resistant annual bluegrass populations, especially to commonly used herbicides such as prodiamine and pronamide, turfgrass managers should adopt integrated management strategies and frequently rotate herbicide sites of action, rather than relying solely on microtubule-assembly inhibitors or cellulose biosynthesis inhibitors, to control this species.

The mitotic-inhibiting herbicide pronamide controls susceptible annual bluegrass (Poa annua L.) pre- and postemergence, but in some resistant populations, postemergence activity is compromised, hypothetically due to a target-site mutation, lack of root uptake, or an unknown resistance mechanism. Three suspected pronamide-resistant (LH-R, SC-R, and SL-R) and two pronamide-susceptible (BS-S and HH-S) populations were collected from Mississippi golf courses. Dose–response experiments were conducted to confirm and quantify pronamide resistance, as well as resistance to flazasulfuron and simazine. Target sites known to confer resistance to mitotic-inhibiting herbicides were sequenced, as were target sites for herbicides inhibiting acetolactate synthase (ALS) and photosystem II (PSII). Pronamide absorption and translocation were investigated following foliar and soil applications. Dose–response experiments confirmed pronamide resistance of LH-R, SC-R, and SL-R populations, as well as instances of multiple resistance to ALS- and PSII-inhibiting herbicides. Sequencing of the α-tubulin gene confirmed the presence of a mutation that substituted isoleucine for threonine at position 239 (Thr-239-Ile) in LH-R, SC-R, SL-R, and BS-S populations. Foliar application experiments failed to identify differences in pronamide absorption and translocation between the five populations, regardless of harvest time. All populations had limited basipetal translocation—only 3% to 13% of the absorbed pronamide—across harvest times. Soil application experiments revealed that pronamide translocation was similar between SC-R, SL-R, and both susceptible populations across harvest times. The LH-R population translocated less soil-applied pronamide than susceptible populations at 24, 72, and 168 h after treatment, suggesting that reduced acropetal translocation may contribute to pronamide resistance. This study reports three new pronamide-resistant populations, two of which are resistant to two modes of action (MOAs), and one of which is resistant to three MOAs. Results suggest that both target site– and translocation-based mechanisms may be associated with pronamide resistance. Further research is needed to confirm the link between pronamide resistance and the Thr-239-Ile mutation of the α-tubulin gene.

Weeds are difficult to control in potted tropical ornamentals, especially when plants are kept for extended time periods at a nursery. Management is complicated by the lack of tolerance data for many tropical species. Experiments were conducted in 2015, 2016, and 2017 at the Gulf Coast Research and Education Center in Balm, FL, to evaluate tolerance of stromanthe, croton, philodendron, arbicola, cordyline, ixora, plumbago, allamanda, bird-of-paradise, firebush, and hibiscus to granular applications of indaziflam, flumioxazin, pendimethalin + oxyfluorfen, pendimethalin + dimethenamid-P, trifluralin + oxyfluorfen + isoxaben, and trifluralin + isoxaben, and liquid applications of prodiamine + isoxaben and dimethenamid-P. Indaziflam, pendimethalin + oxyfluorfen, and trifluralin + oxyfluorfen + isoxabin were safe for use on all evaluated ornamentals except stromanthe. Dimethenamid-P and pendimethalin + oxyfluorfen were safe on all evaluated ornamentals except allamanda. Flumioxazin damaged philodendron and bird-of-paradise but was safe on all other ornamentals tested. Trifluralin + isoxaben and prodiamine + isoxaben were safe on hibiscus, firebush, and bird-of-paradise, but prodiamine + isoxaben damaged allamanda. We have identified multiple PRE herbicides that can safely be used on multiple tropical ornamentals grown in containers.

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.

Prodiamine is a dinitroaniline herbicide labeled for PRE control of goosegrass in warm- and cool-season turfgrass. In 2013, several golf course roughs in Maryville, TN reported poor goosegrass control (< 20%) following prodiamine treatment at 1,120 g ai ha-1. We harvested suspected prodiamine-resistant (PR) and prodiamine-susceptible (S) goosegrass phenotypes from the field and exposed them to a range of increasing prodiamine concentrations in hydroponic culture. Exposure to prodiamine at 0.001 mM reduced root growth of the S phenotype to 11% of the non-treated check. By comparison, exposure to 0.001 mM prodiamine had minimal effect on the PR phenotype, as root growth was 94% of the non-treated check. Molecular analyses revealed that PR plants contained a threonine (Thr) to isoleucine (Ile) substitution at position 239 on the α-tubulin 1 (TUA1) protein. The substitution, found in all PR plants, is the mechanism of prodiamine resistance in this phenotype. In field studies, topramezone controlled PR goosegrass 72% to 89% by 50 d after treatment (DAT) compared to only 22% to 23% for foramsulfuron. Topramezone treatment injured bermudagrass 34% to 60% from 7 to 14 DAT; however, injury was≤6% 28 DAT and 0% by the end of the study. Our results indicate that POST applications of topramezone can control dinitroaniline-resistant goosegrass. In addition, we established an easy-to-use genotyping assay to quickly screen goosegrass phenotypes for a target-site mutation (Thr-239-Ile) on TUA1 associated with resistance to dinitroaniline herbicides such as prodiamine. Future research should work to expand this assay for use with other weed species and herbicidal modes of action.

Diuron, fluorochloridone, hexazinone, metribuzin, norflurazon, oryzalin, prodiamine, simazine, and terbacil controlled seedling asparagus planted in sprinkler-irrigated plots similarly (>89%). In furrow-irrigated plots, cinmethylin, diuron, fluorochloridone, hexazinone, napropamide, oryzalin, and prodiamine provided similar control (>86%) of planted seedling asparagus. Herbicides with high water solubilities that depended upon root uptake for maximum activity tended to control seedling asparagus better in sprinkler-irrigated tests than in furrow-irrigated tests. Fluorochloridone, norflurazon, and prodiamine provided partial control of volunteer asparagus (48 to 84%) in an established stand of furrow-irrigated asparagus.

Studies were conducted to determine the effects of tillage level on weed control and yield of asparagus grown on a sandy loam soil under sprinkler irrigation. Without herbicides, horseweed and kochia populations increased in no-till asparagus production over a 3-yr period, compared to asparagus that was rototilled either once in the spring or once in the spring and again at layby. Without herbicides, hairy nightshade populations increased most when asparagus was rototilled both in the spring and at layby. Volunteer asparagus was controlled best when herbicides and tillage were combined in the spring and again at layby. Common groundsel was controlled without herbicides by rototilling both in the spring and at layby. Diuron at 1.4 kg ai/ha plus prodiamine at 1.4 kg/ha or metribuzin at 0.9 kg/ha plus norflurazon at 2 kg/ha controlled all weeds under all three tillage levels when split-applied in the spring and at layby. Tillage level had no effect on total asparagus spear number or weight if tillage was performed in mid March before asparagus emergence.

Green kyllinga is a relatively new weed species in well-irrigated turfs in the southwest US. To understand the germination requirements of green kyllinga, the effects of planting depth, temperature, pH, and osmotic potential were determined. Green kyllinga emergence was sensitive to planting depth. At 21 days after planting (DAP), emergence of green kyllinga was 60% when planted at the soil surface but only 20% at 0.5 cm and less than 5% at 1 cm. Germination occurred at temperatures between 17 and 30 C but was notably better between 20 and 24 C. Germination was uniform from pH 5.5 to 9.5. Germination decreased between the water potentials −0.1 to −0.6 MPa, although germination was high at water potentials found in irrigated turf. The environmental conditions found in nonstressed turf areas in Arizona will likely support the establishment of green kyllinga. The efficacy of herbicides for the control of green kyllinga was also determined. Control of kyllinga (95% or greater) was obtained with preemergence applications of oxadiazon, dithiopyr, and metolachlor, and with postemergence applications of DSMA, halosulfuron-methyl, and imazaquin.

Control of goosegrass and large crabgrass with different preemergence herbicides for the initial and sequential application was studied at four locations in Indiana. Pendimethalin at 1.1 kg ai ha-1 was used as the initial application in all treatments. Sequential treatments applied 6 wk after the initial treatment consisted of: 2.2 kg ha-1 benefin; 1.4/0.7 kg ha-1 benefin/trifluralin; 8.4 kg ha-1 bensulide; 11.8 kg ha-1 DCPA; 0.6 kg ha-1 dithiopyr; 2.2 kg ha-1 oxadiazon; 1.1 kg ha-1 pendimethalin; or 0.6 kg ha-1 prodiamine. Dithiopyr at 0.6 kg ha-1 with no initial application was also included. Highest large crabgrass control ratings were obtained through September with pendimethalin + pendimethalin, pendimethalin + dithiopyr, and dithiopyr alone postemergence. All other sequential applications tested improved control over a single application of 1.1 kg ha-1 pendimethalin, but rarely gave adequate season long control.

The influence of PRE herbicides on rooting characteristics of bermudagrass turfgrass was studied using sod plugs removed from the field. Greenhouse root fresh weight was reduced the greatest with dithiopyr or prodiamine. Pendimethalin caused fewer fresh weight reductions compared to dithiopyr or prodiamine and these reductions were usually for a short period. Root weight loss was due to lower root density and root malformation. Significant numbers of malformed roots were also observed for greater periods of time where dithiopyr or prodiamine had been applied.

PRE and POST herbicides were evaluated for their effects on root growth of Kentucky bluegrass and tall fescue turf. All PRE treatments, bensulide at 14.0 kg ai ha−1, DCPA at 11.8 kg ha−1, dithiopyr at 0.4 kg ha−1, pendimethalin at 1.7 kg ha−1, and prodiamine at 0.6 kg ha−1, inhibited root growth when cores, 10 cm in diam and 2.5 cm deep, of herbicide-treated Kentucky bluegrass were placed into pots of perlite. Only prodiamine inhibited tall fescue rooting. None of the PRE treatments reduced rooting of grasses when 10-cm diam and 16-cm deep cores were sampled from the field. No differences in rooting were observed among any of the POST treatments on either species.

For effective full-season control of dodder in alfalfa produced for seed, herbicides applied to soil in late winter or early spring should remain active through June. Pendimethalin or prodiamine at 2.2 kg ai ha-1 applied in mid March controlled 97 to 100% of dodder through May and 92 to 100% through June. At 3.4 kg ha-1, both controlled 96 to 100% of dodder through June each year, and control of 95 or 96% persisted through July in 1 of 3 yr. In the greenhouse, trifluralin was only about 1/8 as active against dodder as pendimethalin and prodiamine. In the field, trifluralin at 2.2 kg ai ha-1 controlled dodder satisfactorily through May in 3 of 4 yr and through June in 1 of 4 yr. At 4.5 kg ha-1, trifluralin controlled 99% of dodder through May in each of 3 yr; control was satisfactory through June in 2 of 3 yr. Oryzalin was less effective than the other three dinitroaniline herbicides. A standard herbicide, chlorpropham at 6.7 kg ai ha-1, controlled 97 to 100% of dodder through May, but control usually did not persist through June. Another standard herbicide, DCPA at 11.2 kg ai ha-1, controlled 97 or 98% of dodder through June in 2 of 3 yr. Pendimethalin and prodiamine at 3.4 and 6.7 kg ai ha-1 did not affect the yield or quality of seed produced by established alfalfa. Heavy sprinkler irrigation (15 cm of water) after application did not diminish dodder control from pendimethalin or prodiamine.

The efficacy of two applications of several PRE herbicides for extended control of long-stalked phyllanthus and leafflower were evaluated under container nursery conditions at two climatically different sites in Florida. Prodiamine at 4.5 kg ai/ha provided the longest and most consistent reductions in number, percent coverage (visual) of the medium, and dry weight of both species. Ten weeks of excellent PRE control (percent medium coverage ≤ 10%; number of weeds reduced by ≥ 70%) of both species was obtained at one site after the first and second applications of prodiamine at 2.2 or 4.5 kg ai/ha; two applications were required at the second site for similar control. Rates of the other herbicides were generally too low for excellent control of both species after one application, the exceptions being dithiopyr at 4.5 kg ai/ha and the preformulated combination of isoxaben and oryzalin (1.1 and 3.4 kg ai/ha, respectively). These herbicides provided good (10% < percent medium coverage ≤ 20%; number of weeds reduced by ≥ 70%) to excellent PRE control of long-stalked phyllanthus after the first and second applications at one site. Percent coverage of the medium by either species in untreated containers was 96 to 100%.

Poor annual bluegrass control was reported in golf course roughs following treatment with prodiamine (1120 gaiha−1) and glyphosate (840 gaeha−1) during hybrid bermudagrass dormancy. Research was conducted to determine if this annual bluegrass phenotype was resistant to both prodiamine and glyphosate and to determine the efficacy of herbicide mixtures for controlling this phenotype in the field. In PRE or POST dose-response experiments, 9 to 31 times more prodiamine or glyphosate was needed to control (or reduce dry biomass of) this resistant phenotype by 50% compared to an herbicide-susceptible phenotype. Moreover, glyphosate-susceptible plants accumulated 50% more shikimic acid (898 mgkg−1) 6 d after treatment than those resistant to glyphosate (394 mgkg−1). October (fall) applications of herbicide mixtures containing trifloxysulfuron, simazine, S-metolachlor, or mesotrione controlled this resistant annual bluegrass phenotype 84 to 98% in April (spring), with no differences detected among treatments. Our findings document the second instance of annual bluegrass evolving multiple resistance in a managed turfgrass system. However, several herbicide mixtures can be used to effectively manage this resistant phenotype.

Annual, cylindric, and globe sedges were controlled > 90% with a single application of MSMA at 2.2 kg ai/ha in field studies. But this same treatment controlled fragrant and green kyllingas only 69 and 52%, respectively. Control was increased to 82 and 81%, respectively, with a repeat application. Other postemergence-applied (POST) herbicides evaluated included bentazon, halosulfuron, imazapic, imazaquin, and CGA-362622. Postemergence-applied herbicides were applied either once or twice, as well as alone and in combination with MSMA. In general, a sequential application of MSMA, either alone or in combination with any of the aforementioned herbicides, except bentazon, provided maximum control of the sedge and kyllinga species evaluated. Preemergence-applied (PRE) oxadiazon and S-metolachlor, controlled annual sedge ≥ 94% at 7 wk after treatment (WAT) in field studies and 96 and 70% at 9 WAT, respectively. Dithiopyr and prodiamine provided 86 to 80% control of annual sedge over the 9-wk rating period. In a hydroponic-type laboratory study, oxadiazon and S-metolachlor were more effective than atrazine, bensulide, imazaquin, oryzalin, or simazine, in reducing seedling development of annual, cylindric, and globe sedges, and green kyllinga.

Both prodiamine and flumioxazin are used in the nursery production and landscape maintenance industries in the southeastern United States for preemergence weed control. Research was conducted to determine whether a tank mixture of these two herbicides would be more effective than either component applied alone. Prodiamine alone, flumioxazin alone, and a 72 : 28 (by weight) prodiamine–flumioxazin mixture were each applied at a series of rates to containers filled with a pine bark–sand substrate that is typical for nursery production in the southeastern United States. Our intent was to have a rate range that hopefully extended from ineffective to lethal for each treatment series. Subsequent to treatment, containers were overseeded with either large crabgrass, spotted spurge, or eclipta. Percent control was determined by comparing treated weed foliage fresh weight to that of the appropriate nontreated control at 6 and 12 wk after application. ANOVA followed by nonlinear regression was used to evaluate the interaction of prodiamine and flumioxazin when combined and to determine the rate of each treatment series required for 95% control (if applicable) for each of the three weed species. Results varied with weed species. The mixture was synergistic and more cost effective than either of the components applied alone in controlling spotted spurge. With respect to large crabgrass control, the mixture was additive and slightly more cost effective than the components. Eclipta could only be controlled with flumioxazin, and this control was antagonized by the addition of prodiamine.

Goosegrass is a problematic weed in turfgrass, and overuse of dinitroaniline (dna) herbicides has resulted in evolution of resistant populations. The objectives of this research were to (1) evaluate responses of a susceptible (S) goosegrass compared to a suspected resistant (R) biotype from Griffin, GA to prodiamine, and (2) evaluate efficacy of various PRE herbicides for control. Prodiamine rates required for 50% control and 50% shoot reductions after 6 wk for R-goosegrass measured > 13.44 and 3.2 kg ai ha−1, respectively, whereas rates for the S-population measured 0.45 and < 0.42 kg ha−1, respectively. In field experiments, sequential applications of dithiopyr and prodiamine provided < 20% control of R-goosegrass over 2 yr. Single applications of dimethenamid-P at 1.68 kg ai ha−1 provided < 50% goosegrass control in 2011 but provided excellent control (≥ 90%) at 7 mo after initial treatments (MAIT) in 2012. Single and sequential applications of indaziflam provided excellent control of goosegrass in both years, and oxadiazon controlled goosegrass > 85% at 7 MAIT in 2011 and ≥ 90% in 2012. Single and sequential PRE sulfentrazone applications controlled goosegrass < 60% in 2011 but averaged 94% control in 2012. Overall, indaziflam and oxadiazon provided good (80 to 89%) to excellent control of dna-resistant goosegrass in both years, but dimethenamid and sulfentrazone were inconsistent.

Annual bluegrass control was reduced following 7 yr of continuous fall application of dinitroaniline (DNA) herbicides. Annual bluegrass control was < 40% on two fairways in year eight following prodiamine applied at 1.1 kg ai ha−1. In dose–response studies conducted in growth chambers, this annual bluegrass population exhibited 105-fold resistance in shoot growth to prodiamine compared with a known susceptible population. A 6.4-fold resistance to prodiamine was found when comparing annual bluegrass root growth to the known susceptible biotype. Spring-applied oxadiazon did not affect shoot or root growth between annual bluegrass biotypes. Equivalent levels of control were attained with pronamide. The presence of DNA-resistant annual bluegrass, in addition to previously confirmed triazine-resistant biotypes on North Carolina golf courses, indicates a need for resistance management strategies to be integrated into golf turf management practices.

Amicarbazone and indaziflam are relatively new herbicides that provide effective control of important weed species in turfgrass. A concern for golf course superintendents and turfgrass managers is the lack of information about runoff risk of these two herbicides, which is a limitation to their proper and safe use. The objectives of this research were (1) to compare lateral movement in surface soil of amicarbazone and indaziflam to other commonly used PRE herbicides in turfgrass (i.e., dithiopyr, prodiamine, pronamide, simazine) and (2) to determine whether incorporating the herbicide with irrigation before a simulated storm event reduces lateral movement. Herbicides were applied at full label rates in two locations (Jay and Milton, FL) with 14% slope, and lateral movement was evaluated using perennial ryegrass and annual bluegrass as bioindicators. Incorporating PRE herbicides with irrigation a few hours before a major simulated storm event did not reduce lateral movement of any of the herbicides evaluated. All herbicides moved outside the treated area regardless of the presence of a simulated storm event. Herbicide lateral movement varied from 61 to 153 cm in Jay, and from 5 to 103 cm in Milton. The Milton location had higher sand content and lower organic matter content than Jay, which favored water infiltration. No herbicide effects were observed 210 cm downslope from the treated area. On the basis of our results, the ranking from highest to lowest lateral movement was pronamide > simazine ≥ indaziflam > amicarbazone ≥ dithiopyr > prodiamine. The difference in lateral movement was approximately 60 to 80 cm between pronamide and prodiamine depending on location and evaluation timing for the 14% slope at the study sites. The results of the present study provide guidance for golf course superintendents and turfgrass managers to determine buffer zones in sensitive areas.

Preemergence (PRE) herbicides may affect the ability to reestablish warm-season turfgrasses in winter-injured areas. Experiments were conducted in 1996 and 1997 to evaluate the effects of fall or spring applications of six PRE herbicides on the vegetative establishment of Tifway bermudagrass, and Meyer and El Toro zoysiagrass. PRE herbicides were applied at the recommended rates during the fall of 1995 and 1996 and at recommended or reduced rates during the spring of 1996 and 1997. Oxadiazon, benefin plus trifluralin, or oryzalin did not inhibit Tifway bermudagrass or zoysiagrass sprig establishment. Fall applications of prodiamine and dithiopyr at full rates suppressed Tifway bermudagrass establishment as much as 25%, but recovery was evident by the end of the growing season. Reduced spring rates of prodiamine diminished its suppressive effects on Tifway establishment. Zoysiagrass establishment was suppressed as much as 20% by full or reduced rates of prodiamine but was less affected by dithiopyr. Pendimethalin had lesser and briefer suppressive effects than prodiamine and dithiopyr had on either species. Results suggested that avoidance of or reduced rates of prodiamine or dithiopyr may be warranted in areas prone to winter injury.