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Mugwort (Artemisia vulgaris) is a perennial invasive weed species that has infiltrated row crops, turfgrass, ornamentals, and various noncrop areas. Currently, multiple mimics of indole-3-acetic acid can provide control of this species; however, these herbicides can damage certain sensitive ornamental plants. When applied at reduced rates, the p-hydroxyphenylpyruvate dioxygenase (HPPD)-inhibiting herbicides mesotrione and topramezone have demonstrated some selectivity among certain ornamental plants. Field and greenhouse studies were initiated to evaluate whether these herbicides could control mugwort when applied alone, or in mixtures with photosystem II (PSII)-inhibiting herbicides that often provide synergistic weed control. In the field, mesotrione controlled mugwort between 30% and 60% by 21 days after treatment when applied at 0.093 to 0.187 lb/acre. When the PSII-inhibiting herbicide atrazine was added, control increased to 78% and 79%. In the greenhouse, similar rates produced greater control in mugwort, and all mesotrione treatments limited mugwort regrowth by at least 95% when compared with untreated control. When HPPD inhibitor rates were reduced further, the addition of the PSII inhibitors atrazine or bentazon was not sufficient at providing acceptable control of mugwort.

Star-of-bethlehem (Ornithogalum umbellatum) commonly invades turfgrass stands throughout the transition zone. Field experiments were conducted to evaluate sulfentrazone and mixtures of mesotrione and topramezone with bromoxynil and bentazon for selective star-of-bethlehem control in cool-season turf. At 4 weeks after treatment (WAT), applications of sulfentrazone at 0.25 and 0.38 lb/acre provided >95% control of star-of-bethlehem in 2008 and 2009. Star-of-bethlehem control following applications of commercial prepackaged mixtures containing sulfentrazone was not significantly different from applications of sulfentrazone alone, at either rate, at 4 WAT in 2008 and 2009. Control with carfentrazone-ethyl at 0.03 lb/acre measured to <75% at 4 WAT each year. Star-of-bethlehem control at 2, 3, and 4 WAT with topramezone at 0.033 lb/acre was increased by 77%, 50%, and 46%, respectively, from the addition of bromoxynil at 0.50 lb/acre. Similarly, the inclusion of bromoxynil at 0.50 lb/acre increased the level of control observed following treatment with mesotrione at 0.28 lb/acre by 77%, 30%, and 32% at 2, 3, and 4 WAT. These data suggest that sulfentrazone and mixtures of topramezone and mesotrione with bromoxynil can be used to provide postemergence control of star-of-bethlehem in cool-season turf.

Field and greenhouse studies were conducted to determine if two indole-3-acetic acid herbicide mimics, aminopyralid and aminocyclopyrachlor-methyl, applied at 70, 140, and 280 g·ha⁻¹ postemergence (POST) would control mugwort (Artemisia vulgaris) in an abandoned nursery. These were compared with the commercial standards picloram at 280 g·ha⁻¹ a.i. and clopyralid at 280 g·ha⁻¹. In the field study, picloram and clopyralid controlled mugwort 75% and 31% by 365 days after treatment (DAT), respectively. In contrast, aminopyralid and aminocyclopyrachlor-methyl applied at 140 g·ha⁻¹ controlled mugwort over 90% by 365 DAT. In the greenhouse study, aminopyralid and aminocyclopyrachlor-methyl applied at 140 g·ha⁻¹ controlled mugwort 92% and 96% respectively, although aminopyralid at 70 g·ha⁻¹ provided better visual control (94%) in comparison with aminocyclopyrachlor-methyl (79%) at 70 g·ha⁻¹. Regardless, following shoot growth removal at 30 DAT, mugwort failed to regrow by 60 DAT following exposures to all rates of both herbicides. On the basis of these studies, aminopyralid and aminocyclopyrachlor-methyl have potential to provide excellent control of mugwort compared with the current standards clopyralid and picloram.

Selective weed control in ornamental plant production can be difficult as many herbicides can cause unacceptable injury. Research was conducted to evaluate the tolerance of several ornamental species to applications of p-hydroxyphenylpyruvate dioxygenase (HPPD)-inhibiting herbicides for the control of problematic weeds in ornamental production. Mestotrione (0.09, 0.18, and 0.36 lb/acre), tembotrione (0.08, 0.16, and 0.32 lb/acre), and topramezone (0.016, 0.032, and 0.064 lb/acre) were applied alone postemergence (POST) in comparison with the photosystem II-inhibiting herbicide, bentazon (0.5 lb/acre). All herbicide treatments, with the exception of the two highest rates of tembotrione, caused less than 8% injury to ‘Noble Upright’ japanese holly (Ilex crenata) and ‘Compactus’ burning bush (Euonymus alatus). Similarly, no herbicide treatment caused greater than 12% injury to ‘Girard’s Rose’ azalea (Azalea). Conversely, all herbicides injured flowering dogwood (Cornus florida) 10% to 23%. Mesotrione- and tembotrione-injured ‘Radrazz’ rose (Rosa) 18% to 55%, compared with only 5% to 18% with topramezone. ‘Siloam June Bug’ daylily (Hemerocallis) injury with topramezone and tembotrione was less than 10%. Topramezone was the only herbicide evaluated that provided at least 93% control of redroot pigweed (Amaranthus retroflexus) with all application rates by 4 weeks after treatment (WAT). Redroot pigweed was controlled 67% to 100% with mesotrione and tembotrione by 4 WAT, but this activity was variable among application rates. Spotted spurge (Chamaesyce maculata) was only adequately controlled by mesotrione applications at 0.18 and 0.36 lb/acre, whereas chamberbitter (Phyllanthus urinaria) was not controlled sufficiently with any herbicide evaluated in these studies. Yellow nutsedge (Cyperus esculentus) was suppressed 72% to 87% with mesotrione applications at 0.18 lb/acre or higher and with bentazon at 0.5 lb/acre by 4 WAT. All other herbicide treatments provided less than 58% control of yellow nutsedge. In the second study, ‘Patriot’ hosta (Hosta), ‘Green Sheen’ pachysandra (Pachysandra terminalis), autumn fern (Dryopteris erythrosora), ‘Little Princess’ spirea (Spiraea japonica), ‘Green Giant’ arborvitae (Thuja plicata), and ‘Rosea’ weigela (Weigela florida) displayed no response to topramezone when applied at 0.024 and 0.095 lb/acre. Since 10 ornamental species in our studies exhibited less than 10% herbicidal response with all rates of at least one HPPD-inhibiting herbicide then it is possible that these herbicides may provide selective POST weed control in ornamental production systems.

Trumpetcreeper (Campsis radicans) is a native, perennial, weedy vine of pastures, row crops, fence rows, and right-of-ways throughout most of the eastern United States. Field and greenhouse studies were conducted in 2008 and 2009 near Newport, TN, and in Knoxville, TN, to evaluate aminocyclopyrachlor-methyl and aminopyralid alone and in mixtures with 2,4-D and diflufenzopyr for selective trumpetcreeper control when applied postemergence in an abandoned nursery. These treatments were compared with commercial standards of dicamba and a prepackaged mixture of triclopyr plus 2,4-D. In the field, aminocyclopyrachlor-methyl alone controlled trumpetcreeper 77% to 93%, while aminopyralid alone only controlled trumpetcreeper 0% to 20% by 12 months after treatment (MAT). The addition of diflufenzopyr or 2,4-D to aminocyclopyrachlor-methyl did not improve trumpetcreeper control in the field; however, the addition of 2,4-D to aminopyralid improved control of trumpetcreeper from 50% to 58%. All aminocyclopyrachlor-methyl treatments controlled trumpetcreeper greater than or equal to dicamba and the prepackaged mixture of triclopyr plus 2,4-D. In the greenhouse, aminocyclopyrachlor and aminocyclopyrachlor-methyl applied at 8.75 to 35 g·ha⁻¹ controlled trumpetcreeper 58% to 72% by 1 MAT. When both herbicides were applied at 70 g·ha⁻¹, aminocyclopyrachlor controlled trumpetcreeper 64%, while aminocyclopyrachlor-methyl controlled trumpetcreeper 99%, similar to dicamba.