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Mesotrione {2-[4-(methylsulfonyl)-2-nitrobensoyl]-1,3-cyclohexanedione} is a herbicide that indirectly inhibits phytoene desaturase in plant tissues, the first step in the carotenoid biosynthesis pathway. The predominant symptom of mesotrione activity is tissue whitening with subsequent plant necrosis. In the current study, ‘Riviera’ bermudagrass [Cynodon dactylon (L.) Pers.] was treated with mesotrione at 0.28 kg·ha⁻¹ or untreated and sampled for tissue pigment concentrations at 0, 3, 7, 14, 21, 28, and 35 days after treatment (DAT). Visual tissue whitening in mesotrione-treated plants reached a maximum of 38% by 14 DAT; however, regreening of discolored tissue was observed by 21 DAT. Phytoene was only detected in mesotrione-treated plants at 3, 7, and 14 DAT. Pigments in treated plants decreased with initial tissue whitening; however, most recovered to untreated levels by 21 DAT. At 35 DAT, chlorophyll a, chlorophyll b, lutein, β-carotene, and zeaxanthin in mesotrione-treated plants had accumulated to levels exceeding untreated control plants. Results demonstrate that although mesotrione initially decreases bermudagrass pigment concentrations, treatment with this herbicide eventually results in higher concentrations of chlorophylls and carotenoids.

Mesotrione, topramezone, and tembotrione are inhibitors of the enzyme p-hydroxyphenylpyruvate dioxygenase (HPPD), which impacts the carotenoid biosynthetic pathway. An experiment was conducted to determine the effects of mesotrione, topramezone, and tembotrione on carotenoid pigment concentrations in common bermudagrass [Cynodon dactylon (L.) Pers.; cv. Riviera] leaf tissues. Bermudagrass plants were treated with three rates of mesotrione (0.28, 0.35, and 0.42 kg·ha⁻¹), topramezone (0.018, 0.025, and 0.038 kg·ha⁻¹), and tembotrione (0.092, 0.184, and 0.276 kg·ha⁻¹). The lowest rate of each herbicide represented the maximum labeled use rate for a single application. Percent visual bleaching was measured at 3, 7, 14, 21, 28, and 35 days after application (DAA). Leaf tissues were sampled on the same dates and assayed for carotenoids. Topramezone and tembotrione bleached bermudagrass leaf tissues to a greater degree than mesotrione. Concomitantly, topramezone and tembotrione also reduced total chlorophyll (chlorophyll a + b), β-carotene, lutein, and total xanthophyll cycle pigment concentrations (zeaxanthin + antheraxanthin + violaxanthin) more than mesotrione. Increases in visual bleaching resulting from application rate were accompanied by linear reductions in lutein, β-carotene, and violaxanthin for all herbicides. Topramezone and tembotrione increased the percentage of zeaxanthin + antheraxanthin in the total xanthophyll pigment pool (ZA/ZAV) 7 days after peak visual bleaching was observed at 14 DAA. Reductions in ZA/ZAV were reported after 21 DAA. This response indicates that sequential applications of topramezone and tembotrione should be applied on 14- to 21-day intervals, because stress induced by these herbicides is greatest at these timings. Increases in photoprotective xanthophyll cycle pigments (ZA/ZAV) at 14 to 21 DAA may be a mechanism allowing bermudagrass to recover from HPPD-inhibiting herbicide injury, because bermudagrass recovered from all treatments by 35 DAA. Data in the current study will allow turf managers to design physiologically validated bermudagrass control programs with HPPD-inhibiting herbicides. Chemical names: mesotrione [2-(4-methysulfonyl-2-nitrobenzoyl)-1,3-cyclohexanedione], tembotrione {2-[2-chloro-4-(methylsulfonyl)-3-[(2,2,2-(trifluoroethoxy)methyl]benzoyl]-1,3-cyclohexanedione}, topramezone {[3-(4,5-dihydro-3-isoxazolyl)-2-methyl-4-(methylsulfonyl)phenyl](5-hydroxy-1-nethyl-1H-pyrazol-4-yl)methanone}.

Members of the Allium genus are consumed for their culinary flavor attributes, but also contain antioxidant and anticarcinogenic phytochemicals. Bunching onions (Allium fistulosum L.) are commonly used in Asian cuisine, in which both leaves and pseudostems are consumed. Carotenoids and chlorophylls are important classes of phytochemicals gaining attention for their health attributes. The goal of our study was to characterize carotenoids and chlorophylls and identify possible genetic and environmental influences on carotenoid concentrations among A. fistulosum accessions. Twelve USDA-ARS accessions were field grown in Knoxville, TN, and Geneva, NY, during the summer of 2007. After harvest, carotenoid and chlorophyll pigments were evaluated in leaf and pseudostem tissues using high-performance liquid chromatography. We were able to identify the presence of antheraxanthin, β-carotene, chlorophyll a and b, lutein, neoxanthin, and violaxanthin in leaf tissues; however, pigments were not found in pseudostem tissues. Carotenoid and chlorophyll concentrations did not differ among accessions or between locations. It is possible that accessions evaluated in this study were a narrow genetic base or were selected based on flavor attributes and not leaf tissue pigmentation.

Ornamental plant growers must be able to accurately assess production costs associated with woody liner stock to gain profit potential in a highly competitive industry. Fixed and variable cost inputs may not be intuitive or readily apparent to growers and may even differ between common types of production in the trade. To help liner producers identify profit-based price points for their woody ornamental liner stock, we modeled costs associated with producing familiar species and cultivars of a representative deciduous shade tree, a broadleaf evergreen, and a needle leaf evergreen liner. Production costs are projected down to individual plant units for each of the three most common liner production systems, including a field ground bed system, a polyhouse-covered (plant protection structure sheathed with one layer of 6-mil polyethylene film) ground bed system, and a polyhouse-covered container system. Production costs for individual plants varied due to the actual growing space available within each system. The field ground bed system offered greatest flexibility in crop planting density, with cost potentially distributed among the largest number of salable units. In addition to modeled costs, advantages and disadvantages of each liner cropping system are discussed.

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.