per nursery (Gilliam et al., 1990; Evaluation of p-Hydroxyphenylpyruvate Mathers, 1999). Yet, control options Dioxygenase-inhibiting Herbicides for for mugwort are limited due in part to challenges presented by herbicide costs, Controlling Mugwort herbicide phytosafety across desirable crop commodities (including turfgrass 1,2,7 1,3,5 2,6 and ornamentals), and limited efficacy William E. Klingeman , Gregory R. Armel ,HenryP.Wilson , available herbicides may have on other Thomas E. Hines4,6,JoseJ.Vargas1, and Philip C. Flanagan1 key weed species. For example, ethyl N, N-di-n-propylthiolcarbamate applica- tion at 15 lb/acre has controlled mug- ADDITIONAL INDEX WORDS. Artemisia vulgaris, atrazine, bentazon, clopyralid, false wort in field nurseries, yet this rate is chrysanthemum, HPPD, mesotrione, PSII inhibitor, topramezone toohightosafelymanagemugwortin SUMMARY. Mugwort (Artemisia vulgaris) is a perennial invasive weed species that stands of field corn (Bing and Pridham, has infiltrated row crops, turfgrass, ornamentals, and various noncrop areas. 1963, 1964). Glyphosate is effective on Currently, multiple mimics of indole-3-acetic acid can provide control of this young mugwort plants but is less effec- species; however, these herbicides can damage certain sensitive ornamental plants. tive at controlling large mugwort plants When applied at reduced rates, the p-hydroxyphenylpyruvate dioxygenase (HPPD)- in later stages of growth (Ahrens, 1976; inhibiting herbicides mesotrione and topramezone have demonstrated some Bradley and Hagood, 2002a, 2002b). selectivity among certain ornamental plants. Field and greenhouse studies were initiated to evaluate whether these herbicides could control mugwort when applied Plant growth regulating herbicides that alone, or in mixtures with photosystem II (PSII)-inhibiting herbicides that often mimic indole-3-acetic acid, like 2,4- provide synergistic weed control. In the field, mesotrione controlled mugwort dichlorophenoxyacetic acid and clopyr- between 30% and 60% by 21 days after treatment when applied at 0.093 to 0.187 alid, have generally provided poor lb/acre. When the PSII-inhibiting herbicide atrazine was added, control increased mugwort control, even at high applica- to 78% and 79%. In the greenhouse, similar rates produced greater control in tion rates (Ahrens, 1976; Bingham, mugwort, and all mesotrione treatments limited mugwort regrowth by at least 95% 1965; Bradley and Hagood, 2002a, when compared with untreated control. When HPPD inhibitor rates were reduced 2002b; Day et al., 1997). Clopyralid further, the addition of the PSII inhibitors atrazine or bentazon was not sufficient at providing acceptable control of mugwort. can control mugwort and reduce regrowth the following year, yet clo- pyralid is relatively expensive, has lim- ugwort or false chrysanthe- crop plants (Barney and DiTommasso, ited efficacy against other commonly mum is an adaptable, non- 2003; Bradley and Hagood, 2002a, encountered weed species, and is chal- Mnative perennial plant that is 2002b; Holm et al., 1997; Rogerson lenged by limited crop safety across a management challenge to commer- and Bingham, 1964; Uva et al., 1997). a diverse assemblage of ornamental cial agronomic and ornamental crop In nursery fields, rhizomes are abundant plant species (Bradley and Hagood, production worldwide (Barney and in the upper 4 inches of soil (Pridham, 2002a, 2002b; Bradley et al., 2000; DiTommasso, 2003; Henderson and 1963; Rogerson and Bingham, 1964). Day et al., 1997; Koepke-Hill et al., Weller, 1985; Holm et al., 1997; Uva Tillage will exacerbate localized 2011). Still, the broad utility of clopyr- et al., 1997). In the eastern United mugwort infestation because rhi- alid (StingerÒ and TranslineÒ;Dow States, mugwort has expanded be- zome sections 2-cm long reproduce AgroSciences, Indianapolis, IN) across yond ornamental nurseries into turf, well when grown in pine bark, sand, corn, sugarbeet (Beta vulgaris), pasture pastures, and cropping systems includ- and soil substrates (Guncan, 1982; and rangeland, Christmas tree, orna- ing corn (Zea mays), cotton (Gossypium Klingeman et al., 2004; Rogerson mental plant, and fruit and vegetable hirsutum), and soybean (Glycine max) et al., 1972). crop production systems makes this (Bradley and Hagood, 2002a, 2002b; Postemergence (POST) control herbicide a practical choice for selective Yelverton et al., 2012). of weeds in nursery operations re- control of mugwort. Mugwort reproduction and dis- mains a particularly attractive option Mesotrione and topramezone persal is achieved primarily by transport for both field-grown and container impede carotenoid biosynthesis by of rhizome pieces on contaminated cul- production systems due, in part, to inhibiting the enzyme p-HPPD (Norris tivation equipment and within soil and need to reduce labor costs incurred et al., 1998). Mesotrione is registered soilless substrates around the roots of for hand-weeding in addition to the for preemergence (PRE) and POST current practice of making about applications in corn and turfgrass 1Plant Sciences Department, The University of Ten- three annual herbicide applications (BASF, 2013; Mitchell et al., 2001; nessee Institute of Agriculture, Knoxville, TN 37996 2Professor 3Assistant Professor Units 4Research Associate To convert U.S. to SI, To convert SI to U.S., 5Current address: BASF Corporation, Research Tri- multiply by U.S unit SI unit multiply by angle Park, NC 27709. 0.3048 ft m 3.2808 6Current address: Eastern Shore Agricultural Research 9.3540 gal/acre LÁha–1 0.1069 and Extension Center, Virginia Tech, Painter, VA 2.54 inch(es) cm 0.3937 23420. 1.1209 lb/acre kgÁha–1 0.8922 7Corresponding author. E-mail: [email protected]. 6.8948 psi kPa 0.1450 • August 2014 24(4) 433 RESEARCH REPORTS Syngenta Crop Protection, 2011, (Weigela florida), spiraea (Spiraea ja- All treatments contained 1% (v/v) crop 2012) and provides effective POST ponica), arborvitae (Thuja plicata), oil concentrate [COC (Agridex; Hel- control against many annual broad- herbaceous daylily (Hemerocallis), ena Chemical, Memphis, TN)] and leaf weeds and certain grass species hosta (Hosta), autumn fern (Dryopteris 2.5% (v/v) urea ammonium nitrate (Armel et al., 2003, 2009; Beckett erythrosora), and pachysandra (Pachy- (UAN) solution. Experimental plots and Taylor, 2000; Sutton et al., sandra terminalis) (Cutulle et al., were8.3ftwideby20ftlongandwere 1999). Topramezone is also regis- 2013b). arranged in a randomized complete tered for POST weed control in corn Few selective weed control op- block (RCB) design with three repli- and turfgrass (e.g., Amvac, 2007; tions are available for mugwort con- cates. Mugwort control was assessed BASF, 2013). Apparent as foliar pho- trol, and it generally is not adequately visually at 7, 14, and 21 d after treat- tobleaching, topramezone reduces controlled with single applications or ment (DAT) using a 0% to 100% scale, total chlorophyll, b-carotene, lutein, reduced rates of POST herbicides where 0% represented no mugwort and other xanthophyll cycle pig- (Bradley and Hagood 2002a, 2002b). control and 100% represented com- ments in susceptible grassy and It follows that synergistic mixtures of plete mugwort necrosis. Following broadleaf weeds, including common reduced rates of HPPD and PSII in- a land manager decision to mow ex- bermudagrass (Cynodon dactylon), hibitors could optimize weed control perimental field plots in advance of hybrid bermudagrass (C. dactylon · and increase herbicide tolerance to right-of-way remediation efforts, field C. transvaalensis), and annual blue- turfgrass and ornamental crops (Cutulle trials were ended before regrowth data grass (Poa annua) (BASF, 2013; et al., 2013b). Therefore, objectives of could be taken. An alternative site with Brosnan et al., 2011; Elmore et al., this research were to evaluate low rates sufficient contiguous mugwort infesta- 2011, 2013). of the HPPD herbicide mesotrione and tion could not be found to repeat and In limited tests with ornamental to assess control efficacy of mesotrione extend the field trial component. plants, some HPPD herbicides have combined with known synergist like the GREENHOUSE EXPERIMENTS. provided acceptable ornamental tol- PSII inhibitor atrazine for enhanced Greenhouse experiments in Virginia erance at rates that provide some level activity on mugwort compared against were initiated in 2001 to evaluate of weed control (Armel et al., 2009; the standard clopyralid. The second mugwort control using previously Elmore et al., 2013; Little et al., 2004; objective was to quantify the ability field-tested rates of mesotrione (0.093, Senesac and Tsontakis-Bradley, 2007; of reduced rates of multiple HPPD- 0.125, and 0.187 lb/acre), and the Stamps and Chandler, 2009). In- inhibiting herbicides, either alone or lowest mesotrione rate plus a low creased POST control of some peren- paired with the PSII-inhibiting herbi- atrazine rate (0.250 lb/acre), with nial weed species was achieved when cides atrazine or bentazon, to provide efficacy evaluated against the clopyr- HPPD-inhibiting herbicides, like mes- commercially acceptable mugwort con- alid herbicide standard. Five 1-inch- otrione, were combined with other trol for ornamental plant producers, long mugwort rhizomes were planted herbicides, especially those that inhibit whethergrowingincontainerorfield into 4-inch square pots (TO Plastics, PSII inhibitors (Bradley et al., 2000; systems. Virginia Beach, VA) filled with com- Kaastra et al., 2008). For example, mercial potting mix (Pro-Mix BX; POST